another 496bbc

The Higher the Static compression with a Race Cam the more bottom end torque that is present.

Has to run on 110 motor octane race gas.

100 LL Av gas. Timing pulled back 4 degrees.
Also have to run cold Racing Spark plugs with a Race Cam.
Need to constant Rev up to clean the spark plugs off.
Or they load up fuel foul out.
Make Noise.
Once up to highway speed its Ok.
first thing Im forced to point out is theres several completely different 496 BBC engine build links, contained in this and linked related threads...
most are not designed as racing engine, those would have 12.5:1-13.7:1 compression, almost always a hydraulic or solid roller cam
and perhaps a tunnel ram intake or stack injection, maybe even super charged, etc.
featuring parts lists and dyno results in this thread,
can be rather useful for comparing potential build ideas.
next the whole original concept was to point out the differences in the builds and results not to say any one particular build was a prime example of what to build.
I started out with the build having the 265cc oval ports as a reasonable mid power range as a base line , not as the ideal build,
I also wanted you and anyone reading through the linked info to see how increases in port size compression and cam duration in similar displacement
(496 CID in most cases) engines tended to cause different power curves.
500hp-600 hp will be rather common,
personally Ive found the 280cc-300cc oval port heads and the 305cc-315cc rectangle port heads on the BBC engines to be about ideal,
PROVIDED the compression and cam timing choices are carefully matched to maximize the head ports flow potential.
generally if your going to build a hotter street performance engine for a daily transportation used with commonly available pump octane gas,
perhaps an auto trans with a 2700 stall converter and 3.36-3.73:1 rear gears , and a decent dual plane intake,in what is basically fast daily transportation, in an older muscle car,
you want a 9:1-9.5:1 compression, a set of 280 cc-290 cc oval port heads and a cam duration in the 235-245 @.050 lift range and lift in the .580-.630 range flat tappet or hydraulic roller.
if you want increased performance and are willing to sacrifice some drive ability,
you might want to select a bit more compression, IE 10.0-10.5:1
the smaller rectangle port 300cc-315cc heads , a single plane intake , 3.73:1-4.11:1 rear gears
at least a 3000 rpm stall converter and a cam with about a 245-250 duration @.050 lift range, and lift in the .610-.715 range, almost always a hydraulic or solid roller, 600 hp-700 hp or a bit more is available.
assuming the proper headers exhaust and carb sizes are selected the difference in power could easily be 60-120 hp or more difference
between the two basic concepts and obviously a loss in easy street driveability in bumper to bumper traffic, you simply,
e make choices based on what your willing to put up with and what you want to trade off in driveability to gain performance.
I see, forest meet trees
couldn't see the forest for the trees,
If that makes sense.
I got caught up on cam duration vs. Intake and compression , and bring that combo in 103 intake center line I've picked up that this thing will more than likely have a rougher idle then say 108 intake center line. But I see these are just examples now
Not necessarily the best way, just a way

Build a brute 600-horse Chevy 496ci stroker
Written by Jim Smart on November 1, 2018

What can you do with a big-block Chevy that hasn’t been done before? Well, for one thing you find ways of making it more distinctive than the rest. It doesn’t have to be the most powerful big-block Chevy ever done because there’s always someone with a pinch more poop. It just has to be that sweet combination of streetable performance with durability and an attitude. You want brute torque for a spine-decalcifying snap at the traffic light or at the dragstrip yet civilized cruiseability on the open road. This engine courts the edges of both streetability and a racing engine.

With 496 ci of displacement on hand coupled with 4.250 inches of stroke and 6.385-inch-long rods for generous dwell time are the bones necessary to make a classic Chevelle, Camaro, or Nova rock. Intimidating at a traffic light. Rock and roll time at the track. We’re working with Gregg Jacobson of PHD Speedcenter in Bakersfield, California, who understands what it takes to build real horsepower and torque into a vintage mill.

Scat stroker kits are available with either a high-end forged 4340 crankshaft or Scat’s Series 9000 cast crankshaft and I- or H-beam connecting rods with either 7/16- or 3/8-inch cap screw rod bolts. For maximum durability Scat includes King, Federal Mogul (Speed Pro), or Clevite 77 rod and main bearings depending upon the application—with pistons and rings from SRP/JE, Ross, KB, Mahle, Diamond, and Probe. Ordering a Scat stroker kit from Summit Racing Equipment means you’re getting solid reliability for your Chevy big-block project.


We’re working with a Chevrolet 454 four-bolt main truck block (PN 14015445), which is a good foundation for the kind of power we want to make. It has been cleaned and Magnafluxed for cracks. Chevrolet produced this block casting from 1978-1990. Not all PN 14015445 blocks are four-bolt main. Make sure you’ve found a four-bolt main block before plunking down the cash. This is a brute block that can handle 500-plus horsepower.

Gregg Jacobson of PHD Speedcenter tells us block prep includes a full program of machinework, including deburring, milling the decks, line bore, piston-matched boring and honing, and honing the lifter bores for good oil control. Jacobson uses GE Glyptal coating on iron surfaces to both seal the iron and improve oil return flow.

Oil galley passages have been chased, tapped, and plugged for good oiling system security. You can never clean oil galleys even because there are always traces of debris. This is a good practice for any engine build in order to maintain oiling system security.

Jacobson stresses proper installation of the two-piece rear main seal, which is a heavy-duty Fel-Pro seal. The seal lip must be installed toward the crankshaft, which keeps the seal lip against the crank journal. Jacobson uses Permatex’s The Right Stuff between the seal and block, with a small dab at each end. Seal tips are staggered away from the main cap parting lines to prevent leakage.

For a mean street/strip demeanor, Jacobson has opted for the COMP Cams mechanical roller cam with 110-degree lobe centers (PN 11-772-8) and a lot of lift and duration for deep breathing at high rpm. You get a lumpy idle along with a good broad torque curve from 3,000-7,000 rpm. Jacobson was anticipating 600 hp and comparable torque.

Because Jacobson thrives on durability, he opted for a Scat 4340 steel crank with a 4.250-inch stroke and 6.385-inch H-beam rods topped with Mahle forged pistons with a mild dome. The result is 496 ci and a tremendous amount of torque from the 4.250-inch stroke. These rods offer a good rod ratio and allow plenty of dwell time and cylinder fill/scavenge time at each end of the bore.

PHD Speedcenter’s piston prep includes the installation of plasma moly iron rings on top, cast rings next—positioning the endgaps at 90-degree intervals. Rings and pistons are coated with engine assembly lube to ensure a nice, wet startup. When Jacobson fires this engine on the dyno, he will do a break-in cycle to seat rings and bearings before doing power verification pulls.

Once all eight pistons are in their bores, Jacobson will check deck and compression-height to get an accurate assessment of what he has for compression ratio. Compression ratio was expected to be 10.0:1 for use with pump gas.

Connecting rod bolt torque is 63 ft-lb in one-third values one cap at a time. The rotating assembly is checked for freedom of movement as Jacobson torques rod bolts.

Crankshaft endplay is checked and should of 0.004-0.008 inch in a high-performance application.

When you’re building a street/strip big-block Chevy you have the option of ARP studded main caps, which is suggested for better bottom-end security. You may also go with ARP main cap bolts like Jacobson has here, which provide a much better level of main cap security than stock bolts. Main studs keep caps from wandering much better than bolts.

Because we’ve gone with a Scat stroker kit, the very first order of business was the mockup phase, which we did not photograph, but will explain here. A mockup pre-assembly phase should be performed early on without piston rings installed to make sure rods, bolts, and counterweights clear the block and oil pump.

Jacobson opted for the COMP Cams adjustable double-roller billet timing set (PN 8110) from Summit Racing Equipment for this 496 project, which enables him to adjust valve timing quickly and easily.

This close-up view of the adjustable billet cam sprocket demonstrates how easy it is to adjust valve timing.

We’re framing in the adjustable billet timing set with the COMP Cams three-piece aluminum timing cover (PN 312) from Summit Racing Equipment. Cool thing about this timing cover is access to the adjustable timing sprocket.

True top dead center and cam specifications are checked prior to the cylinder heads being installed. We found our cam to be spot-on with the cam card.

The cam button is installed next, which will keep the cam stabilized.

Cam sprocket bolts get Permatex thread locker and are torqued to 20 ft-lb.

With the COMP Cams three-piece cam cover installed, Jacobson checks camshaft endplay, which should always be checked. That’s what’s good about this timing cover. It enables you to check endplay with the cover on.

When we first saw these Mahle pistons, we were convinced this engine sported a lot of compression. However, the Brodix heads have large 119cc chambers, which have been massaged to 123 cc. Compression ratio is a mild 10.3:1 for operation with pump gas.

Jacobson is going with Fel-Pro Permatorque head gaskets from Summit Racing Equipment. Although they say these head gaskets don’t require a retorque Jacobson gives them a retorque anyway for extra added measure after the initial fire-up. Jacobson stresses clean mating surfaces because even the tiniest debris can cause leakage.

Jacobson likes the Super Damper from ATI. It is SFI rated and delivers smooth function at all rpm ranges. The Super Damper’s primary purpose is to act as a crankshaft shock absorber at the end of the crank to absorb crank twist.

These Brodix Race-Rite Rectangular-Port cylinder heads (PN RR BBR) are an easy bolt-on for virtually any big-block Chevy. They bolt right in place of the stock iron heads without special modifications or piston changes.

Jacobson performed some of his own custom port and chamber work on these Brodix heads to reduce turbulence and eliminate hot spots.

With the Fel-Pro Permatorque head gaskets in place, Jacobson seats each of the Brodix heads. Jacobson doesn’t cut corners when it comes to valvetrain components. He has specified COMP pushrod guides with ARP 7/16-inch rocker arm studs.

Jacobson has opted for a Speed Pro high-volume oil pump along with a Moroso deep-sump pan and pick-up to ensure abundant volume at high rpm.

We like the COMP valvetrain components encompassing Pro Magnum full roller rockers, which have been properly adjusted to 0.016-inch intake and 0.018-inch exhaust. Valvetrain geometry has been checked and confirmed using the correct length one-piece 0.080-inch thick-wall COMP Cams pushrods.

Our completed 496ci stroker looks sharp.

PHD Speedcenter has the 496 on a run stand for that initial fire-up to check vitals. Jacobson expects to see 600 hp at 6,500 rpm and nearly 600 lb-ft of torque at 5,000. That’s a 950-cfm Holley 0-80496-1 carburetor atop an Edelbrock Perfor
Initial Goals were reached Grumpy.

Gets expensive for further HP wants.
Been watching in race groups what 400-500 cfm heads can do & be streetable yet Chevy BB & Pontiac V8.
Jury is still out.

10.8 compression
243/249 cam duration
110 lca
.640 lift
Edelbrock air gap intake
2.25 intake and 1.88" exhaust valves
294 cc rectangle port brodix heads

I think he left a bit of power on the table using the smaller ports , a similar 310cc-320cc head may have proven a bit better above 4600 rpm



Big-Block Chevy OE And Aftermarket Block Variants

Generation Gap: Big-Block Chevy OE And Aftermarket Block Variants By GREG ACOSTA AUGUST 07, 2018 When it comes to big-block engines, there are quite a few variants across multiple manufacturers. However, when you hear the words “big block” with no other qualifier, there is one engine that...
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Big Block Cylinder Heads - Big-Block Cylinder Head Test
You Don't Need Sewer-Sized Intake Ports To Make 600 Hp With A 496ci Rat Motor As We Discovered In Our. . .

Jeff Smithwriter
Mar 1, 2008
'There's something about big-block Chevys that demands big cylinder heads. Maybe it's some sort of deep, genetic, missing-DNA-link thing between car crafters and Chevy Rat motors that insists on monstrous, rectangle-port cylinder heads. It's like some kind of baritone inner voice that won't be content with anything less than massive 360cc intake port heads on a 396.

We learned long ago not to listen to that caveman voice. Instead, we decided to look into how much power we could extract from a set of oval ports. That led us to stacking up all the available aluminum oval-port heads on a Rat and pushing 'em hard on the dyno. For a testbed, we used our existing cast-cranked 496 Rat motor built back in the Mar. '07 issue with plenty of displacement to really challenge these heads. We also included a set of production iron peanut-port heads just to see how they would do as a baseline. We really wanted a set of true iron oval ports, but we couldn't find any that hadn't already been ported. We also tamed the camshaft with a hydraulic roller so we wouldn't have to spin the engine as high to get the peak horsepower numbers. The results of this shootout were more than a little surprising. But be sure to read this entire story, not just glance at the power numbers, because we evaluated these heads in a bunch of interesting ways. Taken as a whole, the oval-port Rat market offers heads that are a lot stronger than you might think.

We tested a total of five oval-port big-block Chevy heads using our 496 on the Westech SuperFlow dyno just to see who came out on top. The results were amazingly close.
The MuleIf you recall, we built a 496ci Rat in the Mar. '07 issue that made a stout 707 hp on pump gas with a set of as-cast 305cc AFR rectangle-port heads and a big Comp mechanical roller cam. We had to twist that combination up to 6,600 rpm to achieve that power, which created more than a few Internet blog predictions of imminent engine failure focused on the cast crank and stock rods. Despite those doomsday prognostications, the engine is still very much alive even after this latest thrashing. But acknowledging those realities, we know it's just tempting fate to continue to spin this thing that fast.

To remain consistent with a conservative oval-port street concept, we decided to pull back on the cam timing to keep the peak horsepower below 6,000 rpm. This milder Comp Cams hydraulic roller cam timing is also a better fit with the entire oval-port package, including the Edelbrock RPM Air-Gap dual-plane intake manifold and 850-cfm Barry Grant carburetor. If peak horsepower had been the goal, we would have chosen any one of many single-plane intakes that would have easily kicked it up over 600 hp. Taken as a whole, this engine package turned out to be extremely successful considering that the engine idles at 950 rpm with 12 to 13 inches of manifold vacuum and offers tire-shredding torque. That idle quality is also more than enough to support power brakes and perhaps even an A/C compressor. We'd call that very streetable.

Cam: Comp Cams XE274HR-12 Hydraulic Roller
Advertised Duration Lift Lobe
Duration @ 0.050 (inches) Separation
Edelbrock HeadsThe Edelbrock Performer RPM oval ports are an interesting mix within the collection of aftermarket aluminum oval-port heads. They offer the largest intake-port volume of 290 cc with the smallest 2.19-inch intake valve. Among the specs we list for each head is the intake port cross-sectional area. We measured each of the five heads in the same basic place in the intake port to determine the smallest cross-sectional area. This dimension, in square inches, is intended to give you an idea of which head will generate the highest intake velocity based on size. A smaller intake-port cross-section will generate a higher intake-flow velocity while larger ports will experience slower velocities. Intake-port velocity (up to a point) has been shown to have a positive effect on cylinder filling, which results in better power. The Edelbrock's intake-flow numbers are decent, although not on a par with the other three aluminum heads, and still performed well despite having the largest intake-port cross-sectional area number.

Edelbrock has always offered excellent castings and competitive flow numbers for a very affordable price. This particular big-block part number comes with steel retainers and springs designed for a flat-tappet cam. To make the test fair, we changed to a set of Comp hydraulic roller springs and titanium retainers. These changes are not reflected in the price of the heads.
Another important consideration is that these heads rely on a stock exhaust-port exit position, which helps with header fitment. As we'll see in the dyno testing, the Edelbrock heads performed well in the horsepower test even though they did not win when evaluated strictly on torque and horsepower. But add in price and suddenly these heads are players, since they are the least expensive of all the aluminum heads we tested. Check out our dollar-per-horsepower evaluation and see if you agree that the Edelbrock heads make excellent fiscal sense.

Edelbrock Performer RPM-O "Roval"
2.19/1.88 valves
110cc chamber
Intake port volume: 290 cc
Stock location exhaust port
Intake cross-section: 3.07 sq. in.
PN 60479

Valve Intake Exhaust E/I
Lift (no pipe)
0. 100 66 58 88%
0. 200 135 126 93%
0. 300 196 149 76%
0.400 240 171 71%
0.500 264 189 71%
0. 600 281 203 72%
Dart Heads
These are the newest castings amid the oval-port contenders. Clearly Dart was after serious performance since it fitted these 275cc intake ports with 2.25-inch intake valves. Only the TFS heads with 2.30-inch intakes are larger. From a port cross-sectional area standpoint, the Darts are the largest of all the heads we tested, which might have contributed to their overall torque curve performance. One other aspect of these heads that does not show up on the flow numbers is Dart's emphasis on wet-flow development work.

The Dart 275 heads not only have strong intake-port flow numbers, but also offer some of the best exhaust flow numbers in this test. That superior flow can be partially attributed to the 0.300-inch raised exhaust-port exit point.
Dart also raised the exhaust-port exit 0.300 inch, which is a major reason the high-lift exhaust-flow numbers are so strong. What's interesting is that both the Dart and TFS heads offer a 0.300-inch raised exhaust port and that both the Dart and TFS heads' exhaust-port flow numbers make a significant jump at the higher valve lift, virtually duplicating each other as seen on the exhaust-port flow charts.

Dart 275 Oval Port2.25/1.88 valves119cc chamberIntake port volume: 275 ccRaised exhaust port: 0.300 inchIntake cross-section: 3.26 sq. in.PN 19000112

Valve Intake Exhaust E/I
Lift (no pipe)
0.100 68 68 100%
0.200 151 115 76%
TFS HeadsIf you look at the flow curves, the TFS and Dart intake-flow numbers virtually overlap throughout the entire flow curve on both the intake and exhaust, which is surprising. Despite this, there are a couple of items that differentiate the TFS heads. First, the TFS intake port has the smallest cross-sectional area of all the aftermarket heads at 2.84 square inches, while the Dart has the largest by a wide margin. The second point is the raised exhaust port, which creates excellent exhaust flow numbers that would probably benefit from a single-pattern camshaft design.

The TFS heads do push the exhaust port up 0.300 inch (left) compared to the stock production big-block Chevy position. This is the main reason that the TFS heads have such strong exhaust-port flow numbers at the higher-valve-lift positions.
TFS Oval Port2.300/1.88 valves113cc chamberIntake-port volume: 280 ccExhaust port raised 0.300 inchIntake cross-section: 2.84 sq. in.PN 41300002

Valve Intake Exhaust E/I
Lift (w/ pipe)
0.100 69 61 88%
0.200 141 126 89%
E/I is the exhaust-to-intake flow relationship expressed as a percentage.

Brodix Heads
The Brodix Race-Rite oval-port heads are an interesting approach. When we first flow-tested these heads, we were impressed with their out-of-the-box performance. Then when the idea for a test came along, Brodix offered a set of CNC-machined chamber versions that we didn't have time to flow-test. According to Brodix's Web site, this chamber mod should be worth roughly 4-5 cfm across the entire valve-lift curve. This also adds another $225 to the price of the heads. This change also bumped the compression, which is why this modification is worthy of consideration. Generally, a CNC chamber is also worth some combustion efficiency that is hard to measure unless we did some kind of back-to-back test on the same set of heads.

The Brodix oval-port head has a very strong intake-port flow curve and a decent exhaust-port curve considering its stock exhaust-port exit location.
The Brodix has a decent exhaust port, but because it is a stock exit-location port, the exhaust-flow numbers are not as strong as the TFS or Darts. This may explain why the Race-Rites benefited at the top a little more from the dual pattern cam. Our only complaint with these heads is that the valve-cover rail is low and spills oil on the headers when we remove the valve covers. Brodix chose to do this to make the heads easier to fit into tight engine compartments faced with clearance problems around A/C compressors and power brake boosters. Overall, this is a great oval-port cylinder head.

Brodix Race-Rite Oval Port2.25/1.88 valvesChamber 118 cc (110 cc CNC as tested)Intake-port volume: 270 ccStock exhaust-port locationIntake-port cross-section: 3.08 sq. in.PN 2061001 (RR BB-O)

Valve Intake Exhaust E/I
Lift (w/ pipe)
0.100 74 64 86%
0.200 163 113 69%
Note: This flow data was collected on an as-cast head without CNC chamber mods.

We set up the peanut-port heads with the same good Comp valvesprings, titanium retainers, and roller rocker arms. We also used a set of Comp 0.300-inch-thick spring seat inserts to take up the extra room created when we got rid of the stock exhaust-valve rotators.

GM Iron Peanut Port
This cast-iron head is called the peanut port because the intake ports are not much larger than their namesake. Omar Cabrillo at Coast Motor Supply in Canoga Park, California, helped us out by supplying a pair of the heads complete with tiny stock valves, new guides, and a basic valve job. These peanut ports are roughly 30 percent smaller than an aftermarket 270cc version. There are larger factory oval-port, cast-iron, open-chamber heads at 250 cc, but the only ones we could find had been modified, which would not be representative of an OE head. But don't count these peanut clusters out. If you were looking to build a budget-oriented Rat for towing where power above 4,500 rpm was not a concern, these heads would be an excellent choice with almost 600 lb-ft of torque at 3,200 rpm. If you were to pocket-port these heads and add larger 2.19/1.88-inch valves, you could make 530-plus horsepower. That's not bad for iron castings.

GM 236 Iron Peanut Oval Port2.06/1.72-inch valves120cc chamberIntake-port volume: 208 ccStock exhaust port locationIntake-port cross-section: 2.43

Valve Intake Exhaust E/I
Lift (w/pipe)
0. 100 56 44 78%
0.200 125 90 72%
The SetupThere are a boatload of variables involved in testing five different Rat motor heads. We quickly discovered that each of them demanded wildly different pushrod lengths based on changes in valve length. For example, both the TFS and Dart heads use 0.250-inch-longer intake valves that require a taller pushrod. Brodix adds 0.100 inch to both the intake and exhaust valves, while the Edelbrock valves are stock length. And don't forget, we skewed this whole deal with a hydraulic roller cam that uses a much taller lifter, which effectively shortens the pushrods. Mix in the fact that all Rat motors use different-length intake and exhaust pushrods and you've got a major science project just in pushrod lengths. After much gnashing of teeth, we ended up with six different pushrod lengths for our five subject heads. Just for fun, many of the heads also required lash caps on some of the valves to create sufficient clearance between the Comp steel Magnum 1.7:1 roller rockers and the valvespring retainers. Whew! The next time you hear a buddy complain about how much money custom engine builders ask for assembling an engine, smack them upside the head and tell them we put a solid 20 hours into setting up these heads so that they would perform (and survive) as intended.

But wait-there's more. We also realized that in order to generate a truly fair comparison, all the heads would require the same valvespring pressure. This would eliminate valve float as a variable, which was very important. One item we had no control over was that larger-diameter valves automatically weigh more than smaller valves. To accommodate all the different valve weights, we decided on a Comp Cams PN 933 spring with a common installed height of 1.950 inches. The 933 measured 175 pounds at 1.950-inch seat height with 440 pounds of open pressure at 0.550 inches of valve lift.

Finally, all but one of these heads required its own specific head bolt set as well. It took a big stack of ARP fasteners to get the job done, and we appreciate all the help that ARP gave us to make this test successful.

Pushrod Chart
Because these heads were fitted with several different valve lengths, this demanded multiple custom pushrod lengths. Comp's adjustable checking pushrods and broad Hi-Tech 31/48-inch pushrod selection made it easy to set up the proper rocker geometry with custom pushrod lengths in 0.050-inch steps. The following chart lists the pushrod lengths we established for our hydraulic roller-cammed 496, but you should still take the time to measure your own required lengths to ensure accuracy. The chart lists each Comp Hi-Tech pushrod length (in inches) with each part number in parentheses underneath. These Comp Hi-Tech pushrods can be ordered either individually or in sets of 16.

We used a Height Mic from Powerhouse Tools to establish a common installed height of 1.950 inches for all five sets of heads. That meant measuring a total of 80 valves and shimming each one within 0.010 inch to ensure each valve and spring combination produced similar loads.
Cylinder Head
Pushrod Iron Stock Brodix Dart Edelbrock TFS
Intake 7.75 7.60 7.85 7.50 7. 90
PN (8905) (8902) (7980) (8900) (7984)
Lightweight RetainersThe problem with big-block Chevys has always been big, heavy valves and valvetrain parts. That's why all aftermarket big-block Chevy heads come with 111/432-inch valve stems instead of the stock 31/48-inch stem. Since valvetrain weight is an issue, we elected to use the Comp 933 dual springs matched with a Comp 10-degree titanium retainer to reduce weight. The difference in weight between the normal-steel 1.550-inch-diameter retainer at 35 grams and the titanium at 18 grams is almost half at 17 grams. This may not sound like much, but it's huge. Just as we completed our testing, we learned about new lightweight tool steel retainers from Comp Cams that are only slightly heavier than titanium, yet as strong as steel and, best of all, roughly half the price! We've included the part number in our parts list. By reducing valvetrain weight, we don't have to run as much valvespring pressure, which makes life easier for the entire valvetrain. How often do you get an improvement in performance while also reducing cost? Technology is a wonderful thing.

Compression LessonsEach of the heads we tested had a slightly different combustion-chamber volume, which means static compression was another unfortunate variable in this test. The accompanying chart indicates the variation in compression. Both the Edelbrock and the Brodix (with its CNC machining) had the smallest chambers, so they benefited from the highest compression, while the Dart had the largest chamber and therefore the least compression. The difference is almost a full point of compression, and since one point is worth roughly 2 to 3 percent power, both the Edelbrock and Brodix probably received a decent horsepower bump. Had we milled the Dart heads to 110 cc, for example, that might have added another 10 hp, which would have made a significant difference throughout the entire power curve, perhaps pushing peak horsepower very close to 600. Yahoo!

Head Combustion Compression
Chamber (cc) Ratio
Stock Iron 120 9.7:1
We bolted in a set of coated Hedman 2-inch street headers in our '66 Chevelle chassis to see if the raised exhaust-port heads like the Dart and TFS would fit, which they did very nicely, thank you.

Test FitOne of the biggest headaches for big-block engines is packaging the exhaust. When we began this test, it appeared that the raised exhaust ports on the Dart and TFS heads might be a problem when it came to fitting chassis headers in a car, so we decided to put the heads to a simple test. We bolted a 454 iron-block in a '66 Chevelle along with the stock steering column and Energy Suspension motor mounts. We then bolted on the Edelbrock heads along with a set of Hedman 2-inch chassis headers. The Edelbrock heads fit with no clearance problems, so we then tried a TFS head with the same headers. One tube came very close to the steering column and probably would require a slight dimpling, but that was the only real consideration. We did not have the clutch linkage in place, but that did not appear to be an obstruction. Overall, we were pleasantly surprised that the raised exhaust-port heads still allow the headers to clear, which means we wouldn't have to do header surgery in order to make them fit.

Test Variables
As you've seen, three of the four heads in our test are very close in overall power. One variable that affects any test like this is cam timing. In this case, we chose a dual-pattern camshaft that offers 8 degrees more exhaust duration compared to the intake side. This probably helped the Brodix and Edelbrock heads that had less favorable exhaust flow numbers while perhaps hurting the Dart and TFS heads slightly. The Dart and TFS heads both have raised exhaust ports and strong exhaust flow numbers that likely would have responded with more power by using a single-pattern camshaft. We really can't say that with certainty unless we test this idea, but we have seen results like that with other engines offering high-flow exhaust ports. This is the problem with choosing one camshaft profile for testing multiple cylinder heads. It's entirely possible that the Dart and TFS heads would have produced much stronger peak torque and horsepower numbers had we chosen a single-pattern camshaft. Now you can see why the results of this kind of testing cannot be considered chiseled in stone unless a whole battery of cams go with it. This just gives you something more to think about.

Testing all these heads demanded serious planning since each head required its own specific set of Comp valvesprings and retainers, custom-length pushrods, and ARP head bolts.
Edelbrock Perf. RPM-O 60479 Summit Racing $1,779.00
Dart Pro-1 oval, assm. 19000112 Summit Racing 2,483. 90
Comp 10-degree locks 611-16 Summit Racing 22.88
Comp pushrods, 31/48 in. (see chart)** Summit Racing 16.99 ea.
Comp 111/432-in. lash caps 621-16 Summit Racing 35.75
Comp spring insert 4779-8 Summit Racing 33.99
This is the PN without the CNC chamber Brodix option CNC-chamber price $225.00

The TestOnce we had all the heads assembled and configured, we loaded up the Rat and all the heads and assorted accouterments in the back of our trusty GMC pickup and piled it all up in the dyno cell at Westech. Steve Brul put on his kidney belt, and we set to work thrashing on the Rat.

The procedure for the first test was to bring the engine up to temperature and then go through a series of jetting and timing tests to establish the baseline for the rest of the cylinder heads. It turned out that all the heads used 36 degrees of lead and the same jetting from the Barry Grant Mighty Demon carburetor, which made the thrash a little easier. Once we had a good tune-up, we made three full pulls on each combination from 3,200 to 6,200 rpm, then averaged those runs together to create a power curve for each engine.

Looking at the numbers, the iron heads performed better than we thought they would, while the aluminum heads were very close in terms of overall power. If you look at the overall torque curve of the four aluminum heads, all four are extremely close from 3,200 through roughly 4,800 rpm, where the Edelbrock heads begin to drop off slightly. That also shows up on the horsepower curve. While the power difference appears significant on the horsepower charts, please read the Simulated Dragstrip sidebar. We tested all five heads in a digital Chevelle down a virtual quarter-mile. What you'll discover is that this power discrepancy is not nearly as critical as it appears.

What's also interesting is that the intake flow curves on the TFS and Dart heads are almost identical, which transfers over to the horsepower and torque curves. Rather than get bogged down by too much detail about the power curves, it may be more important to point out how amazingly close all four heads were in terms of average power. With an average torque difference of only 8.7 lb-ft and an average horsepower difference of even less at 8.1 hp, there's a average spread difference of 1.5 percent. That's almost imperceptible in the car.

What all this means is that you really can't make a bad choice when it comes to any of these heads. Especially when you consider that there was a slight difference in compression. Had we evened up the static compression, it would certainly have helped the Dart and TFS heads the most, especially in terms of peak numbers, but it also means that the average differential would probably be a little wider, but still around 2 percent.

Also, since the cam was intentionally conservative, it's clear from the flow-bench data that all of these heads would respond with more power with another 0.030 to 0.050 inch of additional valve lift. That could come in the way of a switch to perhaps 1.8:1 roller rockers, because it gives us the lift without having to go to a longer duration that will only kill some of that brutal low-speed torque.

What's truly impressive is that this simple, oval-port, hydraulic roller-cammed 496 is capable of cranking out almost 630 lb-ft of torque at a very streetable 4,000 rpm with oval-port heads and a dual-plane intake manifold. We plan to bolt a single-plane intake on the Dart head package, and this will certainly push our 496 into the 600-plus horsepower zone. Either way, this is a killer power package disguised in conservative attire. So build a 496, paint the heads and dual-plane intake manifold orange, tell the world it's a mild 396, and blow their doors off. You just might get away with it-until the word gets out.

Iron Stock Edelbrock Dart TFS Brodix
3,200 595 363 610 372 605 368 612 373 619 377
4,400 581 487 609 510 606 508 616 516 616 516
4,500 577 495 607 520 604 518 614 526 613 525
4,600 572 501 605 530 603 528 613 537 611 535
4,700 565 506 602 539 602 539 610 546 609 545
5,200 525 519 576 570 583 577 590 584 588 582
5,300 515 520 570 575 578 583 583 589 583 588
5,400 507 521 563 579 572 588 576 593 576 593
5,500 496 519 555 581 566 593 568 595 569 596
Peaks and Averages
Avg. TQ Avg. HP Peak TQ Peak HP
Iron 541.1 475.0 595 521
Edelbrock 582.1 514.9 618 582

Price Vs. PerformanceHere's where this gets interesting. The Brodix, Dart, and TFS heads all made strong peak power, leaving the Edelbrock slightly behind. Then we divided the price of each pair of heads by their peak horsepower. Here, the Edelbrock is the clear winner in terms of horsepower per dollar. One note for clarity's sake: We added the price of the Brodix CNC chamber modification to the price of the heads, since that's the way the heads were tested. What this shows is that the Edelbrock heads offer excellent power for the money. There's something to be said for combining value with all-out power.

Heads Price (pair) Dollar/HP
Edelbrock $1,779.00 $3.05
TFS 2,095.95 3.52
Brodix 2,358. 90 3.95
Dart 2,483.90 4.17
Simulated DragStripHere's where we make dyno numbers relevant to the street. Testing each of these heads in the same car would have been fun, but there wasn't time, and they closed our favorite dragstrip. So we did the next best thing and loaded each of the five Rat head power curves into a simulated 3,700-pound street car with a TH400 trans, 3,000-rpm-stall speed converter, a 3.55:1 gear, and 28-inch-tall sticky tires 12 inches wide. Using the Quarter Pro dragstrip simulation program, we ensured that tire spin was eliminated so that we could evaluate each head based on its true potential.

We simulated a typical 80-degree day just above sea level, so these numbers are relatively quick. Even if a normal street car could hook up (which is questionable), these e.t. 's and speeds are probably a bit optimistic. Nevertheless, the differential between all the aluminum Rat heads is small-merely 0.08 second and 1 mph. Now factor the price again into this equation and you can see that the Edelbrock heads look really good. The Brodix, Dart, and TFS are so close that reaction time would determine the winner in that race. Also note that even those lame peanut-port heads pushed the test car into the very low 11s. This is bench racing at its finest.

Cylinder Head Quarter-Mile
Iron peanut port 11.05 @t 120.0
Edelbrock 10.69 @ 124.8
Dart 10.63 @ 125.6
TFS 10. 62 @ 125.8
Brodix 10.61 @ 125.8



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Here’s a summary of my 496 BBC to add to the thread. It has a pump gas friendly 10.35:1 comp. ratio, Edelbrock Performer RPM oval port heads with a mild port job, and a healthy Comp solid roller cam.

It was in my 71 Nova when I bought it and powers thru a manual TH400, 3000 stall converter, and a 9” rear end with 4:11 gears and a Detroit Locker. It's a real tire shredder with 629 HP and 622 ft-lbs of torque on tap (per the Desktop Dyno). She can easily smoke the tires at 50 MPH .

496 ci Big Block Chevy
GM 454 block, 4 bolt mains
Scat 4340 forged steel crank; 4.25” stroke (TMC-4-454-4250-6135)
Blue Cat H-beam forged 6.385” connecting rods (CAT-CRS-6385)
ARP main studs (#135-5601)
SRP pistons, 10.35:1 compression (TMC-142991); Sealed Power rings (SEA-R-990460)
Comp Cams XR286R-10 (#11-772-8) solid roller cam; 0.653”/0.660” lift; 286°/292° adv. dur.; 248°/254° dur. @ 0.050”; 110° LSA
Cloyes Hex-A-Just double roller timing set (#9-3110A) w/ billet steel sprockets
Edelbrock Performer RPM oval port aluminum cylinder heads (#60455), 110cc chamber, 290cc intake runner, 110cc exhaust runner, intake valve- 2.19”, exhaust valve - 1.88”, mild port job

Crane stud girdle (CRA-13602-1)
Crane 4130 Chrome moly steel pushrods, 3/8” dia., intake length: 8.250”, exhaust length: 9.250”
Comp Cams stainless steel 1.7:1 rocker arms
Fel-Pro #1027 composition type head gaskets, 4.370” bore, 0.039” compressed thickness
ARP head studs
Edelbrock 454-O Victor Jr. (#2904) aluminum oval port intake manifold, port matched to heads
950 CFM Quickfuel 4150 style carb
Milodon 7 qt. oil pan
Melling high volume oil pump (MEL-M-77HV)
Hooker Super Comp ceramic coated headers 2 1/8 ” primary tubes, 3 ½” collectors
MSD Digital 6 ignition system, MSD Blaster 2 coil, MSD distributor (MSD-85551)

Kenny Bee

71 Nova 496.jpg


This does look like a well built BBC if you check all the necessary clearances !

Have you been to the track to get some times?
I didn't build this engine. I bought the complete car (a 71 Chevy Nova) about 5 years ago with the 496 in it. I subsequently sold it to my son a while ago when I bought a 69 Nova roller drag car, but he has moved on to other interests, so I bought it back from him last year.
I haven't been to the track yet as I need to add a driveshaft loop and get the seat belts recertified.
spinning a 4.25" stroke bbc crank to 7000 rpm plus or even 7000 rpm frequently,
is generally not conducive to anything like long term durability
thus the mandatory need for rather expensive and far stronger than stock OEM parts in the rotating assembly and valve train,
and the need for improved cooling and lubrication system mods and upgrades


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