Ok guys, I am starting to look at some different cylinder heads for my next engine (I have a 383 stroker short block being built right now) seeing as how my old one has blown up Anyway, after doing some thinking, I have decided on trying to attain the 500HP/500TQ mark with this new motor. What I would like to know is the formula for computing engine/cylinder head CFM flow ratings, and how they compare to POTENTIAL engine output. For example, lets say that a cylinder head that flows 285 CFM @ .500 lift measured @28 in. H2O would be good for, and sufficiently support X amount of HP and TQ. That way, I can properly decide on which heads/cam I will need to use without having to go larger/more radical than required. I would also like to note my RPM range for this engine. I don't want to have to spin it past 5500 RPM. Now I know most people will think that I'm nuts, and won't make any power unless I spin her up to 6500+, but let me remind you of one thing. HP is a measurement based off of torque. TQ multipled by RPM divided by 5252 equals HP @ that RPM. This formula is always the same and never changes so......

If I build my engine to make it's peak torque at 5200-5300, then my horseower will be THE SAME at roughly the same RPM. Let's say that I made 500 ft. lbs of torque at 5200 RPM, then by using the above formula
you'd get this....

500 ft. lbs. x 5200 / 5252 = 495 HP

OR if I ran it up by another 100 RPM...

500 ft. lbs. x 5300 / 5252 = 504.6 HP

In a perfect world that would be ideal, but there are other factors that calculate into the whole thing such as CFM flow, intake/cylinder head/camshaft configuration etc. especially the amount of flow at higher valve lifts(meaning that there isn't enough extra airflow through the head at higher valve lifts to support the extra wanted horsepower levels, so why stress the valvetrain? I'm just looking to get close.

 

For a ball park figure most use the muliplier of 2.056 times the cfm rating of the head. So in your case using the 285 figure that comes out to 586 hp at 100% VE. I would use nothing less than a 195CC head on that motor and a ported one at that.

Couple of thing to consider. One is you might want to raise the rpm level to around 6000 rpm. Two, there are a lot of good cams on the market these days so do a lot of research. Remember that lift is your friend when searching for horsepower. Three, lots of good heads on the market. Look at Trickflow, Dart, AFR and some others. There has been a lot of improvement in the technology of the heads. You might want to condsider something as large as 215CC or somewhere in between.

Last, you should have no problem reaching your goal with a properly assembled motor. Do some research on dynamic compression ratio and quench. Good luck with your build up.

 

Where did you get 2.056 as a multiplication factor? I have never heard of that before.

Actually, I plan on using a set of Dart Pro 1 aluminum heads, with 72cc chambers, 2.08/1.60 valves with a 230cc intake runner for optimum flow.

 

You're taking these head flow/power potential formulas out of context.

You won;t make 500hp @5000rpm or 5500 with a 383ci motor using pump gas.
(10:1 compression) Using your method of working out the combo. Not with any kind of streetable real world combination.

You can/ could make 500hp at a higher rpm thou. Need to reevaluate your goals. lay off relying on these magical simple math formulas and you'll be a lot better off. They assume a perfrect motor with perfectly tuned induction and exhaust, no accessories, an assumed rotating friction coeeff. and no mufflers
and perfect air. Not near the environment a real car operates in every day.

You can build a rocking street 383 but you have to take your head out of the sand first.

Joe Sherman sells a streetable 383 that make more than 500hp. check it out.

Joe Sherman Racing - Welcome

 

OK, I just took a look at Joe Sherman's site. The 383 engine that he build is very impressive, but did you take a look at the dyno sheet that the engine produced??? Here it is...


Take a look at where the horsepower and torque lines intersect. It's an awful lot close to about, say 5252 RPM wouldn't you say? Trust, me I believe everything that you said, that there are too many factors involved to get an accurate indication of what an engine will make power wise. But what I do know is that I want to build as much torque out of this motor and have it come in at the 5200-5300 range because I know that my horsepower will be similar.

 

Re read fbird's post. That motor was most likely tested with no accessories, perfectly tuned with perfect air, open headers, etc. You need to ask yourself if you want a dyno queen, or something that performs the best for the type of driving you do. Also what has been done to the car your putting it in? Your gonna have to budget for suspension parts, chassis parts, a better transmission, and all the other stuff thats going to come with that motor.

 

I got the 2.056 figure off the internet sites. Stan Weiss uses the same number on his cylinder head chart. See http://erols.com/srweiss/tabledc.htm

 

Well, I certainly don't want a dyno queen because they make Supras for that! The reason why I'm set on the 500HP/500TQ thing is because I figured that with a properly setup chassis and suspension, I *SHOULD* be able to get the car into the 11's ie. 11.9x. The car will have boxed subframe connectors, 34mm and 24mm solid swaybars, tubular adjustable rear LCA's, tubular adjustable torque arm with pinion angle at about -2 degrees, tubular adjustable panhard bar, 3.5 in. alumimun driveshaft, Currie custom 9 inch Ford rear with 4.11's and posi plus a bunch of other stuff. It's hard trying to build a car that is dual duty, something that performs very well at the track, but then being able to drive it home and tool around in it everyday. The only thing that I am worried about breaking is the transmission. I have a factory WC T5 out of a 92 Z28 and the extra torque made by the 383 will probably smoke it. Sure I'll take it easy on the trans for a while as I break in the new engine, but it sure won't like WOT.