[harry k]

overall what i learned here is : a street / strip car with 455 to 462 ci pure pump gas up to 91-92 octane (no EMC exotic stuff) compression ratio no more than 10.5 (alluminum head)& cams up to 240 does NOT require a head more than 270 cfm to make it the best combo as we call it .

[speedshopmike]

harry k, i disgree:
what we've learned here is little to nothing.
i'd say the major point is that there are no hard and fast rules, and a good combination will beat a bad one with "better" parts.
we build small fords all the time with 300 cfm heads - they're a 150 cubes shy of a routine poncho motor.
there's a ton more to this then just flow numbers - far, far more.

[ponjohn]

Originally Posted by harry k

overall what i learned here is : a street / strip car with 455 to 462 ci pure pump gas up to 91-92 octane (no EMC exotic stuff) compression ratio no more than 10.5 (alluminum head)& cams up to 240 does NOT require a head more than 270 cfm to make it the best combo as we call it .

I would agree with this - I have: 9.5-1, 462, 220cfm d-ports and run 11.90's at 3680 race weight.

[70 Lemans]

This is my first time ever build. (Not in service yet) I’ve been wonting to build a decent Pontiac engine for over 20 years. Now I'm not sure if I went about it the right way.
Seems the lack of above knowledge cost me.


69 400 Block .030 over, eagle stroker kit, ported 87cc CNC e-heads 305 310 cfm, port matched RPM, Cliff’s q-jet, comp cam Hydraulic roller 236/[email protected] 585/600 lift 110 LS with 1.5 rockers, butler timing chain, butler valley pan with pcv, 3500 stall with 3.55’s gears Lifter bore brace and 4 bolt billet mains, 1 7/8 dougs headers Race weight is approximately 3700lbs Looking for 11.5 Et
Very upgradeable but overkill.

90% street 10%strip

[Bruce K]

70, Looks pretty f'n nice to me! Good luck, let us know how it runs.

[Skip Fix]

Jim I've read Vizards articles. He HAS mapped velocity and measured it. I don't think we have on Pontiac heads.few shops I've been to have a velocity manometer. I've read other experts that agree in some areas and disagree in others. His articles often are abbreviated in different magazines. The same general articles appear in different magazines with different additions or subtractions. Many others now use the CSA(cross sectional Area) instead of port volume to determine how a motor will respond.Intake runners or exhaust pipe cc are just port extensions so they add more variables that CSA. A longer dual plane runner wil make a different total cc than a shorter single plane, but shorter than a M/T crossram.In fact most experts now use that much more than port cc for intake as well as exhaust.

The Pontiac engineers did NOT loose streetability adding 30cc intake port volume. If that is the case why did these motors not loose torque and street manners? Were they wrong? I'll bet they spent alot of devlopmental time and $ testing a totally new port and chamber. Were the factory ratings wrong and really the HO/SDs had less power? They would have to using only port volume/velocity theory we are here.

Yes Lynn uses high rpm compared to your 460 motor but less that other brands in his group. That still does not refute the fact that the cylinder head experts feel too much velocity is bad in whatever rpm range you run for the reasons he and I both mentioned.I believe even Vizard has mentioned that somewhere.

Let's ASSUME your D port motor has 50 more ft lbs at 1000-1800 than my E head motor, but at 2000 its only 10 more, at 2500 I'm 10 above and climbs greater diffeence from there. How much driving/acceleration is in the 1000 to 2000 range? How fast does the motor acelerate through that range? Is the Kaase motor with its huge ports and 100ftlbs over both of our motors at 2500 going to be a no streetable? Maybe because it roasts the hides too easily.

You are also leaving exhaust ports totally out of the equation. Most experts do NOT,including Vizard! It is an average of intake CSA rpm range and exhaust CSA rpm range that determines where the motor likes. What were the CSAs on the intake ports, exhaust ports, exhaust port ccs? All of those also are a big factor.

You still miss my point, there were many other things in your test besides the intake port size that could have affected performance that may or may not affect other motors performance in a similar manner.

Are you stating that port shape, chamber shape do not affect mixture filling in the cylinder but only size does?

[Ron H]

Well, I have learned a few things.
1. is I am making at least 75 more RWHP with my 310 cc KRE 74 cc d ports over my 6x-4 heads. Mainly because,the flow went up and they have a better chamber design. The CR helped a bit as well. I was thinking that I may have lost some throttle response earlier. But with a bit more tuning yesterday on the way home, the low cruise throttle response is there, there is just so much more power in heavy part throttle and a huge amount more power in WOT.
2. I think my cam actually may be better for these heads and may have been a bit big for my old combo as my CR was only 9.4 to 1 and they only flowed 240ish. If the CR is higher 10 to 1 or so and the heads flow 240 @ .550 lift that cam is spot on.
3. Higher lift cams without a huge amount of duration and overlap can produce great torque and HP numbers providing you have the heads to use it.

[Junkyard Dog]

Originally Posted by Jim Hand

And it also was obvious that it was a loss of low and early mid range power . . .
Jim Hand

How low? Doesn't your convertor flash to 3,500 rpm?

[Skip Fix]

Good job tuning Ron! I'm sure there is more there.

Jim you have refined your combination from the air cleaner all the way out the exhaust so well you can run much faster than most other guys with "similar" parts. I'd bet you could dominate the stock FAST classes if you decided to go there! You can do more with less than most of us.

I'm a little less patient and dense so I need the extra buffer of more airflow to help me get there. My combination would be easily duplicated by others as I've gotten there with less tuning time. The only refined piece I have is my "high port" welded Torker II. For me 6000 isn't a big deal.

It's all about your goals for your car using the same general theory to get there.

[gearbanger]

Originally Posted by Jim Hand

Guys,
What and where is the "one point more CR" rule listed and documented?

I am sorry that the technical facts I (and many others) have presented about the effects of different port sizes on engine power are being disregarded. I fully understand we don't like to give up pre-conceived concepts about how to go fast.

I will close my portion of this discussion with this comment:
The next time anyone wonders why my 4070# wagon with 3.31 gears, a mild cam, and a Q jet can possibly be competitive with lighter cars running much higher flowing heads and larger cams, you may want to reread some of the facts I have posted and referenced. My car doesn't just magically run what it does by following pre-concieved ideas and "rules" that have no basis.

I have tried to help others understand the subject, and that is all I can do. I don''t have time or the inclination to argue about material I have tested and confirmed.

The KRE heads I bought and ran are long gone - I learned and confirmed all I needed to know about the effects during those weeks of trying to make them work at least as well as what I had.

As always, we should each build our cars exactly as we want them, regardless of what others say. So keep those Pontiacs running!

Jim Hand

Jim, I'm not disputing you. All I am saying that you had your iron heads maximized for pump gas. You did not have the KRE heads maximized for pump gas. So therefore you sold them short.

How do you know that a bigger port would slow your car down? Have you tried a bigger port in your 6x heads and had to go back down? I am simply saying that if you would have taken the compression on up to the limit of 93 like you are now with your 6x's, then you would have out performed them with the KRE's. How can you dispute that? Did you test it and prove that it is not the case?

And why do you keep asking about the one point rule? It's not a rule, it's a estimation on how much more compression you can run on the same fuel with aluminum versus cast iron. That is well documented in hundreds of aluminum headed combos of all makes. Have you never heard of this?