I have a 350 Rocket in my 72 Cutlass Supreme getting rebuilt. 1 of my #7a heads is cracked and I'm having it replaced. The shop has a set of #5 heads already in hand off a 73 Olds engine. Will the #5 heads work ok on my 72 350 Rocket? Just want to make sure before I tell him put them on...

 

Yes. #2 through 7 heads are interchangeable. A 73 motor would have #8 heads from the factory however, and those have bigger combustion chambers and would not work as well. As long as it IS a #5, it will be just fine so long as your machine shop compensates for the different springs and retainers.

 

A #8 head on 1 side of the engine would result in lowered compression in 1 cylinder bank.

 

The #5 heads are not unleaded fuel heads so the seats would not be hardened originally.

 

just a thought, As the maniac said they are not hardened seats, so if you have hardened seats done by the machine shop perhaps they can also upgrade to the larger 2.00 inch??? w-31 size intake valves??? also you will up the compression a decent amount??? as the 8's were smog heads

 

The olds faq page says 5's are 64 cc and 8's are 79cc????? so a gain in compression:-) just as they are...

 

I always replace the seats when rebuilding the heads. Hardened seats are only used on the exhaust, 2" is on the intake. IMO, no need for the big intake valves without port work. Also, you are missing the point. The guy has 1 bad 72 7a head which has a 68cc chamber and is asking if he can exchange it for a #5 head, which as "J" pointed out, he can.

 

Again, he is NOT going from a #8 to a #5.

 

Sorry for the confusion, ( I seem to do that a lot )

and thanks also for the education!! I did not know only exhaust valves get hardened seats?

I guess I got mixed up when I read J's Post

 

I just stopped by the shop and they are actually #8 heads not #5 like he said...I'm thinking he said the wrong thing by mistake...I'm debating whether to let him replace both #7a heads with the #8 heads or just wait and find another #7. He swears the #8 will work fine...

 

Don't go with the 8 heads! You will be SO SORRY! Engine has no go with those! Been there!

 

I told him to hold off and let me check on it...I guess i wont do it...

 

Find another 2-7 head. Those 8's are just too deep.

#8 heads would be fine if you were running flat top pistons, but I doubt that is the case with your rebuild.