I've been doing some reading lately and there seems to be preference towards the open heads (b/c the "tub" design restricts flow?). Anybody have real-world experience?

Vince,
I run open chamber heads on my 396. I don't know if there is alot of difference between the two styles. If the compression ratio is kept the same. Now, if you put an open chamber head on a motor that had closed chmaber heads the drop in compression will probably have more of a negative effect on power more than offseting any gains from improved flow offered by the open chamber design.
I'm going to Cecil County tommorrow, first time out this year. Why not bring that '69 down for a run?

i have and continue to run both styles of heads...........and i have done some back to back testing.........last year i changed heads on my z28 396 bbc........and it slowed down with really no other changes .......granted the compression fell way off......but the flow dont make up for it...........

i have ran the bath tub closed chambered heads into the tens with back yard port work and 2.19/1.88 valves so i know they will go that far with just some basic clean up and valve job that is done right.........

the open chambers sound right in when you read about them flowing better.......alot has been printed.....gm's way to help clean up the air back then.......and to gain a few extra hp........but for me unless everything is just perfectly the same when testing both heads i could see the open chambers making more power.........but for my real world it has not made squat of a difference. i run what i have when i need it.......both are good designs in there own right.......

something like this can be tossed back and forth there just not enough difference in the real world i think to make a difference....you can make either head perform with very little work...........

at least 10.37 @ 3900lbs.

Imho, you get a better bang with the closed chambered heads for the same compression ratio b/c there will be less volume to burn as well as a lower dome to burn around!!

BUT they are dirtier from an emissions standpoint b/c there is more cold combustion chamber wall to quench the burn next to the combustion chambers walls..

AND this is why GM changed in the first place!!

And they even carried it to the extreme when they squared off the exhaust side quench to match the intake side's line later on when the smog reg's got tighter....

It just so happened that open chambers also unshroud the valves so they suck better but IMHO, their piston domes don't allow them to burn as eff. as closed, but dirtier emissions producing chambered heads do..

And I'm not trying to start a "which one is better" thing here either so I am outta here before it starts.......

pdq67

8.46 162+ in the old super Comp car. Stock set of 291s with a TRW motor and a flat tappet cam. The most trouble free and easiest combo I ever ran in a race only car.

I should of asked what was the difference in performance w/the same compression - sorry!

Originally posted by Vince g:
I should of asked what was the difference in performance w/the same compression - sorry! I highly doubt you will find anyone that has real numbers..seeing that besides a head swap,a piston swap would be required to maintain the same compression.Also,to be valid,the castings would have to be unported as well.All I know is,I'm happy with my closed chambered 454..hard to argue with a 4000# street car that runs low 13's and touched the high 12's with 2.73's on DOT tires thru the exhaust..and the other extreme would be Ed's ride..hard to argue with a 3900 lb. car that runs low 10's smile.gif We both use the same heads,but mine are totally stock.

We can refer you to many sources, but the one that sticks out in my mind's eye is an article on compression/quench done by Vizard in one of the magazines last year ( it'll come to me if someone doens't beat me to it).

Anyway, it's common knowldege that more effective combustion occurs with a smaller quench area, more even, better flame travel. Therefore small chambers with minimal 'contouring' of the piston top is the preferred method of combustion vs. a large chamber and big dome slugs.

Your question was answered above. 10.30s at over 125mph, meaning its making somewhere in the range of 600 ponies. BTW, any car running that quick is not doing it SOLELY on the cylinder heads. That's a well engineered car. What is the combustion process worth in that case is quite debatable. It might be measured in hundreths or, in a tenth or two, I should think.

Nevertheless, it won't hold you back at all. Getting the desired compression might, as piston selection is a bit more limited using cc heads, but not much of an issue in a standard 454.

Whether these are better for larger cubic inch applications is what I'm curious to know. I **suspect ** that oc heads are prefferred here as chamber unshrouding and valve size might more than offset any efficiencies gained by better quench. Specifically referring to bores sizes larger than 4.30"

** Suspect **, don't rightly know. I KNOW that I'm much more comfortable running 10.51:1 on the street with smaller 112.5cc oc chambers than I'd be with larger domes and larger 118 cc chambers.