Don Terrill’s Speed-Talk

Been doing some research on old cleveland prostock heads. The prostock boys then were approaching 800hp . Gliddens fairmont running in the 8.4 range. The heads of that era (i happen to have a set) flowed in that 355 range however the csa is quite abit bigger than stock cleveland and or newer style castings. Looks to me the mcsa and csa is as important or even more important than flow. Is that the case?

I am by no means a cleveland expert, not an expert on anything really. But the flow per square inch of cross section on these heads is always lower than the newer heads, and relates to airspeed. So the target mean airspeed on these heads seems to be around 10-15% lower than a typical inline small block head of today. That bein g said, they seem to run pretty darn hard despite having 'too large' of a cross section for the flow. So I would probably go out on a limb and agree with the assessment that as far as the old cleveland stuff, the cross section is probably more important than the flow. Just my observations.

If your able to get your peak power made in 1000 rpm or less band then the csa can exceed what's concider the way to go it would seem.
I know I am not the only one who has got a car down the 1/4 mile faster by cutting back Intake air flow which is what you speak of here in a way.

And this flow reduction was done by means of NOT making the port smaller to boot!

IMO better to have a port flow less and resist reversion than to have a port that flows more but back flows.

I always wondered how some of these old heads performed so well. Now its kinda interesting to see. I replaced a new set of heads from a old ported cast only to see very minimal gains. Under 1/2 tenth. The edge in flow went to new head and even had smaller csa. Which was supposed to enhance airspeed. The alloy heads wouldve lost energy in cylinder no doubt.

Steve.k wrote: ↑Wed Jun 06, 2018 2:47 pm I always wondered how some of these old heads performed so well. Now its kinda interesting to see. I replaced a new set of heads from a old ported cast only to see very minimal gains. Under 1/2 tenth. The edge in flow went to new head and even had smaller csa. Which was supposed to enhance airspeed. The alloy heads wouldve lost energy in cylinder no doubt.

Maybe there was really zero gain from the heads, but the loss in weight was the gain?

Frankshaft that doesn't reach the finance department ok!! You likely right. Lol

Steve.k wrote: ↑Wed Jun 06, 2018 3:37 pm Frankshaft that doesn't reach the finance department ok!! You likely right. Lol

I bet the new heads did make more power in the rpm range the engine never sees though

Down low yes smidge better.

Measured the mcsa on old pro stock head was 2.98. The stocker runs 2.54.

Did that 14.7 percent gain in port area over the stocker make for the same gain in performance or air flow?

Well i have some stock e heads that flow more cfm at .600 that the p/s heads at .800. However the p/s heads made just short of 800hp.Dont think the stock eliminator heads will get there.Stockers never gonna happen.