is it peak hp numbers or a good street combo your after?


Staff member
OK you've decided you can,t live without a killer 383 sbc,
you need to select the parts and you want to build an engine you can be proud of,
the first question is whats your budget look like,

quickly followed by what will you be using the engine for,
and do you have the drive train to match that engines power curve.
be sure you, measure EACH bore and EACH piston,
(CORRECTLY with the proper tools in the way the tool and piston manufacturers suggested)
and number them on an engine build sheet indicating the bore and piston diam.

from large to smallest on each and install them on each cylinder to get the most consistent piston to bore clearance's
yes the difference may only be a few ten thousands if the bores are machined correctly, but you'll get the best results , most consistent lubrication, best durability and less heat build up that might result in detonation issues that way. its the little things that add up to making a good durable engine assembly,
BTW check rod orientation, so the beveled sides don't fact the adjacent rods, and check the bearing clearances with plasti guage
every part you choose is a compromise , and may require changes,
that cost you in time, money or performance to some degree,
and almost every part will require a bit of fitting or clearance work,
or adjustment to fit and function to get the best results
if it drops out of the package and bolts together as it drops out of the package,
its almost certain its not functional to nearly its full potential

your job is to think things through carefully and make sure parts fit and function to their full potential,
little things like checking piston ring end gap, verifying bearing clearances, and ccing the heads and checking piston to valve clearance, degreeing in the cam and verifying the valve train geometry, polishing combustion chambers, getting a decent 3 angle valve job,verifying the piston to bore clearance, MATTER's

and theres that P.I.T.A. FACT that building an engine to produce impressive PEAK POWER,
you can brag about to your buddies almost always results in an engine with less than ideal street drive-ability,

especially if you want good gas mileage or like to cruise at 2000 rpm
every choice you make is a compromise in some area,
if you want massive low and mid rpm torque and instant re responsiveness, in your engine your very likely to be trading those characteristics at the expense of high peak horse power, if you want bragging rights and impressive power your very likely to pay a price in less than ideal manors in traffic and loss of low rpm power , theres EASILY A POTENTIAL OF 80-120 HORSEPOWER DIFFERENCE IN YOUR SELECTION OF HEADS CAM AND COMPRESSION RATIO ALONE
wider LSA smooths out the idle but it reduces overlap, the increased overlap tends to allow cylinder fill at a bit higher rpm and it also tends to kill off a bit of low rpm torque







The following tables illustrate how variations in lobe separation angle and cam
timing will effect the behavior of the engine in which the camshaft is installed.


Advancing.......................................... Retarding
Begins Intake Event Sooner................. Delays Intake Closing Event
Open Intake Valve Sooner ........................Keeps Intake Valve Open Later
Builds More Low-End Torque................. Builds More High-RPM Power
Decrease Piston-Intake Valve Clearance Increase Piston-Intake Valve Clearance
Increase Piston-Exhaust Valve Clearance Decrease Piston-Exhaust Valve Clearance

you would be foolish to ignore the available info, in these links

search.php?search_id=active_topics ... cation.htm ... ine_build/

if your building a sbc street/strip engine every component works a part of a total system, your always restricted by the weakest link in the chain, or the biggest restriction, and with engines its air flow rates, fuel/air ratios,cylinder scavenging,ignition advance curve and compression that determine a great deal of your potential power.
keep in mind you need to think thru the combo as a package where all parts selected must complement each other and be designed to operate in approximately the same basic rpm band and flow and effectively burn and use the pressure generated from similar amounts of fuel/air mix.

one very common mistake is selecting a cam duration,that exceeds or limits the engines rpm band, a rear gear ratio,thats not matched to the intended power band,or selecting a compression ratio or set of heads that can,t operate with the other components in the same power band efficiently
the best heads matched to a restrictive intake or the wrong cam will result in a DOG just as surely as a great intake and crappy heads with low compression, or any of a few dozen other miss-matched parts.
I think most of us have run into a great many similar choices, between buying tools and auto parts,
its simply the result of a limited budget ,in most cases,
and most of us make a few mistakes ,
but as long as you keep the goal of building the car in mind you'll do ok.
after you gain experience there's both engineering and art involved in the process,
you'll generally start with a goal, you've envisioned for your car, reality and physics will provide some of the limitations, you'll be limited to a budget and at times by your access too tools and limited by your skills and knowledge, youll generally start,by simply making a very detailed list of the components you want too use ,to upgrade and modify the car to gain the performance and look of the car, and once you have that list of components, and being forced by going back through that detailed, list and doing the required math too verify you have selected the correct matching parts, and when you find you have to change a few components you go back, change the list and again revue the math, most of us start out without the required knowledge to accurately match parts and your goal.
yet this process forces you to do some research into what you can reasonably accomplish with the tools and skills you have and the realization that you may need to acquire both skills and more tools as you proceed. as you read through most of the builds listed and discussed on this web site,
youll eventually see a strong trend, towards what I and many other knowledgeable engine builders have been forced over time into recognizing.
the trend is simply that only engines built for max long term durability and max torque in the useful rpm range are making any financial sense.
as Ive stated many times, you have to finish a race to win it! and your never going to build a client base ,
if the engines you build make killer power on a dyno but need rebuilding in a couple months time.
theres several threads on builds here on this web site, and a great deal of time and research is devoted to extended durability, cooling and lubrication ,
and carefully selecting components, and machine work done, designed for max strength, for the dollars spent!
I used to ask guys
"would you prefer to build an engine that if you keep it well tuned and change the oil regularly,
will most likely still be running in 10-12 years, without changing major components, or
would you rather have an additional 25-30 hp,and need a rebuild every 3-6 years,
but have a much better chance it won,t last half that time span....
especially in a muscle car driven on the street,
where either engine choice will destroy street tires effortlessly,
and get you a ticket effortlessly for speeding any time you get stupid?"


Change Cam - Gain 78 HP ..... "article on page 22, in the magazine" [Best of Tech /Winter 2003]

A few years ago there were claims by a magazine of adding 78 horsepower to a wimpy 8.6:1 compression-ed 355 sbc equipped w/"the usual hot rodding parts" headers, 750 Speed Demon carb, Edelbrock Performer RPM Air-Gap intake, 2.02/1.60 Summit aluminum heads, MSD, ect.

Just using an Erson TQ40 cam kit [218/228@.050 duration][.472 valve lift, w/1.5:1 rockers]
instead of the stock small block Chevy [195/202 duration] factory type [.390/.410 lift] camshaft ...

Using this Erson TQ40 cam, it showed gaining a maximum of 78 hp @ 5,600 RPM = [403 hp/maximum] .....
and gaining 20 pounds of torque, @ 4,400 RPM = [418# torque/maximum] over the stock low lift camshaft.

Oddly enough, from 2,000-to-3,900 RPM, results were [-1 horsepower] and [-4 pounds of torque].

Average gains from 2,000-to-5,900 RPM, were 44 horsepower & 35 pounds of torque .....

This Erson TQ40 cam showed gaining 78 hp & 78 pounds of torque, from about 4,000-to-5,900 RPM.

now 78 hp gain looks impressive but if you retained the stock rear gear and converter youll spend very little time in the 4000rpm-6000rpm power band so a cam like that won,t produce nearly the gains, in performance you might expect without making the matching drive train mods so the engine operates mostly in the new higher average power band, it makes little difference if your engine makes 100 more hp if it makes it only in an rpm band you seldom reach or use!.

if you want the car to run decent you need to significantly increase the air flow rates,and feed the required fuel to maintain the correct f/a ratio and that requires much better flowing heads,much better flowing intake and a cam with more lift and duration and a higher stall speed converter and a 3.54:1-or- 3.73:1 rear gear ratio
a cam that will move the intended power range high enough to make that intended power curve is required , but planing where in the rpm range that power curve is strongest is your first decision,..... all the components selected must match,that intended power curve, and the cam, compression ratio and head flow need to match that combos goal, you can build a good street combo with massive torque in the rpm range you normally drive, (usually 1800rpm-4500rpm, on most street cars) for use on the street or you can build a race engine with far better peak power (up in the (4500rpm-6500rpm range) but it won,t be nearly as much fun to drive at low rpms or on the street, in fact its only going to work great on a dyno or where you can drive while keeping the engine rpms in the 4500-6500 range in most cases
keep in mind if your gearing keeps the engine rpms in the 1500rpm-5500rpm range and the transmission shifts at 5500rpm under wide open throttle like most nearly stock engines do its rather useless to cam the engine or use heads designed to maximize power in the 5500-700rpm range
put your info into this program, don,t exaggerate or lie, just input what you really have top work with

a typical sbc makes about 1.1 ft lb of torque per cubic inch of displacement

your torque curve depends mostly on your engines displacement,compression,head, & intake flow and cam timing

the formula for hp is torque times rpm divided by 5252=hp
a higher torque peak generally increases power

this is a very typical dyno chart from an engine with stock heads a mild cam and stock exhaust and intake, as all components are designed for max low and mid rpm torque, you can easily move the peak hp and torque number higher , with larger head ports cam duration, better intake and less restrictive headers and exhaust but doing so tends to reduce the off idle responsiveness and torque, as every choice is a compromise in some area.
400 ft lbs at 3500rpm=267hp
400 ft lbs at 5500rpm=419hp
400 ft lbs at 6500rpm=495hp

you'll want to run about 10:1 cpr on the street to maximize performance, because on pump gas thats about the max you can use, but the cam selected effects the dynamic compression ratio so you can use a bit more compression with a longer duration cam and a bit less with a lower duration,
heads that flow about 250cfm or more at .500 lift are going to be a huge asset, but the port cross sectional area will tend to vary based on where you want peak hp,
if your going for an aggressive combo a bit more on the race end of the scale but a compromise to keep it semi-street-able, you'll usually need a 3.54:1-3.73:1 rear gear and a manual transmission or a 2700rpm-3000rpm stall converter to maximize acceleration, with a cam that's designed to maximize power in the 3000rpm-6300rpm band

personally if I was building as hot street combo, Id select a complete rotating assembly with matched components,from a single supplier, it will tend to avoid problems or finger pointing if parts don,t match and fit, specifically say you want those components and balanced, a good scat cast STEEL 9000 balanced crank and 5.7" connecting rods with 7/16" rod bolts,and forged pistons, do the research and make sure you get match and balanced parts
If it was a street and race combo ID also specify INTERNAL BALANCE and 4340 forged rotating parts



notice its right where the roller cams lobe design maximized the extra air flow potential that is the most effective flow area during the whole valve flow curve
and yes it frequently helps to match a roller cam to roller rockers as the reduced friction further helps the engines durability and ability to easily cope with faster valve train component acceleration, that tends to reduce heat and wear.
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches, thus it makes a great deal of sense to push the valve lift a bit over .500, and have an intake port that is at least 3.2 square inches in cross sectional area, if you want to maximize flow on a 2.02" intake valve



this is exceptionally useful for newer guys
the fact that peak lift is not where you gain the vast majority of the ports airflow potential
think about the math a bit , at 6000 rpm, the valve is going from seat to full lift and back to its seat,3000 times a minute, thats 50 time's a second
but that 50 times a second includes the full 360 degree rotation, peak lift rarely lasts more than 40 degrees of that rotation, or about 1/10th of that how much air flow can occur in 1 /500th of a second the valves are near peak lift


(if your stuck using restrictive heads, follow this build and use much of what can be used as its designed to maximize restrictive heads)

keep in mind you have a great deal of options,in parts that can be used,and your selection will have a huge effect on where in the rpm range you make the best power, and making 1.1-up to-1.4 horsepower per cubic inch is not that difficult, with the correct parts.
if you read thru the links and sub links youll find many tips and combos ... ock_build/ ... 5/A-P1.htm ... 1/A-P1.htm ... A16-P1.htm ... index.html ... A27-P1.htm ... calculator






here posted below are two 383s on dyno software with different heads cams and intakes almost everything else is similar,
look at the differences in torque and peak hp that the changes made in
BOTH the low range (1500rpm-4500rpm) (noticeably more low rpm torque)
and the upper or peak hp, (4500rpm-6500rpm) (a good deal more peak hp)




heres a chart I found that I don,t fully agree with, I think its a bit conservative, by about 3%-5% on the required cam duration ,required to avoid detonation with todays crappy octane fuel, but it at least gives you a base to work from, but Id suggest selecting a bit more duration
why not call crane,
lunati 1-662-892-1500
isky 323.770.0930
and talk to the tec support guys about what they suggest but DON,T mention anything any other cam manufacturer suggests during the conversations, just present the info on the parts used in that combo, rear gear ratio, compression, etc and see what they suggest, then make up your mind.


190cc heads tpi, mild cam (crane 119561)


Volumetric Efficiency: Is calculated by dividing the mass of air inducted into the cylinder between IVO and IVC divided by the mass of air that would fill the cylinder at atmospheric pressure (with the piston at BDC). Typical values range from 0.6 to 1.2, or 60% to 120%. Peak torque always occurs at the engine speed that produced the highest volumetric efficiency.
keep in mind as rpms increase so do port speeds and volumetric efficiency UP TO A POINT, WHERE THE TIME LIMITATION TO FILL AND SCAVENGE the cylinder limits power

210cc heads single plane intake wilder cam (CRANE 119601)

if your building a 383 sbc these links and sub links will help

SAFE piston speeds are best restricted to 4000fpm for stock components and 4500fpm for the better common aftermarket components
if your serious about building a performance engine you might want to consider a BBC over a SBC
you can generally expect to get between 1.0 to 1.3 ft lbs per cubic inch of displacement and 1.0 to 1.3 horsepower per cubic inch of displacement on your average street/strip daily driver SBC or BBC engine build
how the big block and small block engines differ. The answer is not only in displacement. A small block Chevy motor can be stroked and bored to over 400 ci . it comes down to bore centers. and much stronger OEM blocks and generally better flowing heads, The small block has bore centers spaced 4.4 inches apart. On the big block, those centers are at 4.84 inches.
as a general rule you can build a 396-402 BBC that can outperform a 400 SBC, you'll have a difficult time finding SBC heads that flow more than 310 cfm at a decent price, but many BBC heads flow in excess of 350 cfm, especially if mildly ported and aftermarket BBC heads that flow over 400 cfm are available

keep in mind your basic BBC With more metal separating the bores, there's extra space for cooling galleries and added potential for boring-out. Further, more metal means a stronger block. cranks and rods and the basic BBC block are significantly stronger than the average OEM sbc parts, If you're looking for big horsepower from your muscle car motor, a big block might be the way to go.
read these threads ... _heads.asp

IF your building a stroker big block,combo,you might find info here in the thread below and its sub links useful
keep in mind the 383 small block has become almost the standard its basically the 350 with a 1/4" stroker crank and a slight .030 over bore,to clean up and wear in the 350s bore
in the similar manor a 454 big block with a .030--.060 over bore and a 1/4" stroker crank assembly is used to build a 489-496 big block version
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while its fairly rare, some guys obviously do UNDER CAM engines , or select cylinder heads and intakes that restrict the max potential hp or mix an match components so that one part is potentially running at its max power range before a different component is anywhere near to reaching its full potential in the rpm range.obviously if you use a small combustion chamber cylinder head you may need a dished piston to get the compression ratio to the level you want.
youll need to sit down and calculate the complete combination of components , not randomly select parts, thats one of the most common mistakes , guys get deals on parts and fail to do the research to see if those parts will work on their application

if you select a cam with significantly more duration and lift than stock, the rear gear ratio, converter stall speed and compression must change to match, and the heads, intake etc, will also need to change or they become a restriction as the stock parts are designed to operate in about the 1200rpm-4500rpm power band, with exhaust emission and mileage as the main goals not peak hp


this first power graph looks almost pitiful until you realize its easily making far more than 100ftlbs and 100hp more than stock parts, and its almost all instantly available, and the stock transmission shifts at a lower rpm than the second graph power curve can fully utilize, making much of the potential hp useless...if your transmission shifts at 5500rpm, and you cruise at under 2300rpm with stock gears, the power the engine potentially might make at 6500rpm, that it never reaches is worthless

cylinder heads are expensive and it makes very little sense to buy really nice aftermarket heads that flow 290cfm at .700 lift and then use them on an engine with a TPI intake that flows 220cfm, and with a cam thats got only .420 lift, yet I occasionally see guys assemble car engines like that. or guys that install the large heads and a killer induction system on an engine with stock exhaust components and a mild cam with a stock stall speed converter.
the main problem I see in most cars with miss matched components is the result of guys wanting to save money reusing older components they currently own, while constantly upgrading other components to work at a higher rpm range that the few current parts can efficiently function at, or guys that get killer (DEALS) on parts that don,t fit their combo...few of us can resist a screaming bargain, but that $1200 tunnel ram and carbs you see at the swap meet for $500, while a good deal, you can, absolutely bet its not going to work to its full potential on a car with stock heads and a mild cam and a 3.07 rear gear.
yes its far more common for guys to install a radical cam, into a car engine with what is essentially mostly stock drive train gearing and heads etc. but miss matched components will not function correctly in either case!
If your goal is a street strip car, youll need to make changes to increase power, but every change is a compromise in some area, if you select a roller cam designed to maximize the power potential of a 383 that runs on 93 octane, high test pump gas,as an example your effectively looking to match a power band in approximately the 4000rpm-6700rpm power band, and its going to require heads that flow about 270cfm and a .600 plus lift cam with about a 250 duration @ .050 lift or more and about a 10.5:1plus cpr, those components will require matching the rear gear and stall converter to that same rpm band, and its not going to be ideal in traffic on a street car, so obviously if the cars used as daily transportation youll cut back , or compromise on the component rpm band to match the application you do need to operate in.
each of us has a tolerance for noise, and how easy the engine runs in traffic, and most of us can,t live without power brakes, air conditioning or if you can,t hear conversations in the car

heres my cars combo, its not nearly ideal on long trips but thats ok because its a weekend TOY, not daily transportation I built that combo specifically to run a nitrous kit and still be about as radical as I could tolerate before I use nitrous, but its its performance on nitrous not its N/A manors that took first priority


in an ideal RACE combo your power curve would look similar to this and youll have a converter stall speed and rear gear ratio and tire diam. that allows the engine to stay in (in this case the 4000-6500rpm power band) but thats hardly ideal in a street car engine combo

reading the links posted and sub-links will lead you to charts , graphs etc,
that point you to the answers and discussions about how and why certain components work and how parts are matched to be more effective




TIGHTER 104-110 LSA tend to increase scavenging efficincy but at the cost of less smooth idle

LSA lobe separation angle is locked into the cam when its ground and can not change, if its ground at 110,degrees or 114 degrees it will stay that figure

LCA lobe center angle, can be changed
if you advance the cam 4 degrees both the intake and exhaust lobe opening and closing points open and close 4 degrees earlier.
if you RETARD the cam 4 degrees both the intake and exhaust lobe opening and closing points open and close 4 degrees later.

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.






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lets assume youve got a good set of ported corvette aluminum heads or vortec heads ,and a 383 sbc youve built that has 10:1 compression ratio, youve got a 750cfm vacuum secondary carb and headers on your car, with a stock exhaust, and you want to use as much of the stock parts that you have as you can to lower the max cost of the engine build, and your on a rather restricted budget, you find a sale on cams and intakes and your choice is between a good dual plane intake or a good single plane, and between a comp 275 h-280h cam or a comp 292h cam,you know your running a stock rear gear in the 3.07-3.36:1 range in a car thats rarely if ever going to the track and your going to need the car for daily transportation,
put your info into this program
why is it so difficult to understand that of the components you've listed, the best choice that will work, yet cost the least to upgrade, is a 275h-280h cam and that cam and heads, exhaust etc is the best with those heads(which are rather expensive to replace)matched to a dual plane intake which is a far better match to the 275h- 280h cam and your current heads than the single plane intake and the comp 292h cam your buddy insists is the cam that will make the most peak hp..?
I don,t know about your area, but used dual plane SBC intakes, at yard sales, craigs list, ebay etc. RARELY cost more than $100-$125.. usually less making the acquisition relatively painless.
use of a larger cam or the single plane intake will tend to move the power band higher than the head flow can effectively match effectively hurting the low rpm torque without much compensating gains in peak power due to the head flow restriction, your far better off maximizing the mid rpm power curve, in a street cars engine so you maximize the power in the rpm band you actually use on the street.
it seems to me a no-brainer that you want to spend the least cash for the maximum results and use as much of the current inventory of parts as you can to minimize cost and time.
your unlikely to spend even 5% of your time spinning the engine over about 5800rpm so concentrating on maximum power in the 1500rpm-5800rpm band makes more sense than trying to get a bit more peak hp at lets say 6000rpm

a cam like this might be great in a daily driver 383 built with 10:1 compression and 3:73:1-to-4.11:1 rear gears, using a stock stall converter,as it will provide good low and mid rpm torque and if the heads flow well still make some power up near 6000rpm, but it certainly won,t maximize peak power levels, and surely reached peak torque well below 5000rpm, in a 383-to-406 sbc

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.

But be aware, Your cars displacement, compression ratio and drive train gearing will EFFECT YOUR RESULTS A CAM THAT MIGHT WORK RATHER WELL IN A 383-406 IS NOT NECESSARILY GOING TO WORK NEARLY THE SAME IN A in a 327, OR 350 DISPLACEMENT ENGINE,that cam that might be the hot ticket in a daily driver combo, 383-406, will be about the max duration that a car with a stock converter will tolerate and still function semi normally,in a 327-350, now if you have at least 3.45:1 rear gears it should not be a problem, but it would potentially be a P.I.T.A.,in SOME applications, idling a bit too high and jumping into gears etc. if the car was fairly heavy,has a stock stall speed,converter and lets say 3.08 rear gears.
swapping to a 2800rpm-3000rpm stall converter will allow you to run a noticeably larger cam
what Id strongly suggest is that you call a MINIMUM of 5-7 cam manufacturers and ask for advice on selecting a cam, once you know your cars compression ratio, stall speed, rear gear ratio, tire height, etc. then make a decision after averaging the suggested lift, duration, and LSA they suggest
calculate horse power from intake port flow rates[/quote]

every choice is a compromise in some area,
this may help, in my 383 with a full length 3" exhaust and a nitrous system,

this was a great street driving and cruising cam, killer low and mid rpm power but it started to peak at about 5500rpm in my 383 and I wanted a bit more so I swapped to the 00471 then to the crane 119661

the crower 00467 was an excellent street strip & transportation cam choice for daily transportation while the larger cams even the 119661 I settled on were marginal for daily transportation

my current crane 119661 hydraulic roller cam above works great with a 3.73 rear gear and 3000 stall


I used this crower cam for several months which made noticeably better peak hp but was a P.I.T.A. to drive in traffic, its obviously some what of a judgement call on what your willing to put up with, and obviously if your combo of parts differs you'll get different results, but on longer drives I don,t think the 00471 is ideal, but for a week end toy its fine.
you want to keep in mind that making excellent peak hp up at 6300rpm where you rarely reach it for bragging rights, is not all that useful in a street car,compared to having instant torque in the 2500rpm-4500rpm band where you spend 99% of your time while driving on the street

also remember theres a balance or trade-off in components youll select the larger the engines displacement, and the higher the intended rpm range, the larger the cylinder head intake port cross sectional area must be to effectively flow the required air/fuel mix. and the more restrictive the heads intake ports are in relation to the displacement the longer duration and the tighter the cams LSA , usually needs to be at any given power range.
thats one reason the better aftermarket heads can make better power with a milder cam, if the heads flow better the valve doesn,t need to be held open as long to flow the required air/fuel mix.

related info



viewtopic.php?f=50&t=1249 ... ewall.html ... calculator



this chart showing the new WIEAND AIRSTRIKE intake flows better than the comparable edelbrock vortec intake might prove to interest some guys

good flowing heads that flow at least 250cfm at .500 lift, with 200cc-215cc ports, a good low restriction intake, (wieand or edelbrock) 10:1-10.5:1 compression and a cam in the 230-245 duration range, and 3.45:1-4.11:1 rear gears and a manual transmission or 3000rpm stall converter, makes for a responsive combo on a 406 sbc

keep in mind theres three basic factors that are interlinked in that each has some effect on how the other two will effect the engines power curve

duration controls the number of degrees of rotation the valve takes from the time it lifts off its seat until it re-seats, the is the TIME the valve will be open and effects the rpm range , the cam will most efficiently operate in.
LIFT, controls the distance the valve opens,and combined with the valve diameter limits the valve curtain, so combined with duration in controls potential flow.
your engine displacement, compression ratrio, potential head flow and header scavengine also will effect the power curve\


LOBE SEPARATION ANGLE will effect how effectively the exhaust can scavenge the cylinders and low rpm reversion pulse strength to some degree thus idle quality, as the period of time while both valves are open at the same time, greatly increases cylinder scavenging.








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lets assume you can,t sleep untill uyou build a killer 406 SBC with 500 plus hp,
read thru this links
please post lots of clear , detailed pictures of your progress,, take your time and get the clearances correct and use lots of assembly lube or you may regret rushing thru the process later

READING THRU these links should help









Id look over the 210cc AFR
profiler 210cc heads and Id build a 383-406 displacement with about a 10.5:1 cpr
yes you could get similar results from properly prepared 195cc heads but they would be slightly restrictive, the 210cc will be a better match PROVIDED you build a hot 383-407, naturally larger displacement has advantages

this intake
a decent 750cfm-800cfm Holley carb
rocker stud girdle
tall valve covers
A NAME BRAND 7-8 quart baffled oil pan and windage screen
a FORGED ROTATING ASSEMBLY with 7/16" 4340 connecting RODS
forged pistons matching the cylinder heads
low restriction exhaust with (X) pipe and decent full length headers
a DART BLOCK would be a huge improvement over a stock block here!

Id suggest a hydraulic roller cam similar to these, and a 3.73:1 rear gear, it won,t be really street friendly, as your power won,t start coming on really strong till about 3600rpm but it will have the 500 plus hp is built correctly.
KEEP IN MIND that a good deal of the power in any engine combo will be the result of how efficiently you blend factors like,
CYLINDER HEAD FLOW rates vs displacement
EXHAUST scavenging efficiency.(cam timing)
theres a good deal of math involved, that can be used to accurately predict the results but there's also an ART and SKILL to tuning and engine assembly, and experience goes a long way there.
and yes a slight mis-match of components, not getting the clearances correct, or a few degrees of cam duration,plus or minus from what the engine needs, and a few cfm difference in intake or exhaust restriction,flow, a few extra fractions of an inch of valve lift, a better or worse multi angle valve job and your up or down 60-80 hp...

heres the wild guess the dyno software says is likely from a similar combo

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Just got back from a dyno session on a '72 'vette...406, AFR 210's, Comp cams HR 242/248/110*. It put down 443 rwhp @ 6k , 445 rwtq @ 4,500. Dunno what that would be in flywheel #'s, but probably 550/550. Over 400 ft/lbs at the wheels from 2,700 thru 5,800. Not bad!
both builds are obviously similar and right in the same ball park, power wise, as you can reasonably assume a 18% loss between flywheel to rear wheel numbers

443 rwhp @ 6k , 445 rwtq @ 4,500 would indicate close to 540flwhp and 538 flwtq

Im always amazed at the guys that ask for advice and when you post a known combo of well proven components ,the first thing they want to do is look for ways to use much inferior components that cost less and then after building their only vaguely similar version, are shocked too find its not performing to their expectations.

now don,t get me wrong I fully understand being broke and very tight on funds, and I fully understand the frustration of having to wait while you acquire the funds and how theres always some tendency to get deals on inferior parts or have family emergency's drain your funds,

but I also know from experience, its far better to wait until you buy the correct parts have the correct parts than it is too rush to the assembly stage with inferior components just so you find you have a running engine.....but also find its far short of your intended power levels, and build an engine your never going to be happy with.
but doing something like reading thru a well tested combo then substituting stock vortec heads and a flat tappet hydraulic cam, because you already own those parts for the much more expensive aftermarket components like AFR 210cc heads and a crane solid roller cam, makes about as much sense
as reading a recipe for chocolate cake that calls for 2 cups of white sugar , and substituting two cups of salt, because it looks very similar, and you already have it on hand, and being shocked when you find the resulting cake doesn,t seem to be nearly as good once baked and frosted

and YES Ive fallen into the same trap and made the same mistake in the past, and watched countless others make that mistake ,but I learn from my screw-ups some guys never seem to!, IF YOUR BUILDING A CRUISING ENGINE, THAT WILL NEVER SEE 5000RPM, IT WILL REQUIRE FAR DIFFERENT COMPONENTS FROM A RACING COMBO< SO DO THE RESEARCH ON HOW AND WHY CERTAIN PARTS ARE USED AND HOW TO MATCH PARTS IN AN APPLICATION

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


Look thru the combos in the links and notice that as long as the components selected remain fairly well matched, the higher the head flow rates and the larger the displacement and the higher the compression ratio, and with a matching cam timing, the better the power curve ,that results ... -23-degree ... view&id=48 ... 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











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basically it just points out that making more torque at higher rpms tends to allow you to have the option to gear the car differently so you can more effectively use the torque, and actually use the power produced. most chevy ,V8 engines will produce 1-1.2 foot lbs of torque per cubic inch of displacement,the rpm band where you produce that power in the engines rpm range is in large part determined by the compression ratio, cam timing, and potential cylinder head and intake port flow rates and the exhaust flow restrictions and scavenging



one very common mistake is selecting a cam duration, rear gear ratio, compression ratio or set of heads that can,t operate with the other components in the same power band efficiently
the best heads matched to a restrictive intake or the wrong cam will result in a DOG just as surely as a great intake and crappy heads with low compression, or any of a few dozen other miss-matched parts.
if you want impressive bragging level hp you need to design a combo capable of operating efficiently above 5800-6000rpm but thats NOT necessarily going to be a good street engine

horsepower =torque times rpm divided by 5252
so 370ft lbs at 3700rpm=261hp
but 370ft lbs at 5700rpm=401hp
and the heads , rear gear ratio,and cam that operate effectively at 3700rpm wont be the same as those matched to 5700rpm, you might also keep in mind youll make approximately 1.1-1.2 hp per cubic inch of displacement and piston speeds below 4200fpm are strongly recommended for long term durability, and hydraulic lifter valve trains seldom do well over 6300rpm, and about 10.2:1 static compression is about the max crappy pump gas will tolerate IF MATCHED TO THE CORRECT COMBO
Horsepower and Torque - a Primer

There's been a certain amount of discussion, in this and other files, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift. This is meant to be a primer on the subject.

OK. Here's the deal, in moderately plain English.

Force, Work and Time

If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done. Work requires movement. If you unbolt the weight, and apply a force sufficient to lift the weight one foot, then one foot-pound of work will have been done. If that event takes a minute to accomplish, then you will be doing work at the rate of one foot-pound per minute. If it takes one second to accomplish the task, then work will be done at the rate of 60 pound feet per minute, and so on.

In order to apply these measurements to automobiles and their performance (whether you're speaking of torque, horsepower, Newton meters, watts, or any other terms), you need to address the three variables of force, work and time.

A while back, a gentleman by the name of Watt (the same gent who did all that neat stuff with steam engines) made some observations, and concluded that the average horse of the time could work at a rate that would lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 pound feet per second, or 33,000 pound feet per minute. He then published those observations, and stated that 33,000 pound feet per minute of work was equivalent to the power of one horse, or, one horsepower.

Everybody else said okay.

For purposes of this discussion, we need to measure units of force from rotating objects such as crankshafts, so we'll use terms that define a twisting force, such as torque. A foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.

In fact, what standard engine dynamometers actually measure is torque (not horsepower) by using a resistance to hold the engine at a constant speed while at full throttle, and then measuring the resistance required to keep the engine from accelerating. Then we can calculate actual horsepower by converting the twisting force of torque into the work units of horsepower.

Here’s how:

Visualize that one pound weight we mentioned, one foot from the fulcrum on its weightless bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (Pi * a two foot circle), and, incidentally, we have done 6.2832 pound feet of work.

Okay. Remember Watt? He said that 33,000 pound feet of work per minute was equivalent to one horsepower. If we divide the 6.2832 pound feet of work we've done per revolution of that weight into 33,000 pound feet, we come up with the fact that one foot pound of torque at 5252 rpm is equal to 33,000 pound feet per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 pound feet per minute), and so on. Therefore, the following formula applies for calculating horsepower from a torque measurement:

Torque * RPM
---------------- = Horsepower

This is not a debatable item. It's the way it's done. Period.

The Case for Torque

Now, what does all this mean in car land?

First of all, from a driver's perspective, torque rules, to use the vernacular. Any given car, in any given gear, will accelerate at a rate that exactly matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 pound feet of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower tends to not be particularly meaningful from a driver's “belt in the back” perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching push back into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.

You don't believe all this?

Fine. Take your non-turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice how the seat belted you in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Okay. Now that we're all on the same wavelength (and I hope you didn't get a ticket or anything), we can go on.

Torque is What You Feel, but Horsepower Rules

So if torque is so all-fired important (and feels so good), why do we care about horsepower? Because (to quote a friend), "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing."

For an extreme example of this, I'll leave car land for a moment, and describe a waterwheel I got to watch a while ago. This was a pretty massive wheel (built a couple of hundred years ago), rotating lazily on a shaft that was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) pound feet of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm of its drive wheels in a flash, and the waterwheel would hardly notice.

On the other hand, twelve rpm of the drive wheels is around one mile per hour for the average car, and, in order to go faster, we'd need to gear it up. If you remember your junior high school science classes and the topic of simple machines, you'll remember that to gear something up or down gives you linear increases in speed with linear decreases in force, or vice versa. To get to 60 miles per hour would require gearing the output from the wheel up by 60 times, enough so that it would be effectively making a little over 43 pound feet of torque at the output (one sixtieth of the wheel's direct torque). This is not only a relatively small amount; it's less than what the average car needs in order to actually get to 60. Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us:

6 horsepower.

OOPS. Now we see the rest of the story. While it's clearly true that the water wheel can exert a bunch of force, its power (ability to do work over time) is severely limited.

At the Drag Strip

Now back to car land, and some examples of how horsepower makes a major difference in how fast a car can accelerate, in spite of what torque on your backside tells you.

A very good example would be to compare the LT-1 Corvette (built from 1992 through 1996) with the last of the L98 Vettes, built in 1991. Figures as follows:

Engine--------------Peak HP @ RPM-------------Peak Torque @ RPM
L98---------------------250 @ 4000----------------------340 @ 3200
LT-1--------------------300 @ 5000----------------------340 @ 3600

The cars are essentially identical (drive trains, tires, etc.) except for the engine change, so it's an excellent comparison.

From a driver's perspective, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to feel about as fast as the other to the driver, but the LT-1 will actually be significantly faster than the L98, even though it won't pull any harder. If we mess about with the formula, we can begin to discover exactly why the LT-1 is faster. Here's another slice at that torque and horsepower calculation:

Horsepower * 5252
------------------- = Torque

Plugging some numbers in, we can see that the L98 is making 328 pound feet of torque at its power peak (250 hp @ 4000). We can also infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point. On the other hand, the LT-1 is fairly happy making 315 pound feet at 5000 rpm (300 hp times 5252, over 5000), and is happy right up to its mid 5s red line.

So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occurring a little earlier in the rev range, but that is debatable, since the LT-1 has a wider, flatter curve (again pretty much by definition, looking at the figures). From somewhere in the mid-range and up, however, the LT-1 would begin to pull away. Where the L98 has to shift to second (and give up some torque multiplication for speed, a la the waterwheel), the LT-1 still has around another 1000 rpm to go in first, and thus begins to widen its lead, more and more as the speeds climb. As long as the revs are high, the LT-1, by definition, has an advantage. As a practical matter, a typical L98 6-speed car might cover a quarter mile with an ET of around 14 seconds at around 99 or 100 mph, while the equivalent LT-1 will generally be at least a half second faster, at 104 – 105 mph. Mind you, as I’ve mentioned, the LT1 doesn’t pull any harder – just longer.

There are numerous examples of this phenomenon. The Acura RSX Type S, for instance, is faster than the garden variety RSX, not because it pulls particularly harder (it doesn't), but because it too pulls longer in each gear. It doesn't feel particularly faster, but it is.

A final example of this requires your imagination. Figure that we can tweak an LT-1 engine so that it still makes peak torque of 340 pound feet at 3600 rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we extend the torque curve so much that it doesn't fall off to 315 pound feet until 15000 rpm. Okay, so we'd need to have virtually all the moving parts made out of unobtanium, and some sort of turbo charging on demand that would make enough high-rpm boost to keep the curve from falling, but hey, bear with me.

If you raced a stock LT-1 with this car, they would launch together, but, somewhere around the 60-foot point, the stocker would begin to fade, and would have to grab second gear shortly thereafter. Not long after that, you'd see in your mirror that the stocker has grabbed third, and not too long after that, it would get fourth, but you wouldn't be able to see that due to the distance between you as you crossed the line, still in first gear, and pulling like crazy.

I've got a computer simulation that models an LT-1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a bit conservative) to what a stock LT-1 can do at 100% air density at a high traction drag strip, being power shifted. However, our modified car, while belting the driver in the back no harder than the stocker (at peak torque) does an 11.96, at 135.1 mph - all in first gear, naturally. It doesn't pull any harder, but it sure as heck pulls longer. It's also making 900 hp, at 15,000 rpm.

Of course, looking at top speeds, it's a simpler story...

At the Bonneville Salt Flats

Looking at top speed, horsepower wins again, in the sense that making more torque at high rpm means you can use a stiffer gear for any given car speed, and have more effective torque (and thus more thrust) at the drive wheels.

In fact, operating at the power peak means you are accelerating the absolute best you can at any given car speed, measuring torque at the drive wheels. I know I said that acceleration follows the torque curve in any given gear, but at any given car speed, horsepower is the absolute governor of how fast you can accelerate. This means that at any given instant, it's power that determines how fast you can accelerate, and not torque. In fact, horsepower is a kind of shorthand in this context. No matter what gear you’re in or what the final drive ratio is, more power at that speed means more acceleration because you’ll have more torque at the drive wheels. I'll use a BMW example to illustrate this:

At the 4250 rpm torque peak, a 3-liter E36 M3 is doing about 57 mph in third gear, and, as mentioned previously, it will pull the hardest in that gear at that speed when you floor it, discounting wind and rolling resistance. In point of fact (and ignoring both drive train power losses and rotational inertia), the rear wheels are getting 1177 pound feet of torque thrown at them at 57 mph (225 pound feet, times the third gear ratio of 1.66:1, times the final drive ratio of 3.15:1), so the car will bang you back very nicely at that point, thank you very much.

However, if you were to re-gear the car so that it is at its power peak at 57 mph, you’d have substantially more torque at the drive wheels. You'd have to change the final drive ratio to approximately 4.45:1 in order to do this, but with that final drive ratio installed, you'd be at 6000 rpm in third gear at 57 mph, where the engine is making 240 hp. Going back to our trusty formula, you can ascertain that the engine is down to 210 pound feet of torque at that point (240 times 5252, divided by 6000). However, doing the arithmetic (210 pound feet, times 1.66, times 4.45), you can see that you are now getting 1551 pound feet of torque at the rear wheels, making for a nearly 32% more satisfying belt in the back.

Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, you get the best possible acceleration at any given vehicle speed when the engine is at its power peak, and, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.

Force, Work and Time

At this point, if you're getting the idea that work over time is synonymous with speed, and as speed increases, so does the need for power, you've got it.

Think about this. Early on, we made the point that 300 pound feet of torque at 2000 rpm will belt the driver in the back just as hard as 300 pound feet at 4000 rpm in the same gear - yet horsepower will be double at 4000. Now we need to look at it the other way: We NEED double the horsepower if we want to be belted in the back just as hard at twice the speed. As soon as we factor speed into the equation, horsepower is the thing we need to use as a measurement. It's a direct measure of the work being done, as opposed to a direct measure of force. Although torque and horsepower are obviously related (and each in a sense a function of the other), a good way to think about this is that torque determines the belt in the back capability, and horsepower determines the speed at which you can enjoy that capability. Do you want to be belted in the back when you step on the loud pedal from a dead stop? That's torque. The water wheel will deliver that, in spades. Do you want to be belted in the back in fourth gear at 100 down the pit straight at Watkins Glen? You need horsepower. In fact, ignoring wind and rolling resistance, you'll need exactly 100 times the horsepower if you want to be belted in the back just as hard at 100 miles per hour as that water wheel belted you up to one mile per hour.

Of course, speed isn't everything. Horsepower can be fun at antique velocities, as well...

"Modernizing" The 18th Century

Okay. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted a 3 liter E36 M3 engine in its place? Now, no 3-liter BMW is going to be making over 2600 pound feet of torque (except possibly for a single, glorious instant, running on nitromethane). However, assuming we needed 12 rpm for an input to the mill, we could run the BMW engine at 6000 rpm (where it's making 210 pound feet of torque), and gear it down to a 12 rpm output, using a 500:1 gear set. Result? We'd have *105,000* pound feet of torque to play with. We could probably twist the entire flour mill around the input shaft, if we needed to.

The Only Thing You Really Need to Know

For any given level of torque, making it at a higher rpm means we increase horsepower - and now we all know just exactly what that can do for us, don't we? Repeat after me: "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing."

Thanks for your time.
Ive always been rather amazed at the guys that assume you can just simply drop a high performance engine in any car ,and actually expect it to perform, without taking into account the cars weight or making other system upgrades to the drive train, cooling system,gearing, ignition, fuel system, exhaust and brakes, ETC.
one Of the guys I know built a 10:1 compression, performance 383 sbc, with reworked vortec heads, that allows a .550 lift cam, to be used for his 1968 impala, that originally had a 307 sbc engine and he used some rams horn exhaust manifolds,he had sitting around ,not headers, on the 383 he installed.
(His car is similar to this picture) but his is a maroon fast back with a th350 transmission, that he purchased separately some place else that was basically a stock rebuild and a 3.07:1 rear gear and 2" dual exhaust

now he installed a crane 114681 solid lifter cam

that crane cam is a great cam in a 383 when matched to a light weight car, good flowing heads, a manual transmission and a 4.11:1 REAR GEAR HEADERS, ETC, BUT NOT WHEN YOU USE THAT 3.07"1 REAR GEAR AND RESTRICTIVE STOCK STALL SPEED CONVERTER AND STOCK EXHAUST THAT STRANGLES EXHAUST FLOW.
THAT CRANE CAM,really requires a 3.73:1-to-4.11:1 rear gear and a MINIMUM 3200rpm stall converter , and at least a dual 2.5" exhaust preferably with an (X) pipe and low restriction exhaust, and its designed to allow the engine to operate to at least 6700rpm,and its not going to work well below about 3500rpm, and while the basically stock, 170cc port vortec heads are pretty much restrictive on a 383 at anything over about 5300rpm or so, he also screwed up the combo potential by installing an intake that was in bad need of port matching. the TRANSMISSION STALL SPEED was a hopeless miss match, it almost stalls the car and it won,t idle or pull until it gets rolling, you can,t expect to miss match heads,drive train gearing, use a restrictive exhaust and a cam thats designed to operate far above the rpm limitations of the heads and intake, and still expect the cars engine to operate near its full potential.
the car weights close to 3800 lbs so it might make a really nice car to cruise in, its never going to blinding fast in the 1/4 mile due to the weight and rear gear ratio, and restrictive exhaust.
He was very unhappy with the engine, until we diagnosed the problems and he made a few mods to better match the engines power curve, over time I got him to do a few tests and we found he had over 7 psi of back pressure in the exhaust at peak rpms, once he got a true 3" dual exhaust, shorty headers, and installed a 3.90:1 ford rear he got from a local salvage yard from a ford van, and installed that differential with a custom drive shaft and custom brackets, it really woke up the car.
it went from high to mid 16 second 1/4 mile times to low 14 second times which made it much more responsive
keep in mind one of the first things you do when a car won,t run as well as you expect it to is to start logically checking the basics like ignition timing, battery voltage, fuel pressure,plenum vacuum exhaust restriction,,check if the timing advances, check the throttle fully opens check for loose connections and all the other factors that might be the cause.






heres two fairly common comp flat tappet hydraulic cam dyno results in a 383 with AFR 190cc heads, there very good heads for maximizing low rpm torque and mind range power

this engines power curve, has basically peaked before 5300rpm due mostly to the short duration cam, notice the smaller cam has significantly more low rpm torque but less peak power, but keep in mind if your using a stock transmission that shifts at 4500rpm this might be what you want


this engines power curve, has basically peaked , HIGHER IN THE RPM BAND THAN THE SMALLER CAM YET STILL PEAKS before 6000rpm partly due to the longer duration cam, but still the small port heads are a restriction, but youll still need a higher stall speed converter or a manual transmission , and a 3.54:1-4.11:1 rear gear ratio, to get the best results
the larger cam engines power curve could be increased further with a larger port head that allowed it to flow more air

BTW heres a good example of what a cam swap does to a chevy 383 stroker, notice the larger duration 274 cam moves the whole torque curve higher in the rpm range, giving you more peak power but costing you low rpm torque in the exchange


now lets step it up to a 383 with AFR 210cc heads, a single plane intake,crane 119651 roller cam, 11:1 compression and open long tube tuned headers and 1.6:1 roller rockers

if you want to dump enough MONEY in semi- exotic and expensive parts into the project you obviously boost the results, you can expect, the problem of making the power is simply limited by your checking account balance. you can do amazing things with a SBC if you can afford some real good parts, and quality machine work

EXAMPLES ... A16-P1.htm

yes I,m only too well aware most of those reading the thread will never bother to read the links and sub-links but its your lost opportunity, to learn a great deal if you do ignore the linked info ... ewall.html ... lator.html









viewtopic.php?f=87&t=4788&p=13003&hilit=calculators#p13003 ... torque.htm

POWER (the rate of doing WORK) is dependent on TORQUE and RPM.
TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM, by the following equation:

HP = Torque x RPM ÷ 5252

Figure 3

Note that, with a torque peak of 587 lb-ft at 3000 RPM, the pink power line peaks at about 375 HP between 3500 and 3750 RPM. With the same torque curve moved to the right by 1500 RPM (black, 587 lb-ft torque peak at 4500 RPM), the peak power jumps to about 535 HP at 5000 RPM. Again, moving the same torque curve to the right another 1500 RPM (blue, 587 lb-ft torque peak at 6000 RPM) causes the power to peak at about 696 HP at 6500 RPM

Using the black curves as an example, note that the engine produces 500 HP at both 4500 and 5400 RPM, which means the engine can do the same amount of work per unit time (power) at 4500 as it can at 5400. HOWEVER, it will burn less fuel to produce 450 HP at 4500 RPM than at 5400 RPM, because the parasitic power losses (power consumed to turn the crankshaft, reciprocating components, valvetrain) increases as the square of the crankshaft speed.

The RPM band within which the engine produces its peak torque is limited. You can tailor an engine to have a high peak torque with a very narrow band, or a lower peak torque value over a wider band. Those characteristics are usually dictated by the parameters of the application for which the engine is intended.

An example of that is shown in Figure 4 below. It is the same as the graph in Figure 3 (above), EXCEPT, the blue torque curve has been altered (as shown by the green line) so that it doesn't drop off as quickly. Note how that causes the green power line to increase well beyond the torque peak. That sort of a change to the torque curve can be achieved by altering various key components, including (but not limited to) cam lobe profiles, cam lobe separation, intake and/or exhaust runner length, intake and/or exhaust runner cross section. Alterations intended to broaden the torque peak will inevitable reduce the peak torque value, but the desirability of a given change is determined by the application.


What I like is, building cost effective,easily duplicate-able engines, from off the shelf components if what I need is available, if not I have zero problem fabricating some components or modifying whats available if required,engines that use mostly built from well matched correctly fitted components. I like having total predictable control on a valve train components and long term durability, with low maintenance and in most cases large displacement high compression engine combos
I prefer to keep the piston speeds under 4300feet per minute , and Id prefer to keep the compression as high as I can , simply because its generally going to make for a more responsive combo with higher torque in the useable rpm range.
now in most cases thats engines of 400 cubic inches or larger displacement, and when I can 11:1 or higher compression, so 7000rpm is about where Im comfortable limiting valve train speeds, and I have zero issues building bigger displacement combos that might never see 6500rpm.
given the choice Id gladly give up that last extra 2%-5% of potential horse power in exchange for an added 20%-to-50% greater engine life expectancy, which is in many cases a choice you ARE forced too make
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antiford said:
Anybody think I could gain anything from the big voodoo hydraulic flat tappet #10120705 by increasing the rocker arms to 1.6's and using lightweight Lunati racing lifters?I have the Dart 215 heads and cannot afford a roller cam but I intend to keep the 215's for future upgrades if things get better.Is 500lbs. torque possible with this cam in a 406 sbc?I like having my cake and eating it too so I don't care for solid cams because I'm getting old and lazy.
if you don,t think use of the correct valve springs and rockers matters heres the dyno results on a 496 BBC chevy engine with a new set of valve springs and roller rockers, obviously if correctly selected,they can make a difference


your likely to gain a few peak hp swapping to 1.6:1 rocker ratio, but I doubt the effective change will be close to what you might get with a good solid lifter cam or better still a roller cam.
a flat tappet solid lifter cam, correctly matched to a set of springs designed to operate with the cam, could easily add an additional 500-1000rpm over what a hydraulic flat tappet cam can provide, a solid roller or hydraulic roller will not only add a few rpms but add additional port flow if properly set up with the correct valve train components, because of greater valve opening area under the curve, allowing the port to breath more effectively over the whole lift curve


viewtopic.php?f=52&t=3802 ... 6/10002/-1

related threads and useful info
you might be amazed at how much-related info,
is previously posted on this subject
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yeah! it could easily take you several days of reading time to wade thru the links and sub-links,I've posted above and below , but Id bet you'll save hundreds of dollars and weeks of work and avoid a bunch of problems if you do, simply take the time required.!
the basic secret to building a good combo is to think thru what your intended goal is as to power level, durability and cost limitations and then make reasonable matching choices in components, and do a decent job of carefully assembling the components with the correct clearances, a fact that gets over-looked far to often, in the rush to either save money or complete the build rapidly.

















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I'm at the cam select phase and, although I know the 327 is not a low RPM torque generator, I'm attempting to get the most out of the 1000 to 4500 RPM range. What I'm working with is a stock '65 327/300, carb on down to rams horn exhaust. The only component to be changed is the cam.
Details: 600 AFB, 3844459 iron intake, block (.030, decked), 461's (1.94, 1.6, surfaced), 2" rams horns, 2 1/4" dual exhaust with turbo mufflers, stock TC & Powerglide, 3.55 diff.
At .038 quench she's pressing an SCR of 9.81:1. As best as a calculator can offer I'm targeting 7.5 to 7.9 for DCR. If I decide to tackle the heads and sanitize the combustion chamber I'll shoot for the 7.9 DCR with hopes of still using 91 (or less) octane. It's looking like an IVC of 63 to 69 (dur. 272 to 282, ICL 112) is where it needs to be. I was thinking overlap in the 45 to 55 range with valve lift around .435 to .455 and @.050s of 205 to 215. Original thoughts were to shoot for a 260 to 265 duration range but the numbers (on paper) don't seem to allow it (Please advise if any of my assumptions are off base).
Now the question would be: Given the stock intake and exhaust along with conservative components and operating range would the advantage go to a single or dual pattern grind? Might cleaning up runner flashing and performing a minor pocket port on the exhausts make a difference to this decision?
Any insight much appreciated.

major factor's you really can,t ignore is the requirement too match the compression ratio to the fuel octane, the cam timing, intake port flow rates, exhaust scavenging and quench

example of (engine building" vs parts assembly)


Id bet 80% or more of the people assembling parts have never checked most component clearances ,
except in most cases for ring end gap and bearing to crank journal, as thats almost mandatory.
things like,
piston to the cylinder head (quench)
piston to valve,
rocker slot to rocker stud,
connecting rod to cam lobe,
connecting rod to block skirt,
piston skirt to crank counterweight,
cam button to the timing cover,
spring bind height,
rod side clearance,
thrust bearing clearance,
ring end gap and piston slot back clearance on rings.
piston to bore clearance.
pushrod to the cylinder head, or guide plate,
crank journal taper and concentricity and surface smoothness
cylinder head surface and not being warped
cleaning out all the threaded holes with a tap.
sonic testing bore walls
having the block , crank and heads checked for micro-cracks
verifying the oil pump drive shaft has about .050 clearance with the distributor fully seated,
replace and shim distributor gear with new cam installation
verify oil pump relief spring function, test to ensure it opens at no higher than 70 psi
checking for crank straitness.
verify crank journal to counter weight junction has consistent radias
verify head gasket opening is at least .030 larger than bore diameter all the way around bore circumference
verifying main cap concentricity and shoulder depth.
verify pushrod length and valve train geometry.
timing chain slack, and/or lack of clearance to the timing cover.
verify theres no crud inside push rods or block oil passages.

verify the block oil passages and bearing oil holes align properly (correct and bevel as required)









notice how the rod bolts come close to the cam bearings as the pistons reach top dead canter in the bores



reading links and sub-links will take days ,
but it's sure to save you hundreds of dollars ,
and weeks of wasted effort.

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