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Discussion Starter #1
In a mildly centrifugally boosted application (5 - 7 psi) how important is a quench pad/area in the combustion chamber as compared to an open chamber.

I know open chambers are a really, really poor design and susceptible to pinging, so that would definitely lead me away from using them, especially in a boosted environment.

However, say you have some open chamber heads that are basically new and ready to run, but you can get some aluminum closed chamber heads for around $900 (but they are the bottom rung of heads: ProComps :beek: ).

Cr’s with either heads would be identical at around 9:1. I can’t run a closed chamber OEM head because my cr would be way too high for any boost. And the OEM closed chamber heads are not cheap!!

So, my question is: With a proper fuel/timing tune, can an open chamber head support boost without losing gobs of power due to retarded timing?
 

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It depends what you are looking for out of the car. Open chamber heads are great for high-rpms, but will have problems with uneven mixtures down low. That is what causes the reduced power at lower rpms, not the lower timing. Actually, the open chamber allows for the flame front to expand out more evenly, and therefore it starts pushing on the piston sooner, and that is why you get pinging running the same timing on an open chamber head as on a closed chamber. You won't lose power from that though because even though you are firing the spark plug later, the flame front moves faster and starts pushing on the piston about the same time. Now that the explanation is out of the way, we come down to what you should do. If this is a street car with a centrifugal blower, you won't be happy with the open chambers. If it is an all out drag car with a centrifugal, keep the open chambers because they will actually make more power in the top end. If you are putting a roots blower on this thing, then keep the open chambers because you already have them, and any low-end torque you would lose from the open chamber heads you will more than make up for with the blower.
 

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Discussion Starter #3
I didn't know about the open chamber being good for higher rpm, since nothing I've ever built was for rpm's over 6K. And everybody wants the closed chambers.

I guess I'll have to start saving up my coins for the aluminum heads since this is for my 73 Cougar and its 351C. It is definitely not a race car by any stretch of the imagination. :D

I have a 4V Cleveland with a B&M blower (164) in it in my shop, but I don’t want to put that in the Cougar because it wasn’t available back in the early 70’s.

Thanks for the explanation. :thumbsup:
 

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After assembling a few sets of pro comps I would stay far away from them unless they have cleaned up their act. Nothing fit right on the ones I did and the valve job left a lot to be desired.
 

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Discussion Starter #5
After assembling a few sets of pro comps I would stay far away from them unless they have cleaned up their act. Nothing fit right on the ones I did and the valve job left a lot to be desired.
Yeah, I've heard nothing but very bad things about ProComp. The general consensus (on the 460 boards at least) is that by the time you "make them right" you should have just bought the higher priced, better flowing units.

Decisions, decisions….. :bawling:
 

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I have a 4V Cleveland with a B&M blower (164) in it in my shop, but I don’t want to put that in the Cougar because it wasn’t available back in the early 70’s.

Thanks for the explanation. :thumbsup:
What do you mean by this? The C was available in 71, 72, and 73. In fact, those were the only model years they were available.

SWS
 

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Discussion Starter #7
What do you mean by this? The C was available in 71, 72, and 73. In fact, those were the only model years they were available.

SWS
True, but the B&M style supercharger was not, which was what I was referring to. The “theme” of the car is that anything that goes on it (and can be seen) has to have been available before 1976. Basically what someone would have been able to do within a few years of buying the car new.

So from a supercharger standpoint I think the only thing that would have been (readily) available is the Paxton centrifugals, or a home grown roots diesel GMC supercharger setup.
 
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