need help to I.D. some pontiac heads

Pontiac combustion chambers are fully machined as opposed to a Chevy that is a cast combustion chamber. Opening them up involves machining them larger for more volume. It does not affect port flow other than possibly unshrouding the valves. By making the chambers larger (more volume) you are lowering the compression ratio. Determining the amount to machine from the chambers requires measuring the piston deck height and calculating the volume of the cylinder above the piston at TDC, including the compressed volume of the head gasket. Then a final chamber volume can be determined to achieve the desired CR.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Yes it decreases the compression ratio.  
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why would I need to decreases it?does the ram air 3 heads have to much CR for todays fules???  

Yes the 12,13,48,62 or 670 heads have right around 72-74CC chambers and that will give you right around a 10:1CR which is too high for pump gas.  
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how did the cars of the day run on these heads??did they have diffrent octane fules back in the day or waht???also is there any heads that would give me around 9.5 stock could I use a thicker head gaskit to reduse compression??
thanks!  

Gas just is not what it used to be.  
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what would happen if i was to run pump gas with these heads with 10:1CR???  

what about runnin 48 heads with a larger cam which i was told  will bleed off more cyl. pressure, therefor makes dynamic compression lower, and lets you run more static compression.
???what do you think of this???
thanks  

You will have detonation problems and it will eventually cause damage.

Running a large cam will only bleed off some compression at idle and low speeds so unless you will be idling around town all the time it will not help.
Unfortunately there is a lot of misleading info out there like that which are just band aids.  
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ok thanks what if someone had a all orginal 69 gto juge with a 400 and ram air heads they wouldint be able to run it on todays gas???
thanks  

P-man8 is right, the big cam, high CR myth doesn't take into account that when you accelerate under WOT, the octane requirement goes back up to what the engine really needs. Fuel back in the day was available up to 110 octane versus our 92-94octane today. It no longer makes good sense to build high compression engines for the street, since cam design has come so far in 40 years that we can make the power without the compression. Of course for all out racing engines that will run on racing gas, it still makes sense to get everything you can and that means squeezing it hard!
Steve  
A little help... 'cause we don't all have to learn the hard way!

so it seems the heads I have the (94's) would be better then the later 400 heads as cr is 8.5 opposed to the 8.1 that the later trans ams have the car pulls very hard off the line old owner says it has around 425hp which i find it hard to belive with thoes heads found out it does have a forged crank and pistons and unknow work to heads and unknow cam  it seems as im prlly best sticking with these heads and leaving them alone and goin with somethin else to give it a few more ponys maybe a holly 750 double pumper and chukin the holly 670 street advn carb?
thanks  

As far as I know, there are no forged cranks for 400's, unless it is an aftermarket one. Someone could have installed larger valves in the 94 heads. Most d-port heads flow about the same given the same valve sizes. The 670 should be adequate, you probably won't see any big difference with a 750.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Ya if the heads still have the small valves in them the 750CFM would probably be to much.  
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