sellecting cylinder heads

Discussion in 'Cams, Heads and Valve Trains' started by grumpyvette, Nov 26, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member


    read these threads and sub-links also, as they contain good info, if you fail to read thru the sub links youll miss a ton of useful info, don,t think published flow numbers or price alone are the only really useful factors to use, remember a flow bench has very little in common with a running engine
    keep in mind that a properly designed exhaust system and headers goes a very long way towards increasing the efficiency of the intake manifold and head flow , and remember that the better the heads and the more effective the exhaust scavenging the less duration the cam used will require!


    before as cast
    after port clean up intake
    before as cast
    after port clean up exhaust
    most stock and some aftermarket heads benefit from port and bowl clean up work,to smooth and increase flow rates ,port throats generally run 80%-85% of total valve diameter because you need to maintain sufficient valve seat contact area to allow sealing and cooling and some wear during operation.
    But be aware that using stock refurbished heads , can cost a good deal more than new heads will,because its very likely that by the time you hot tank or oven and shot-blast clean them
    , have them dye or magnetically checked for cracks and pressure and have, a clean-up decking,pass on the milling machine,insert new valve guide inserts, select and install bigger valves , and that requires new valve seats with a good multi angle valve job, pay for and install the correct matched springs, keepers, and retainers,that came with the new cam, if you bought the matching components instead of trying to keep cost low and use the O.E.M. valve springs which are unlikely to match the application, you might be better off to buy new cylinder heads??


    a very common misconception, "that the intake runner size has the most effect on the engines torque curve,is mostly a myth" in reality ,compression ratio, cam timing and engine displacement and proper exhaust scavenging ALL have a larger effect on the engines torque that the intake runner cross sectional area.(yes getting it correct helps but your more likely to cause a problem by selecting an intake port and runner combo thats too small and restrictive than one thats too large in cross sectional area.
    heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common


    Some of the More Popular Gen I Cast Iron GM Cylinder Heads

    #3767754 – Manufactured from 1959-1961 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

    #3774692 – Manufactured from 1958-1964 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

    #3795896 – Manufactured from 1963-1965 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

    #3782461 – Manufactured from 1964-1966 on 327 Cubic Inch engines. 161/62 cc port volumes, 62cc combustion chamber. Identified by Double Camel hump symbol.

    #3782461X – Manufactured from 1960-1963 on 283 and 327 Cubic Inch engines. 172/64 cc port volumes, 62cc combustion chamber. Identified by Double Camel hump symbol.

    #3890462 – Manufactured from 1966-1967 on 302, 327, and 350 Cubic Inch engines. 64cc combustion chamber. Identified by Camel hump symbol. No accessory mounting holes.

    #3917291 – Manufactured from 1967-1968 on 302, 327, and 350 Cubic Inch engines. 64cc combustion chamber. Identified by Camel hump symbol.

    #3932441 – Manufactured from 1969-1970 on 350 Cubic Inch engines. 161-165cc intake port. 76cc combustion chamber.

    #3932441X – Manufactured from 1969-1970 on 350 and 400 Cubic Inch engines. 161/65cc ports. 80cc combustion chamber. 1.94″ intake/1.5″ exhaust valves.

    #333881 – Manufactured from 1974-1975 on 350 Cubic Inch engines. 76cc combustion chamber. 2.02″ intake/1.6″ Exhaust valves.

    #3991492 – Manufactured from 1970 on 350 Cubic Inch engines. Available on the LT1 engine and over the counter. 64cc combustion chamber. Either straight or angled plugs.

    Intake Port cc & CFM @. 500" Lift

    Chevrolet Production 441 Iron Head 155/201

    [​IMG]The 882 head may have out-flowed this head but with the addition of larger 2.02-inch intake valves and some decent pocket port work these heads will out flow the 882’s. Keep in mind that with a small 155cc port volume these heads are great for making torque.


    Chevrolet Production Iron 882 Head 151/205

    [​IMG]This head had the smallest port size of all the heads we tested. A set of 2.02/1.60-inch valves can be swapped in but be aware that without blending in the short side radius, the results usually find lost airflow.

    Chevrolet Production 462 Iron Head 156/212

    This head was a small chamber head used on 327ci motors until the end of 1968. The flow can be improved a little with larger valves and port work but the additional cost of this is impractical in comparison to what you can by some other aftermarket casting for.

    Chevrolet Production Vortec Iron Head 885 170/239

    This head can be seen as a sleeper when compared to other GM production heads. It outflows the LT-1 aluminum Corvette head on the intake side, plus its mid lift numbers are very impressive. This head is perfect when iron heads are required. GM designed this head and put it on trucks as well as on the later Impala SS but with a different intake bolt pattern. As for production pieces these are one of our favorites.

    Chevrolet Production L98 TPI Aluminum Head 163/196

    [​IMG]This aluminum head was used on the Corvette TPI engines from the mid-Eighties until the LT-1 1992 motors were introduced. The 882-iron head out-flowed this head across the board. This piece is not our first choice for a performance head considering that the largest valve this head fits is a 2.00/1.55-inch combination and it has a 58cc chamber.


    Chevrolet Production GM LT1 372 Aluminum Head 170/214

    [​IMG]The LT-1 head was the next generation head developed for the small blocks after the L98 head. This head uses a reverse-cooling system, which means it can not be swapped onto older blocks. The 0.400-inch airflow numbers are great and with some port work, the addition of 2.00/1.55-inch valves can really wake these heads up.

    Chevrolet Production LT4 Aluminum Head

    [​IMG]The LT-4 is substantially different from the LT-1 casting, and the flow numbers explain why. The larger intake ports are definitely a contributing factor. For a production head these babies put up some pretty good flow numbers. Remember, like the LT-1 the LT-4 can only be used on a reverse cooling system block.
    Chevrolet LS1 Aluminum Head 204/240

    [​IMG]GM won’t be left out of category 3 with these heads. This head has great 0.400-inch lift numbers as well as a good E/I ratio. They also feature a more flat valve angle (15 degrees) in order to promote a better combustion chamber that’s shaped like a kidney to help direct combustion and reduce possible detonation. Remember that this head will not interchange with pre-‘93 small-block heads.


    AirFlow Research 180 Aluminum Head 181/250
    [​IMG]This head is the smallest of AFR’s line. It is intended for engines up to 350ci. The flow numbers are especially impressive on the exhaust side of this head, leading us to believe that a single pattern cam may be the best choice here. The E/I relationship is outstanding with and 84%, almost higher than any other head in this category.

    AirFlow Research 190 Aluminum Head 191/262

    [​IMG]This head has the best flow numbers of all the category 2 heads. Offering great flow throughout the entire lift range you can see this head doesn’t just put up one big number at maximum lift. If you’re looking for great flow from a mid-sized cylinder head this is definitely one of the top contenders.


    AirFlow Research 210 Aluminum Head 215/271
    Here is an extraordinary head. It has larger intake ports but with 240cfm at 0.400-inches of lift who cares? The E/I ratio is an incredible 75% making it hard to find anything wrong with these heads. This head may be a little much for a mouse motor but it is perfect for a big mouse somewhere in the 383 inch range up.
    Brodix-8 Pro Aluminum 181/254

    [​IMG]This head features larger 2.08/1.60-inch valves combined with a 181cc-intake port. With smaller intake port this head flows outstanding at 220cfm by 0.400-inches of lift and even better by 0.500-inches. Combined with a mid-sized port this, this is an outstanding choice for a strong 350ci or 383ci motor.


    Brodix Track 1 Aluminum Head 216/246

    The Track 1 head may be down on the numbers at 0.400-inch lift but it’s really competitive once it sees the 0.500-inch lift point. Add some short-side radius work and wow you’ve got a killer head. If you have a set of these heads there’s definite potential.


    Brodix -11X 220 Aluminum Head 216/246

    [​IMG]Brodix offers this large-port, 23-degree valve angle, small-block head as one of its largest ports in the stock valve-angle lineup. The low lift numbers are down a bit but in comparison to some of the others once the lift numbers increase you can see there is some serious airflow. These come available with minor or major port work depending on how you order them.


    Brodix -1X Aluminum Head 223/278

    [​IMG]The Brodix -1x heads feature a 40/60 valve spacing, meaning the centerline of each valve has been moved away from its standard location to accommodate a larger diameter valve and move both valves away from chamber walls for unshrouding. This means special offset shaft mounted rockers are needed and available from Brodix. It seems like a lot of R & D went into these bad boys and the numbers show it.


    Canfield Aluminum Head 195/258

    [​IMG]Canfield only sells this head with valves. One area to pay close attention to is the excellent low and mid-lift numbers. This head actually out-flows the Category 3 heads from 0.050- through 0.400-inches of lift.


    Canfield 220 Aluminum Head 223/260

    [​IMG]This race oriented small-block head requires the use of 0.150-inch offset intake rocker arm to accommodate the repositioned intake valve. The idea of spreading the valves apart is to increase valve diameter and improve flow. This head has 2.08/1.60-inch valves and probably works best on larger displacement mouse motors around 383-plus cubic inches.


    Dart Iron Eagle S/S 165/210

    [​IMG]Dart offers everything from street performance heads to full race heads. This Iron Eagle piece is the smallest head at 165cc port volume but its just what you need when building a stout street motor that sees occasional strip time. Compare its flow numbers to others and you can be the judge on this one.

    Dart Iron Eagle 180 174/210

    [​IMG]This head is also a big brother but to the 165cc Dart Iron Eagle head. The 180cc head reveals a respectable intake flow curve and an outstanding exhaust port. This head comes in many different combinations. You can order the head with straight or angle plugs, a 64cc or 72cc chamber, and in iron or aluminum. You will notice this head has better mid lift intake flow figures but the same full lift numbers as the 165cc heads, however the exhaust side flows better.


    Dart Iron Eagle 220 220/258

    [​IMG] The Dart Iron Eagle head here offers a budget alternative to the aluminum Conquest head. With similar flow numbers the only real big difference here is iron verse aluminum and cost. This head is offered in 200 or 220cc intake ports and with 2.02 or 2.05-inch intake valves.


    Dart Conquest Iron 220 220/252

    [​IMG]This head really likes to flow at lifts above 0.500-inches. The E/I ratio at 0.400-inch is a very good 72% and 68% at 0.500-inches. This head comes machined for both center-bolt and perimeter-style valve covers. The Conquest can be optioned with 200 or 220cc intake ports, valves up to 2.08/1.60, and in 64 or 72cc chamber sizes.

    Dart Pro 1 Aluminum 215 221/253

    [​IMG]This is perhaps one of the most versatile heads out there. While the low lift numbers don’t stand out, the higher lift numbers are on par with the rest of the heads on the market. This head is definitely best on high winding motors where consistent rpm is what wins a race.


    Dart Iron Eagle 230 229/254

    [​IMG]This is the largest of the Dart Iron Eagle series heads. They perform best on motors above 400ci-inches and with cam lifts above 0.500-inches lift. The E/I ratio is acceptable and the castings are made of good quality. These heads flow well and do not really require too much handwork to improve airflow.

    Edelbrock Performer Aluminum 166/235

    [​IMG]This head may first appear subtle in comparison to its flow numbers but don’t be fooled. The 166cc port makes for great torque and the E/I flow relationship is good. This head is perfect for a street/strip application. In our own personal experience we had a 355ci motor with 9:1 compression, a streetable Comp Cam (DEH 275), and an Edelbrock RPM manifold. With this combination we were able to achieve 420hp at 6,000rpm and 440 lb-ft of torque at 4,250 rpm.

    Edelbrock Performer RPM Aluminum 170/237

    [​IMG]The Edelbrock RPM head is the big brother to the Performer version. It still retains a small 170cc intake port volume providing great torque down low where it’s needed. The E/I percentage is no less than 70% with much higher numbers in the low-lift areas. This head is a step up from the Performer, flowing more air, which in return will make more power on the top end.

    Edelbrock E-TEC 170 Vortec Aluminum 170/240
    [​IMG]With the tremendous popularity of GM’s Vortec head, Edelbrock decided to design a head around the GM casting. This head features a 1.94/1.55-inch valve combination, and different port configuration allowing it to out perform the stock production Vortec head. However, the E-TEC heads are aluminum typically costing more than the production GM heads.

    Edelbrock E-TEC Vortec 200/252

    This head is the next step up from the smaller 170 E-TEC. It features larger valves and bigger intake ports. However, a Vortec style intake manifold must be matched with these heads. Up to 0.500-inches these heads don’t really out flow the stock Vortecs. On the other hand their exhaust ports are extremely efficient which help improve performance throughout the entire power curve. They are also aluminum, which can allow more compression with out detonation.


    Edelbrock Victor Jr. Aluminum 219/255

    [​IMG]This is an impressive head. It features a kidney shaped combustion chamber keeping the combustion moving, the flow is awesome from 0.400-inches all the way up to our tested 0.700-inches, and the E/I ratio is an amazing 81%. We see a head that flows some serious air and likes high lift roller cams.


    Holley 300-570 Aluminum 172/232

    [​IMG]This head from Holley comes with angled plugs and 69cc chambers, which are a big change from the stock 76cc smog chambers. The combustion chamber is typical of a late model design with a kidney shape that increases combustion turbulence lessening the possibility of detonation.


    Holley SysteMAX Aluminum 186/242

    [​IMG]This head is very similar to the -8 Brodix but it appears to flow a little better on the exhaust side. Again this head looks like it offers great torque potential with its well-proportioned 186cc-intake runner


    Pro Action Iron 220 225/239

    [​IMG]These heads can be purchased in many different intake port sizes. They are available with 180, 200, 220, and 235cc intake ports. They also feature a 64cc and 72cc chamber for your desired compression levels.


    Pro Action Iron 235 Iron 245/242

    [​IMG]These are the largest of the Pro Action lineup. The heads are advertised as 235cc intake ports but in our testing we found them to be 245cc’s. These heads are definitely for use on big mouse motors that like to see some rpm.


    Trick Flow Specialties 195 195/250
    These heads may not flow the biggest numbers but there should be little question regarding their performance that they can perform well. In CHP’s Nov. ’99 issue they were bolted on a mild 383ci motor and were able to pump up peak engine power by 15.5%. These heads offer some of the best power for the dollar on a mild small Chevy.


    TFS Twisted Wedge 200/254

    [​IMG]In an attempt to be different for the better, this TSF twisted Wedge head changed the valve angles from 23 degrees to 13 degrees. The really big difference here is what the exhaust side of this head is capable of. Only one other head (AFR 210) was even close on the exhaust side. The E/I was also a very respectable 77%. This head really can wake up your engine.


    World Products Iron S/R Torquer 170/225

    [​IMG]This head is very similar to the 882 head tested earlier. The valves are larger and the flow numbers at 0.400-inch lift are almost identical. At 0.500-inch lift the flow is up 15% over the 882 head. With prices to rebuild stock heads increasing all the time these heads would probably be one of your better investments.

    CHEVY 882 smogger heads

    rhs heads

    you might want to watch this 4 part video

    one issue I see is the constant mental disconnect between the guys intended use when someone buys cylinder heads based on the posted flow numbers, and reality,
    posted flow numbers and performance that results will vary significantly when you mis-match components especially when guys fail to realize the engine they are building has very few of the same components or dimensions matching the posted
    “I see this problem constantly. If you read in the advertising that a certain cylinder head flows 300 cfm, on a SBC engine , very few people ask at what valve lift and what bore size and then, ask themselves if the engine they build will have much or anything in common. , if they used a 4.155 bore size to test the heads and your bore is less, like a 4.060 the resulting valve shrouding it can kill 30-50 hp because it leaves a ridge all the way around, the combustion chamber that was not there during the advertised flow test. People buy heads that were designed and tested on larger bore sizes or advertised in dyno test articles when an engine used a cam with much higher compression and a much more radical cam with a tighter LSA and more duration, and are stunned and disappointed to find they don,t get similar results using much less duration, lift and compression on a smaller displacement engine! The problem occurs because that valve size and cam lift and duration,must match the intended application, and that port is designed to flow X-amount in order to get the air speed in a certain range. So if your particular engines component list is nowhere close to the magazine articles configuration, you’ve not only killed the potential airflow, but you’ve killed the air speed and completely destroyed the advertised flow dynamics of the cylinder head you based the cylinder heads purchase on ,expecting the heads to flow as advertised.”
    this works at both extremes, I see guys buy cylinder heads with much to small/restrictive ports who are convinced that a larger head will kill all the low rpm torque, only to find the heads strangle the upper rpm power,and guys that over cam an engine with too low of displacement and compression, and who fail to install effective headers and a low restriction exhaust behind the headers, who then erroneously blame the cylinder head port size for the lack of power that results.
    you should read the links they contain a wealth of info

    USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations[/color] ... -23-degree


    viewtopic.php?f=52&t=10602&p=45479#p45479 ... _Big_Block






    A VIDEO DART VS 882 chevy heads TO WATCH ... v3ZkqZiMjI


    measuring throat cross sectional area



    viewtopic.php?f=52&t=410&p=1907#p1907 ... 5/A-P1.htm ... /A6-P1.htm

    as you can see in this chart, below most of the stock heads don,t flow as well as the AFR 195cc heads and there ARE better flowing heads, but keep in mind the stock heads were never designed as race components, in most cases the engineers were more concerned with cost and low and mid range speed & torque.
    A cylinder head that might be perfectly adequate for the current application may be woefully restrictive if used on a similar engine if you should choose to swap cams or swap to a well designed exhaust header, change intakes or drive train gearing, so its usually best to hedge your bet a bit on the cylinder heads selected and purchase a cylinder head that has at least some potential to flow at higher valve lifts and higher engine rpm limitations than the current combo may have.
    yes we all deal with budget limitations, so you generally can,t just look for the cylinder heads with the very best flow numbers, and in most cases that would be a far from cost effective route to take. but I would suggest shopping around very carefully before spending your cash.
    a good deal more info posted below so its worth the time to keep reading

    USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations[/color]

    I thought I post these flow numbers on ported vortec heads ive seen posted , just in case anyone has ever wondered or wanted to know the flow numbers a set of stock vortecs. I was also curious if any of you have any guesses on what gains I picked up on the port work.
    .1---------- 59--------- 64--------- +5
    .2---------- 117------- 132------- +15
    .3---------- 170------- 187------- +17
    .4---------- 214------- 236------- +22
    .5---------- 226------- 255------- +29
    .6---------- 219------- 259------- +40
    .1---------- 42----------46--------- +4
    .2---------- 83----------90--------- +7
    .3---------- 123--------139--------+16
    .4---------- 136--------161--------+25
    .5---------- 143--------174--------+31
    .6-----------147------- 178--------+31
    [​IMG] ... index.html ... tions.aspx ... e_2009.pdf


    bbc oval ports making 697hp ... /dyno.html

    heres some guides but keep in mind its NOT the port volume or PORT CCs of total port volume your concerned with, its the port cross sectional area, at its narrow point, you cam timing, compression and displacement, combined with the cars gearing, intake design and exhaust scavenging combined that makes the port size you select work
    it does absolutely no good to place a cylinder head with with a port cross sectional area thats larger than the intake port that feeds it, in a combo as all the abrupt increase in port cross section does is cause increased turbulence, and a sudden loss of port air flow speed and that tends to cause fuel to drop out of the airflow or at least disrupt is even distribution
    in an ideal world ports reduce cross sectional area bye about 3%-5% from entrance to the valve pocket, and the port cross section in the heads a bit smaller than the intake runner.
    cams need to be selected with the engines intended rpm range and power band and the displacement of the engine, plus the engines compression ratio and drive train gearing taken into account, any increase in port cross sectional area above whats required to fill the cylinders in the intended power band tends to reduce efficiency.

    AS your displacement per cylinder increases the effective valve size per cubic inch decreases so you need a slightly tighter LSA and these charts should help.



    so any time you want to stop guessing at the answers, or taking your Buddy,s best guess as a fact, you can use known values & calculations to arrive at valid answers and actually match components



    viewtopic.php?f=69&t=1040&hilit=206cc ... hp?t=17250 ... index.html ... lumes.html

    one factor that gets discussed a great deal is the difference in port size or port CCs, the sad truth is that Id bet 90% of the discussions are just guys repeating stuff they have heard with zero real idea what they are talking about.
    while theres generally some relation of port cross sectional area to the listed port CCs its NOT a direct linear relationship, and its the cross sectional area,shape, length and surface finish not the port CCs that matter to the air flow., and if the exhaust system can,t effectively scavenge the cylinders or the intake can,t supply the flow, or the cam duration and lift don,t match the intended port flow rates performance will suffer

    While theres no direct linear relationship between port flow and hp there is a strong relationship.So you'll generally want the highest flow numbers you can get in any port size ranges as a starting point, and yes theres other factors that go into making hp, so combustion chamber design,compression, cam timing, cylinder scavenging ETC. will effect might want to keep in mind that carbs are flow rated at 1.5 inches of mercury, heads at 28" of water and that anyone who has ever watched a vacuum gauge, will tell you the readings fluctuate rapidly, under most conditions and vacuum tends to vary with the cam,used the rpms the engines running, displacement and intake design,exhaust scavenging,ETC.
    in most cases there factors are at least, mostly or on occasion, partly understood well enough that theres formulas and charts that can be used to define probable results, that parts selection will result in to a reasonable degree.

    you don,t build an engine combo by selecting just heads, first and then matching the other components to that head flow rates, you select a hp/torque/rpm power band as a goal and then select the necessary components to slightly exceed that hp/torque/rpm power bands requirements knowing all parts NEVER work at 100% of the potential when matched in a combo.
    the ballpark formula is
    .257 x port flow x 8 = potential hp

    watch the video, and like I stated many times,
    its the combo of the engines,
    displacement ,
    cam timing
    and the exhaust scavenging ,
    and the intake manifold design,
    NOT the intake port cross sectional area,
    that are the most critical factors, in the engines lower rpm and mid rpm torque.
    but for damn sure an intake runner port can be small enough to noticeably restrict upper mid range and peak power significantly,
    For 5 decades I've heard endlessly about how installing larger free flowing cylinder heads would devastate the engines ability to make any low or mid rpm torque.
    especially when Id suggest using a set of smaller 300cc-320cc, aluminum,rectangle port heads on a 496 BBC, or 200 cc-210cc heads on a 406 sbc, I was asked to build
    yet on every engine I've ever had built or had some guy ask me to look at, to see why it ran a great deal less impressively than he expected it too,
    they brought into my shop its was very obvious (at least to me) that it was the combo of low compression, too little displacement, with too much cam duration ,
    a restrictive exhaust or some guy who was trying to save money and continuing to use a stock stall speed torque converter, or retain a badly mis-matched 2.87:1-3.08:1 rear gear ratio,
    with an engine that he miss matched components by slapping a large carburetor , and a single plane intake on,an engine that will rarely exceed 6000 rpm, that was the major reason.
    if you want an engine combo to run your first step is to logically match the list of components you,ll use to the application,
    and that requires you stop, engage the brain and think things through carefully,
    and the most common way to screw up the process is to over cam a low compression engine,
    have a restrictive exhaust or mis-match the drive train gearing to the engines power band.

    if your intake port flows 250cfm
    .257 x 250 x 8 = yields APPROXIMATELY a 514hp figure before your heads become the limiting factor

    this ballpark formula is based on average results FROM WELL TUNED HOT ROD TYPE Engine's USING DYNO FLYWHEEL RESULTS
    NOT true race only engines or street engines
    also keep in mind that the results you'll get will differ and to get those numbers it requires the engine to operate in its best rpm range with a cam and compression levels that match and all other components must also match
    if your heads flow 279 cfm at .700 lift but your intake only flows 240cfm and your cam has a max lift of .550 your not going to get the max potential HP results
    for the ball park formula to work you must have a tuned exhaust, a cam that matches the compression ratio and all other parts must flow at least close to as well as the heads at the max figures
    also keep in mind that the ports cross sectional area should keep the airflow in those ports in approximately the 200fps-300fps ranges
    airflow speeds that very greatly from that 200fps-300fps will not tend to give best results, thats why huge ports that flow exceptionally well don,t work well on smaller displacement engines
    port lenth also has a large effect on the rpm range that the ports can effectively pack the cylinders at due to harmonics in the column of air
    PORT SIZE FLOW AND THE RELATION TO CAM DURATION, and your displacement and the tuned rpm that your headers operate best in for scavageing the cylinders also comes into play here!

    FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand and I’m sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are using
    My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand
    But lets look a a few concepts

    (1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque it’s a race between more power stokes and lower power per stroke

    As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, that’s between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port that’s substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you can’t substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so that’s where are cam and port size must match, you can do the math , (47.875 x ½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

    Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
    Or this helpful info in this thread

    very important calculator info



    Either way you’ll find that you’ll want a port size in the 2.4sq –2.9 sq inch area
    Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6” in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm

    Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
    well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds there’s not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just don’t have the time necessary to flow
    enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now that’s only about 35% of the time and there’s 41.6 intake strokes per second , that’s only 1/60th of a second for air to flow into the cylinder
    Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.
    Volumetric Efficiency
    The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
    this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level
    if you’ve been following along you’ll find that you’ll need intake ports about 2.3-2.9” sq inches in cross section, and between 12” and 21 “ long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!
    Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, that’s why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range

    you might want to watch this video

    the basic rule is a dual plane intake will almost always be the better choice over a single plane intake if the cam duration is under about 235 degrees@.050 lift

    Ive built 383,396,421 and 427 SBC combos and used both the 195cc and 210cc AFR, brodix 180,200cc , trickflow, 195, 215 and dart 200cc,-230cc heads,and Ive used the 750cfm and 850cfm carbs.

    ok theres very little gained with swap between the 750/850 cfm carbs in either direction, both are almost interchangeable with the correct tuning in my opinion, but ID prefer the 750cfm about 90% of the time, as its slightly crisper in the throttle response and Id doubt youll give up 3 hp at peak with the small rated carb

    the 195cc class heads produce slightly more low rpm torque, the 210-230cc slightly more peak hp,in a combo thats set up correctly to take full advantage of either heads characteristics, again the difference is more in the intake, cam, compression and exhaust tuning, but given a choice id select the 210cc heads about 75% of the time if the peak hp was the goal and the 195cc on a car used mostly on the street, as a general rule if I use a single plane intake, and a cam with about 240 plus duration,and 10.2:1 or higher compression, I tend to select the 210-230cc heads, on a dual plane intake , with a cam having under 240 duration,and 10.1:1 or lower compression, Id select the 195-200cc class heads
    keep in mind its that total combo with the rear gearing, exhaust and transmission gearing, car weight, tire diam. fuel octane etc. taken into the calculations that matters not a single component

    Last edited by a moderator: Mar 10, 2018
  2. grumpyvette

    grumpyvette Administrator Staff Member

    I run into so many guys that think you can just un-package new cylinder heads and slap them on any engine they build , and expect those heads to function flawlessly.
    there is almost always at least an extra 15-hp-20-hp or more potentially easily accessed through minor port clean-up.
    if your willing to disassemble the heads, port match the runners and clear up the casting flaws and smooth and contour the bowl area under the valves you could rather easily double or in some cases triple those potential power gains just by improving the port contours and removing casting flaws ... 1/A-P1.htm ... view&id=28 ... index.html

    viewtopic.php?f=52&t=2203 ... lator3.htm ... _database/ ... l#GM%20LT4 ... =76&page=1 ... to_11.html

    theres a good deal of info on assembling a 383 -406 sbc in this thread you might need

    viewtopic.php?f=69&t=261&st=0&sk=t&sd=a&start=10 ... lumes.html ... areas.html

    above is a very typical machine shop invoice for reconditioning a set of used vortec heads, notice theres $982 plus in charges and theres a great deal more that could easily be required to recondition used heads, now add the rather typical purchase price of at least $200-$400 for a set of clean used vortec heads and you quickly find you could buy better heads for the cost involved
    so be aware that just the cost of used or bare heads is not the total cost youll see.

    RELATED INFO, theres a great deal here you should read


    up to the rpm range where the port cross sectional area becomes a restriction to flow a smaller port is usually superior
    for torque produced, larger ports tend to be less responsive and produce slightly lower torque so you need to match the flow to the displacement and rpm range
    Last edited by a moderator: Sep 14, 2018
  3. grumpyvette

    grumpyvette Administrator Staff Member

    read this, BUT keep in mind it does little good to have killer head flow numbers if the intake manifold flows less or if the exhaust is restricting flow, and heads that flow killer numbers at .700 lift, and are designed to feed a 427 displacement at 7500rpm, DON,T do you much good if the CAM you selected has a .520 lift AND ONLY SPIN THE ENGINE TO 6000RPM

    ITS A COMMON MISCONCEPTION,THAT YOU MEASURE PORT CROSS SECTION AT THE PORT ENTRANCE, BUT ITS NOT the port area at the entrance , you need to use in the calculations, ITS the MINIMAL port cross section at the SMALLEST point in the port, usually near the push rod area.
    LIKE a funnel, its not the largest part of the opening but the smallest that's the restriction to flow

    SO HOW do you MEASURE THEN?? ... umber=5649

    [​IMG] ... toview=sku



    heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes


    Potential HP based on Airflow (Hot Rod, Jun '99, p74):
    Airflow at 28" of water x 0.257 x number of cylinders = potential HP
    or required airflow based on HP:
    HP / 0.257 / cylinders = required airflow

    a good deal of the results you see on the EXHAUST side AND THE INTAKE SIDE are greatly effected by the scavenging design rpm range of the headers and the restriction to flow beyond the collectors.
    YOU CAN,T CRAM MORE IN TILL THE OLD F/A CHARGE VOLUME IS REMOVED, and with a properly designed low restriction exhaust , the fast moving exhaust mass in the headers helps to drag in the next intake charge into the cylinders.
    generally you can get a bit of useful info with a pressure gauge, if the exhaust have greater than about 1 PSI you've generally got a restriction that's hurting the power,and that restriction to flow DOES effect the engine tuning results and the cam timing you'll want to use.
    now Ive generally found that the collector lengths on commercial headers are too short and in many cases designed wrong to maximize the cylinder scavenging.
    it does little good to stick a decent set of headers on a car and then hook the collectors up to a restrictive 2" or 2.5" exhaust either.
    if your car runs noticeably better with open headers at the track, you can bet your street exhaust is restrictive.

    there ARE aftermarket header merge collectors and things you can do to reduce the restriction to flow, (THE (H) and (X) pipes that split or share the exhaust between both sides, and a custom 3" exhaust and low restriction mufflers comes instantly too mind here)

    ID suggest you select from heads from these sources
    Jegs; 800/345-4545;

    Summit Racing; 800/230-3030;

    Scoggin-Dickey Parts Center; 800/456-0211;

    TRICKFLOW ... 4294867081
    1-330-630-1555 • 1-888-841-6556


    Dart Machinery; 248/362-1188;

    toll free: 877-892-8844
    tel: 661-257-8124

    Patriot Performance
    Patriot Performance; 888/462-8276;

    Toll Free: 877-776-4323
    Local: 901-259-1134

    EDELBROCK ... main.shtml
    Edelbrock; 310/781-2222;

    BMP (world products)
    Tel: 631-737-0372
    Fax: 631-737-0467




    “Quality means doing it right when no one is looking.”

    Henry Ford

    “Quality is like buying oats. If you want nice, clean, fresh oats, you must pay a fair price. However, if you can be satisfied with oats that have already been through the horse ... that comes a little cheaper.”

    an hour to a week spent in careful research,
    before you buy or install parts,
    can save you months or frustration
    and easily 300%-to 500% of the eventually,
    cost incurred in buying cheaper parts,in this hobby!

    good quality parts tend to cost more, so expect to pay a fair price, remember the sweetness of low price tends to be forgotten long before the bitterness of living with low quality, that remains forever!

    “It is quality rather than quantity that matters.

    “There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply. The person who buys on price alone is this man's lawful prey.”
    John Ruskin

    "the quality of a man's life is in direct proportion to his commitment to excellence, regardless of his chosen field of endeavor".

    IN almost 100% of engine builds, your FAR better off purchasing and correctly installing a few high quality components, than you would be, after spending twice too three times as much money on, three to four times as many low quality parts randomly selected mostly because they were on sale!

    GREAT DEALS!...RARELY ARE, looking back later!
    Last edited by a moderator: Sep 14, 2018
  4. grumpyvette

    grumpyvette Administrator Staff Member

    keep in mind swapping heads gives you the option to increase or decrease the compression ratio of the combo, and once the compression ratios increased you can use a longer duration cam timing without sacraficeing a great deal of low rpm torque, that you would loose with the lower compression ratio if the same cam were installed in the lower cpr combo

    "(assume on a stock 350 small block)

    Speaking in generalities and assuming no other changes, what's the relation between cylinder head combustion chamber size and overall engine compression?

    Does just changing heads from a stock 76cc head, to a head with a smaller chamber make that much overall difference on engine c/ratio? Such as a 64cc or 58cc chamber. How about changes on necessary octane requirement?

    Just curious to see what can be expected. I've read plenty on what performance gains can be had and what would work best for 350 TPI, but curious to see the other factors may play out.


    Ok lets look at it a bit, theres two types of compression ratio, static and dynamic, keep in mind its MOSTLY dynamic compression ratio, that effects your results.
    youll gain about 3% in hp increasing the effective static compression ratio one full point, so swapping from a 9:1 to a 10:1 cpr boost torque about 3%
    swapping from a 76cc head to a 58cc head is a 1.84:1 cpr change so you can reasonably expect a 1.84 x 3% or a 5.52% boost in torque from that change alone.
    if your current engine made 330hp that would jump to about 5.52% higher if the tq curve remained consistant, so youll see about 350 hp.

    one of the the main functions of compression is to pack the fuel/air mix into a tight area for both fast effective ignition and to provide a mechanical advantage for the piston & rod assembly to push against the crank throw,as that mass in the combustion chamber burns and rapidly expands.

    lets look ast your question, given identical 350 displacement engines with flat top pistons and a comon .032 thick head gasket, a .023 deck and 5cc valve notches, heres what your going to see in STATIC COMPRESSION,as a result of combustion chamber changes


    keep in mind you want to stay at about 8:1-8.5:1 in DYNAMIC compression

    to run comon pump gas without getting into detonation
    that depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas


    calculators ... lator3.htm

    threads/info ... index.html ... index.html ... 0Time!.pdf
    Porting School #5 Identifying Primary Restrictions

    #5 Port Appraisal
    The first step toward more flow is identifying a flow restriction.

    David Vizard

    The small block Chevy head with it’s pushrod pinch point just in from the manifold face probably brings about more initial porting misconceptions than any other head. A novice looking at such a head almost immediately assumes that the pinch point must be the restriction stopping the engine from making much bigger hp numbers. The reality is far different and it sometimes takes a graphic example to convince a would-be porter otherwise.

    Granted there are a lot of aspects than we need to cover if the intent is to develop an optimal port for what ever performance application you have in mind. And before any of you over enthusiastic novice porters start bombarding me with questions on what will be down the road topics let me tell you - we will get there. But we have to start somewhere so let us begin by considering the magnitude of the task at hand – namely filling cylinders with an air fuel mixture up to high rpm. The following drawing should put things into prospective. When you realize the physical proportions of the elements involved achieving our goals don’t look to be quite as easy to achieve.

    The real point to note here is how small the intake valves are in relation to the volume of air that has to be drawn in to make just 400 hp. That is a figure that most of us relate to nothing more than a hot street 350. If the goal is 600 hp the task of filling the cylinders is even more daunting. As much as this looks to be a great illustration of the situation involved it does in reality fall short. Let us not forget that at any one moment in time in a V8 that 5 of the 8 valves are closed so in effect all the air has to pass through just 3 valves. Things are now looking really serious but it does not stop there. We also must take into account that valves open and close and that on average they are at half lift. If we now add this into the equation we can say that for all practical purposes all that air for 400 hp has to pass through the equivalent of just one and a half of the valves shown. So what does this all tell us? What it means is if you want to make real hp from your engine you had best be a real porter and know what you are doing – because it is hardly all a walk in the park!

    If you have now absorbed the implications of the above then it’s time to move an and establish just where in the induction/exhaust system the real restrictions lie. In an effort to put some numbers on it I did, many years ago, saw up a small block Chevy head and flow each individual section to get a better idea of the relative flow efficiencies of various parts of a port. Although I am using a small block Chevy port here as an example what we are looking at carries over to most ports. First let’s look at a typical production casting as per that shown below.

    This head has the valve at about what would be half lift for a sane performance street cam. This represents the average lift seen at the valve.

    Using a clay radius entry on each section (not shown in these drawings) the flow figures are seen. From these numbers it is obvious that the entry point A is not the prime restriction but the area at and around the valve seat.

    From the above drawings it appears that the point of greatest flow restriction is at the valve seat. This is actually the case and applies to both the intake and exhaust. The reality of the situation is that the most important and influential part of any cylinder head port is the part ½ inch above to ½ inch below the seat itself. From this we can see that any work we do to the head should start by shaping the before and after seat area such that it flows as effectively as possible.

    For the novice head porter the info just given could well save a lot of wasted time. Before even considering enlarging the pinch point area of the port (or any part of the main section of the port on any head for that matter) you should come to terms with the seat and bowl area. Reworking this is often termed ‘pocket porting’ but it can mean different things to different folk. Here, for every-ones benefit, is the GFN definition of pocket porting. It essentially implies the blending of the valve seat into the bowl area in a smooth and well rounded manner. In our case it also means tidying up the short side radius of the port so as to make the best of that. If you are doing a pocket port job then it also implies that the intake and exhaust valves have a blending form applied to them on the back face, and in the case of the exhaust, a radius on the front face. This plus a little chamber work pretty much constitutes a pocket port job. As to how effective it can be we have to consider what it was we started with. If it was a stock Ford or Chevy head prior to about 1990 the improvements can be quite substantial. In fact a pocket porting job well done can find about 2/3 of the extra air available from a basic full porting job but for about 1/3 of the expenditure in time and effort. This makes a pocket porting exercise a very effort effective deal. For later style heads such as the Chevy Vortec heads there is less to be gained from the intake although the exhaust responds well. These later heads are manufactured using a far more refined casting technique and, as a result, the factory leaves less on the table for the porter to find.

    In Porting School #6 we will continue our journey through the inlet flow processs in more detail and reveal some little known methods of identifying and minimizeing valve shrouding.

    David Vizard
  5. grumpyvette

    grumpyvette Administrator Staff Member

    ITs rather foolish to start with stock cast iron cylinder heads if your goals are over about 400hp with a sbc, use something like the 882 heads that are serviceable and with minor port work you'll get to that level of hp,but even the vortecs flow better, and might be a better choice ,if your looking for basic cheap transportation those heads work, but a great deal of an engines potential power lies in selecting the correct cylinder heads, if your thinking of building well over 400 hp Id surely look elsewhere, if your looking to exceed 400hp ID suggest the cheaper (yeah still expensive, but much better)aftermarket heads, that flow better. if your looking for a lot more your almost certainly going to need extensive and expensive port work or aftermarket cylinder heads.

    mid range options ... toview=sku

    better for peak HP
    , but the matching components get expensive fast ... toview=sku ... toview=sku ... toview=sku
    port size to displacement guide
  6. grumpyvette

    grumpyvette Administrator Staff Member

    what tends to make me crazy is guys that insist on running vortec or similar small port heads and a dual plane intake for max low rpm torque, when I or someone else builds thier engine, BUT ,who then come back and want thier 383-421 sbc to run the big hp/tq numbers and pull hard at 6000rpm and above where those small ports are far past there effective air flow limits
    Ive built some KILLER engines useing the 215cc and 230cc IRON EAGLE heads, TRICKFLOWS,BRODIX,AFR and SIMILAR larger port heads that made great torque in the low and mid ranges, a dual plane intake,with long runners and a 600cfm-750cfm carb helps, as does a cam thats designed for the midrange torque, and full length headers , with 1 5/8" primairies,its NOT the port size in the cylinder heads ALONE that determines the results! its the COMPLETE MATCHED COMBO and the thought that was put into makeing the components match the intended power curve, and matching the cars rear gear and stall speed to that power curve, sure you might be running slightly higher average rpms, to get the best power ,but youll be making a whole lot more power at the rear wheels too!
    if you want to get good mileage and decent torque and limit yourself to 1500rpm-3500rpm the small port vortec type heads work great on a 350,thats what G.M. spent the money researching the design to do! ,they are after all TRUCK HEADS!
    but increase the displacement to 383 or more and spin the engine to 6500rpm and they become a huge restriction!
    while a larger head can give up very little if anything down low in the rpm range but pull far bigger numbers on the hp/tq up higher in the rpm range simply because its still able to flow the necessary voluum of air the engine needs, G.M. knows that! but they also know that 90% plus of the time EMISSIONS and GAS MILEAGE and smooth just off idle low rpm torque is where most engines are used, so they build to fit MOST users expectations

    play with the calculator(above) youll soon see the vortec heads are designed for max tq at 3000rpm,and it takes a significantly larger head to make good power in the 5800--6400rpm range where a good race engine needs to operate
  7. grumpyvette

    grumpyvette Administrator Staff Member

    heres a bit of a comparison between common stock chevy heads vs a mild iron dart head, and yes DART and other manufacturers have much better heads available
    Chevy 882 Iron in stock form flow 206 int/145 ex
    -these are thin casting and very common cylinder heads

    this might help

    1) open throat to 85%-90% of valve size
    (2)cut a 4 angle seat with 45 degree angle .065-.075 wide where the valve seats and about .100 at 60 degrees below and a .030 wide 30 degree cut above and a 20 degree cut above that rolled and blended into the combustion chamber
    (3)blend the spark plug boss slightly and lay back the combustion chamber walls near the valves
    (4)narrow but dont shorten the valve guide
    (5) open and straiten and blend the upper two port corner edges along the port roof
    (6) gasket match to/with intake and raise the port roof slightly
    (7) back cut valves at 30 degrees
    (8) polish valve face and round outer edges slightly
    (9)polish combustion chamber surface and blend edges slightly
    (10) remove and smooth away all casting flash , keep the floor of the port slightly rough but the roof and walls smoothed but not polished.
    (11) use a head gasket to see the max you can open the combustion chamber walls
    (12) blend but don,t grind away the short side radias

    related useful info
    Last edited by a moderator: May 18, 2018
  8. grumpyvette

    grumpyvette Administrator Staff Member

    hey grumpy... Aluminum:a weak metal with an over exaggerate reputation.i.e:(aluminum cylinder-heads)
    example of over exaggerated reputation: Aluminum cylinder heads are better.

    your welcome to your OPINION, and free to run what you wish,but ID bet that opinion changes the first time you crack chunks off your cast iron cylinder heads, that you've got $1200 in port work done too and they get thrown in a dumpster as non-repairable, and yes all heads that are installed on a race engine will eventually get worn or damaged.
    a decent set of aluminum heads has several BIG advantages over cast iron, provided you use the correct coolant so corrosions not a problem.
    first like you stated
    (1)they are significantly lighter in weight
    (2) they are far easier to repair if damaged
    (3) they are far easier to weld, if they require modifications that require adding a bit of material.
    (4) they are easier to PORT or do machine work on.
    (5) they tend to transfer heat to the coolant far more efficiently
    (6) given equal compression ratios theres a slightly lower tendency to get into detonation

    [color=004040]Cast iron:A metal with a sleeper touch.a stronger,more efficient metal.i.e(cast iron cylinder-heads).cast iron cylinder-heads have been used on every thing from the first engines all the way up to high horsepower engines of today.

    look no matter what you say,aluminum heads are crap.sorry,thats facts.if not,then why when,cars and truck started being equiped with these kinds of heads from the factory,did the compression ration jump up and the same engine with cast iron heads make 15hp more?[/color]

    cast iron castings hold heat and transfers heat to the coolant noticeably slower, making cast iron heads more prone to detonation at any given compression ratio, the same reason aluminum heads can generally be used at a slightly higher compression ratio, and BTW, if both materials are run on very similar engines theres rarely a noticeable difference in hp, especially if the compression ratio on the aluminum head configuration is boosted in compression just a bit , or has a thermal coating in the combustion chamber to slow the heat loss rates,to run at equal pressure and heat levels
    there are more drawbacks about going to aluminum heads then i would care to deal with.the only positive thing is,yes they take weight off the front.
    BE AWARE, that theres a significant variation in spark plug location between different cylinder head designs,made by different manufacturers ,and theres both strait and angle plug heads and even the angle plug heads vary a good deal between designs, and many headers won,t work with a few cylinder heads in some applications so its almost mandatory that you call and talk too the tech support guys from both the cylinder head and headers manufacturers, to ask if any specific combo has a history of clearance issues BEFORE purchasing your headers or cylinder heads or both.

    reading material ... index.html ... index.html ... index.html ... sults.html ... index.html ... index.html

    the material the heads are manufactured from will have a big effect on their ability to dissipate heat quickly from the combustion chamber,increasing compression tends to increase the heat generated during combustion, aluminum transfers heat much faster than iron into the coolant, and its that factor more than most that forces you to reduce the effective compression slightly compared to an aluminum head IF your getting into the detonation range due to heat, of combustion, compression,and the ignition advance
    the surface finish and shape of the combustion chamber and piston dome,coolant temp. air temp,the combustion chambers tumble and swirl, the fuel octane, the quench/squish distance, spark plug heat range, also will effect your engines tendency to reach detonation
    as a general rule on pump gas the temp in the combustion chamber is the limiting factor on reaching detonation.

    short answer, aluminum tends to allow you to run about 1/2 point more effective compression, IE, if iron heads get into detonation at 10:1 ALUMINUM might ALLOW YOU TO RUN 10.3-10.4:1 BEFORE GETTING INTO DETONATION, BUT ON THE PLUS SIDE AT LEAST IN THEORY IRON HEADS AT ANY GIVEN CPR WILL HAVE A SLIGHT ADVANTAGE IN HP
    but in my real world testing the difference is much closer almost non-existent
    the main advantage I see in aluminum heads is lighter weight and their much easier to repair when damaged

    [​IMG] ... index.html Compression Tech.htm
  9. grumpyvette

    grumpyvette Administrator Staff Member ... index.html ... CH353-ES-1 ... index.html ... 857C0.aspx ... rHead.aspx

    read thru this, its basically an engine build where they use all the tricks to get a fairly stock set of mildly reworked large port vortec heads , with a much improved valve train to produce thier max power

    now those heads, intake and a milder roller cam, would be more useful to most of us ,on a slightly less exotic 406 or 383 SBC combo

    Vortec Bow-Tie Brief
    There are two versions of the new GM Performance Parts Vortec Bow-Tie cylinder heads: This one, PN 25534371 (bare) and PN 25534431 (complete), with the larger ports, and another with smaller ports, PN 25534351 (bare) and PN 25534421 (complete) with 185 and 65cc volume, otherwise, the architecture and improvements over the L31 design are the same. We will test the smaller version very soon in a dynamometer exercise. We were able to get an exclusive look at the big-port heads just as they were used in a NASCAR-type application.

    Out of the box, they feature revised intake and exhaust ports and are machined for a 2-inch intake and 1.55-inch exhaust valves. The deck surface is 0.045-inch thicker than the L31s, and it has 65cc combustion chambers, a 206cc intake, and 77cc exhaust ports (see Flow Chart). The head is also machined for 3/8-inch screw-in rocker studs and a large valvespring pocket, and it will accept up to a 0.530-inch lift camshaft without modification. These castings are identified by the Bow-Tie logo below the exhaust port and the Vortec logo on top of the intake port area. The GM logo is also cast into the bottom of the intake port runners.

    All concerned will be delighted to hear that the head includes intake manifold mounting holes for both early-model six-bolt and late-model four-bolt Vortec design. Mandated GM intake manifolds include a raised runner-type PN 10051103 (six-bolt type) or Vortec design PNs 12366573, 12496820, 12496821, 12496822, and 12499371 (four-bolt type). Though production cylinder head and intake manifold gaskets are acceptable, the hot squeal is Fel-Pro (PN 1142 for the MLS and PN 1289 for the intake). As per Scoggin-Dickey, pricing is: small port 4421 complete, $499.95; small port 4351 bare, $269.25; large port 25534431 complete, $539.95; and large port 25534371 bare, $293.25. ... 534431.htm ... dID=104477

    BTW if your looking into aftermarket performance cylinder heads for the BIG BLOCK CHEVY, the blocks have different coolant passage lay outs, and require matched heads and head gaskets , but check with the manufacturer of the cylinder heads, many of the better aftermarket big block heads have been modified with a larger sealing surface areas and relocated coolant passage locations and coolant passage shapes so that they can be used with any and all the generations of the big block blocks, if the correct gaskets are used, simply because the manufacturers found that to be far easier than stocking several different castings for basically similar applications
  10. grumpyvette

    grumpyvette Administrator Staff Member ... A11-P1.htm ... A11-P2.htm ... A11-P3.htm ... A11-P4.htm ... A11-P5.htm ... A11-P6.htm ... A11-P7.htm

    look this is not a guessing game (selecting the correct port size)you select and verify the correct port size and cross sectional area,using know calculations, valve diam. and flow rate for the application, verify clearances in the valve train,and that the cam and valve train are compatible for the intended rpm band and stress levels,
    you match the cams intended rpm and power band to the displacement and compression ratio,make sure the valve curtain are exceeds the port cross section slightly , select the cam lift and duration to maximize the port flow,potential, select headers designed to operate in the same power band, select a drive train that keeps the engine in that power band most of the time.



    if your thinking about using an older set of fuelie heads, it depends mostly on the condition of the heads,(remember fuelies are on average over 40 plus years old)and on both WHICH fuelie heads they are, and the valve sizes,if they are not 2.02/1.6(if your willing to do minor port, bowl and combustion chamber mods like un-shrouding valves) Id suggest going vortec.

    and if your going to have the vortec compatible parts like valve covers, rockers, intake, etc. but in almost every case the VORTEC HEADS will produce slightly better power, unless you do those mods to the fuelie heads

    typical reworked fuelie


    keep in mind the average fuelie head has a smaller 155cc port than the typical vortec at about 170cc, and the higher port angle on the vortec heads flows better ... l#GM%20LT4



    remember this chart?

  11. grumpyvette

    grumpyvette Administrator Staff Member

    looking to make killer power without ALL the expensive mods like shaft rockers and offset lifters etc, these heads might be what your looking for.. ... toview=sku

    The BRODIX 18X offers the best of both worlds, 18° horsepower without using expensive shaft rockers or offset lifters.
    This head offers a dramatic horsepower increase over the 23° cylinder head.
    Several advantages of the 18X are intake ports that flow over 320 cfm out of the box, an intake valve size of 2.140, raised intake ports, and shallow combustion chambers. The 18X is an excellent choice for the budget-minded racer who wants to go fast.
    heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes


    sure its expensive, but compared to some of the options its a screaming deal once you total up all the mandatory OTHER parts it takes to correctly run THOSE other heads.....these brodix heads should easily support 600 plus hp on a correctly built, high compression roller cam, 355-427 sbc
    just keep in mind a great deal of an engines power potential lies in its head flow, cam timing,displacement and compression ratio, and selecting great heads will usually be money very well spent
    Last edited by a moderator: Dec 12, 2017
  12. grumpyvette

    grumpyvette Administrator Staff Member

    Head flow & results on a 383

    CHEVY high performance mag for aug 2006 did an interesting comparison between eight different cylinder heads available for $1000 or less.
    While youll need to read the article to get all the data, I found it very interesting.
    The articles called
    and it starts on pg 22

    Heres a few differant different articles ... _0401_imp/ ... 6_thunder/ ... ewall.html

    the main factors you should notice is that ENGINE DISPLACEMENT MATTER TO THE RESULTS, port size(cc)IE the difference between a 175cc to a 230cc) has far LESS effect on the power curve and peak power that the AIR FLOW, and that flow rates measured at lifts above where the CAM reaches its max lift, and has little to no effect on the power curve, the cams duration and lift and LCA effect the results, the combustion chamber design and valve size DOES matter.
    And the intake and exhaust design and flow rates DO EFFECT the power curve.

    STANDARD OEM vortec heads have approximately a 170cc port volume and are designed to maximize torque in a 350 at about 4500rpm, they ARE generally slightly better than the older fuelie heads but there are much better heads currently available.
    Theres no question that the standard vortec head flows better at near 230cfm than the previous fuelie and corvette heads that flowed less than 210cc in stock form
    but theres a dozen or more aftermarket heads that flow well in excess of 250-280cfm, at reasonable valve lift ranges

    a couple hours spent reading links could save you a ton of money and work ... eads1.html ... -23-degree ... minum.aspx ... heads.html

    you might want to read thru these links, a couple hours reading could save you a good deal of time and money










  13. grumpyvette

    grumpyvette Administrator Staff Member

    this question comes up frequently
    "If I were to order a set of heads from summit or who ever and I bought the bare heads rather than a set that were assembled would I have to send them to the machine shop for work or could I buy the valves, springs studs etc and do it myself? "


    Ive seen several sets of bare heads that required HUNDERED$ of dollars in machine work, like doing a 3-5 angle valve job, clearancing the push rod holes,decking the surfaces,combustion chamber mods, spring pockets needed machining , stud pads needed truing and threading for the studs,etc. before valves, springs, rocker studs, push rod guide plates,valve seals ETC. could be installed.
    IVE also seen heads that were basically ready for assembly as the came from the box!
    ALOT of detailed questions need to be asked before going that route....
    BUT ILL also point out that in many cases you'll save a great deal of money, not paying for parts that you won,t be useing and get far better quality components, and be much surer the clearances are correct if you do it yourself with components you select.
    you generally won,t get titanium retainers and valves that are .100"-.250" longer and the better quality beehive springs, or similar components and clearance work in an off the shelf cylinder head.
    naturally it helps to start with a decent quality casting from a major manufactuer, so components are easily found that match the application.








    ID suggest you select from heads from these sources ... 4294867081 ... main.shtml

    Last edited by a moderator: Feb 11, 2016
  14. grumpyvette

    grumpyvette Administrator Staff Member

    FOR those guys thinking they can quickly and cheaply get 500hp from a basically stock 350 sbc........IM going to break the bad news....stock heads are a huge restriction as is basically most of the stock components,to build a 450-500hp small block chevy the block and water pump are usually all thats used in stock condition,
    yes IM fully aware, that if you were like most kids growing up in the 1960-1980,s in America, the older kid next door when you were younger threw a 4 barrel intake, headers and a off track Z28 cam in his camaro and it loped like a dragster and was scary fast when you were younger........yeah! it was faster than stock,but probably no where close to the 500hp he bragged about!
    IF your looking to keep cost low the lower cost options are between the VORTEC, L98 and older fuelie heads, in many cases, if your given a choice between the l98 aluminum heads of the C4 corvettes heads they are generally moderate to poor performers,compared to vortecs or properly ported fuelies, almost any PROPERLY PORTED set of fuelie heads should out perform the stock or moderately ported l98 heads from what I see., but remember fuelie heads are 40 plus year old technology even the vortec heads usually out perform BOTH in stock form...but if you have port work done to the fuelie heads ID strongly suspect they will out perform the stock L98 heads, but keep in mind the later version aluminum l98 heads weigh less, are easier to repair and allow use of lower octane fuel, so theres other factors to think about

    read thru this

    ID suggest you start by reading thru these ... 714&sr=8-2 ... 799&sr=8-7 ... 894&sr=8-2


    viewtopic.php?f=69&t=780 ... id/131229/ ... w-230.html

    "swapping from rectangle to oval heads on your big block is a sure way to increase torque"

    I saw that posted on a different site and I had to smile, its obvious that that might be true on some applications but its not necessarily even close to valid in all cases,and the individual cylinder heads port design you select, has a bigger effect than similar sized oval vs rectangle port heads, port shape, you can very easily make more total torque, and usually over a wider rpm band with lets say an AFR or BRODIX 300cc-315cc head than a 253-275cc oval port head if your willing to match the rest of the combo to take full advantage of the heads potential. yes its true the smaller heads faster port speeds should produce more efficient volumetric efficiency lower in the rpm band, but that same factor tends to limit the upper rpm potential
    your engines torque curve is more the result of displacement, compression,ratio,selected cam timing and both header design (scavenging) and intake design (SINGLE vs DUAL PLANE ETC.)than just port cross sectional area alone, and if your wearing valve guides the valve train geometry and clearances, and lubrication system, and the oil used in it, and your valve spring rates and seals need to be carefully checked and a rocker stud girdle and roller rockers used
    and port cross sectional area and flow numbers have a larger effect than port shape alone
    naturally you'll need to match the port cross sectional area, length, and plenum to the intended displacement and rpm band, and cam timing, but just assuming a swap from rectangular port to oval will always result in more torque will not always be true over the whole power band, especially if the rest of the combos designed for a totally different rpm band than the heads you've selected.
    tweaks like tuned merge collectors, and slightly different cam timing and intake swaps can get a great deal more of the torque potential from a slightly different port size,and there are calculators you can use to find a limited selection of choices,in header length, diam., collector, intake port length and cross section and runner length, plenum size, cam timing and valve size to look thru.. too narrow your search for the best match to your application vs just guessing and swapping parts till you think you've got it correct
  15. grumpyvette

    grumpyvette Administrator Staff Member

    INTERESTING LS head info ... index.html ... earch.html ... /dart.html ... brock.html ... ports.html ... s/tfs.html

    ir Flow Research Kook's Custom Headers
    59 Cleveland Ave.
    North Bayshore
    NY 11706
    Dart Machinery
    353 Oliver St.
    MI 48084
    Livernois Motorsports

    Edelbrock Corporation Headquarters
    2700 California St., Dept. CHP
    CA 90503

    Trick Flow Specialties
    1248 Southeast Ave
    OH 44278
  16. procketus

    procketus New Member

    Hi Grumpy,
    This is related to my post at DC about swapping heads. I had mentioned a friend had a longblock for sale. looked at it today but it is a 305. Pulled the valve cover and the heads are 14014416. Now my question is, with the smaller combustion chamber(58cc I think) and the smaller valves(1.84 int, 1.5exh) would these not perform better? I do remember long ago, about 20 yrs, guys talking about putting these heads on 350 and they ran better. But before I commit to buying these I would like your opinion. If they improve performance great if not I'll pass on them.

    Btw, I did replace the bad stud with a replacement screw in type.

    Would also like to mention you have a great site here, lot of good info..

  17. grumpyvette

    grumpyvette Administrator Staff Member

    thanks for the praise, please tell others,

    as to the heads the answer depends on what your trying to do, if its just for basic transportation and your not after power those heads are fine as they will without doubt raise the off idle and low range torque due to higher compression, but they will hurt mid and upper rpm power as they don,t breath well.

    NEW/HEADS, you should NOT just bolt them on!

    now Ill probably tick some guys off here, but I see enought heads come thru the shop to point out a common problem, and its NOT limited to one or a couple manufacturers, Ive seen it on nearly every brand and type of cylinder head!, what Im referring to is bits of casting flash, bits of aluminum or cast iron chips from machine work or sloppy assembly, burred threads, threads that are not cleanly cut,ETC. on new out of the box cylinder heads, I won,t name brands BUT some of the top names have bits of aluminum chips/dust/crud left in the ports in as shipped heads and dis assembly and use of a stiff tooth brush, high pressure air and carb cleaner spray along with reassembly with the proper lubricants and running a tap thru threads and cleaning all machined surfaces with solvent,is almost mandatory if your don,t want bits of crud washing around in the engine during first starting the engine. it sure doesn,t hurt to check the spring bind and other clearances, and that the valve seals are correctly installed either
    IM sure the manufacturers used a high pressure air hose to blow out the ports and water passages, but theres commonly some crud remaining so inspect carefully, and clean those new heads BEFORE installing them
    , yes the cheaper brands seem more prone to this problem but even the best brands are commonly seen to be received in less than stellar condition, and need some basic clean-up

    BTW, one of these tools comes in handy during the inspection process

  18. grumpyvette

    grumpyvette Administrator Staff Member

    I get asked all the time which heads to buy, thats a bit like asking me to select your next girl friend without you telling me what factors are important to you.
    generally cost is a huge factor and most of us can,t throw buckets of money at problems
    most of the stock sbc heads are less than impressive, if your looking to build a killer hot rod engine and aftermarket suppliers like
    airflow research,

    can supply you with valid options, but don,t get extremely cheap, thinking your current factory heads can be mildly ported to make as much power as the aftermarket castings can,, thats almost always a waste of time and cash, your heads and cam have a huge effect on your engines potential power produced.
    assuming your building a common 355-406 sbc and youve got at least the block and crank,to start with,Id suggest you print out a realistic budget for your project and spend 1/3-1/2 on the engine in the heads and cam.
    these several threads on matching the port size to the intended use and which intake to buy etc. take the time to do some research before you start writing checks







  19. grumpyvette

    grumpyvette Administrator Staff Member ... -shootout/
    heres a rather interesting comparison test of cheaper SBC cylinder heads,
    notice the SMALL PORT VORTEC HEAD is rather LOW on the list for performance, but the standard 170cc vortec head was designed to maximize low and mid rpm torque not peak power
    and some heads were at a disadvantage due to the cam , intake and headers selected to test did not maximize the flow potential.
    Cylinder Pressure Note: youll generally want to try hard to maximize the useable compression as the higher the compression before you get into detonation the more efficiently the fuel can be burnt and the more torque the engine can produce, if limited to pump high test 92-93 octane fuel,165 psi # of cylinder pressure is about the best cylinder pressure for Iron heads with 92-93 octane, using pure un-ethanol laced fuel, gasoline. while the faster heat transfer rate of aluminum cylinder heads will usually allow 190psi # as the upper limit or best for aluminum heads.
    before you spend a good deal of money porting and un-shrouding any iron cylinder heads, keep in mind aluminum heads are easily repaired in a skilled and experienced automotive machine shop thats equipped to do those repairs but damaged iron cylinder heads are either much harder to repair or good door stops

    Automotive Racing Products; 800/826-3045;

    Dart Machinery; 248/362-1188;

    Edelbrock; 310/781-2222;

    Federal-Mogul; 248/354-7700;

    Harland Sharp; 440/238-3260;

    Jegs; 800/345-4545;

    Jim Grubbs Motorsports; 661/257-0101

    Patriot Performance; 888/462-8276;

    Scoggin-Dickey Parts Center; 800/456-0211;

    Speedway Motors; 402/474-4411;

    Summit Racing; 800/230-3030;

    Tri-State Cylinder Head (Flo-Tek); 800/270-0095;



    viewtopic.php?f=52&t=401 ... cc-sbc.php ... -23-degree


    viewtopic.php?f=52&t=9811 ... cc-sbc.php ... cc-sbc.php

    any of the performer or performer rpm heads will produce better power than the vortec heads on the 383 sbc is matched to that existing intake and nearly any reasonable cam selection, plus run cooler and weight less and be easier to repair or port if thats ever needed, that does not necessarily make them the only or best available option.

    Last edited by a moderator: Oct 10, 2017
  20. philly

    philly solid fixture here in the forum

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