I am trying to get the compression down on my 1972 350 SBO and was considering a .051 head gasket. Right now my CR is just under 10:1 (9.89:1 to be exact) with a .040 HG and would like to be around 9.5-9.6:1.

Any feedback as far as:

1. the performance and durability of a .051 HG?
2: and/or engine modification needed if any. Will they bolt right on?

Here are my bottom end spec:
-bore 4.087
-stroke 3.385
-7a heads 64cc (cc'd at the machine shop to confirm 64cc)
-pistons -3cc valve relief
-deck height .011
-head gasket .040

Thanks

 

What's wrong with 9.9 to 1? Add some race gas if needed. If you don't drive it much, the price of race gas is trivial. Do you have hardened valve seats? If not, you will want to use some lead or substitute. You could use a 25% race gas mix and achieve both goals, octane and seat protection. If you really want to get a thicker gasket, the only one I know of is the expensive Cometic but you will probably need the .060" thick one. If you get them from an Olds vendor, they can advise you further.

 

Hi run,

9.5:1 fits my engine model the best. Your right the cost is minor for race fuel but what a PITA that would be.

As for the valve seats, it is my understanding that year head has induction hardened valve seats from the factory.

 

Yes in 72 the heads would have hardned seats. All the 7a heads did.

According to my math, a .051 HG should drop you to about 9.6:1

http://www.csgnetwork.com/compcalc.html

 

Thanks for the input Red

 

FWIW it seems to me you would be trading static compression ratio for a total deck clearance/quench distance that has moved well past the "ideal" .040-.045 range. You are starting out @ .051 and would end up over .060 w/ thicker gasket. I don't see where you are gaining anything. If octane requirement/preignition resistance is your aim, I still don't think you are going to improve much if any. I think all you end up with is slightly softer performance. Seems like a fair amount of work to perform for probably no gain. Hopefully some people who really know what they are talking about will chime in, this is just my opinion.

 

Less quench may not be a good thing. A set of #8 or any BBO heads will also drop the compression too. The RPM heads and intake would go nicely with your 350, just need an electric fuel pump.