Don Terrill’s Speed-Talk

500 inch drce3 headed engines making peak power at 9700 with 275 duration. 290 inch stock headed engines making peak power at 7500 with 282 duration and the cam dictates rpm?

CGT wrote: and the cam dictates rpm?

Yes, when there are no other restrictions.
When you have a big enough port, exhaust, intake, and carb, the cam duration controls the peak HP rpm.
In fact, there is a direct mathematical relationship.

CamKing wrote:

CGT wrote: and the cam dictates rpm?

Yes, when there are no other restrictions.
When you have a big enough port, exhaust, intake, and carb, the cam duration controls the peak HP rpm.
In fact, there is a direct mathematical relationship.

So you can make the Prostock peak a couple thousand higher, or a few thousand lower?

CGT wrote:

CamKing wrote:

CGT wrote: and the cam dictates rpm?

Yes, when there are no other restrictions.
When you have a big enough port, exhaust, intake, and carb, the cam duration controls the peak HP rpm.
In fact, there is a direct mathematical relationship.

So you can make the Prostock peak a couple thousand higher, or a few thousand lower?

I can easily make it peak a few thousand lower.

And higher?

CamKing wrote:

CGT wrote:So you can make the Prostock peak a couple thousand higher, or a few thousand lower?

I can easily make it peak a few thousand lower.

How many less degrees of duration would that take to lower peak TQ by 2000 rpm and/or peak HP by 2000 rpm?

Rick

Rick360 wrote:

CamKing wrote:

CGT wrote:So you can make the Prostock peak a couple thousand higher, or a few thousand lower?

I can easily make it peak a few thousand lower.

How many less degrees of duration would that take to lower peak TQ by 2000 rpm and/or peak HP by 2000 rpm?

Rick

It depends on the Bore, Stroke, and Rod Length.

CamKing wrote:

CGT wrote: and the cam dictates rpm?

Yes, when there are no other restrictions.
When you have a big enough port, exhaust, intake, and carb, the cam duration controls the peak HP rpm.
In fact, there is a direct mathematical relationship.

I'm curious how the intake ram filling and the exaust max excavenge RPM relates to pk tq and pk hp ;

Some EMC engine power curves with three tq spikes in the curve with almost identical peak #s comes to mind.
Maybe there was more than one single part dictating the pk tq?



Just asking not trying to be smart.

I see engines make peak power at different rpms, with the same displacement and cam size, very frequently. No doubt if you keep all the other variables the same, then cam size has a direct relationship. It's not even in doubt in my opinion. My street 432 cid engine peaked at 6200 rpm with a 240/246 @ 0.050" solid flat tappet cam.

JMO,

paulie

CamKing wrote:

Rick360 wrote:
How many less degrees of duration would that take to lower peak TQ by 2000 rpm and/or peak HP by 2000 rpm?

Rick

It depends on the Bore, Stroke, and Rod Length.

Let's pretend I know it is this ...

Bore = 4.700"
Stroke=3.600"
Rod=6.000"

Rick

CamKing wrote:

CGT wrote: and the cam dictates rpm?

Yes, when there are no other restrictions.
When you have a big enough port, exhaust, intake, and carb, the cam duration controls the peak HP rpm.

"Resrtiction" is kind of a relative term. All engines are restricted to their current power level and rpm by something.

So if the induction tract is sized for 9500 rpm, and the cam won't let the engine make peak power there, isn't the CAM the restriction?

I guess it would be true to say IF you have a big enough CAM, exhaust, and carb, the induction size sets the rpm.

Randy

That sounds true. Just look at long tube runner TPI sbc's. Very long intake tract and the cross sectional areas arent large enough to support alot of RPM on most 350+ inch motors. Seems any cam you throw in them even if the heads are large, they wont peak much past 5000 rpm if that. Most in the 4800 range. Hp may hang on for several hundred rpm without falling off but does not rise any more. Intake is the restriction. Now if you open up the base to large enough cross sections, and have a runner with tube diameter thats large enough to pass some serious airflow and also not be a cross sectional area limitation, you can pull alot more rpm. Also can take advantage of the intake ram tuning, as you will find the total runner length on some of those systems actually are tuned for 6000 rpm+.

So in that sense the cam would not control rpm range.

The camshaft is # 1 in the hierarchy in my book. Just look at some of the stock BBC’s from yesterday with the huge square port heads ….say a 1970 LS6.
Peak torque in the 3000’s rpms??…. Peak HP in the 5000’s rpms?? What is wrong with this picture?
Camshaft!

Like said by Camking, if the intake and heads are large enough the cam will dictate. But you wont get a 170cc 1.94 valved stock iron sbc head on a 427" sbc to peak at 8000 rpm... I dont care what cam you put in there.

Yup, it's a huge oversimplification to say with this displacement motor and this size cam you will have this rpm range. Pretty much useless without more information.

JMO,

paulie