I am thinking about building a 350 engine with a dynamic comp. of 9.5.I have a 350 that I have .030 over speed pro pistons with .125 domes and a summit cam and I get a dynamic comp. of 9.5.Does this seem to high for pump gas. Let me know. thanks proge

Imho, yes, unless you use a big cam and bleed off some compression..

NOT good -- way too high..

Shoot for about 8 to 1 Eff. CR. unless you are running aluminum heads.

Go over to Pat Kelley's great Effective Compression Ratio site that you get to through his sig. and READ it at least three times!!

pdq67

Yes, thats very high for pump gas as far as dynamic goes. Are you sure you don't mean static? Dynamic is where you figure in the cam timing to the comp. ratio. Because to get a 9.5 dynamic ratio with a small dome .030 over piston, you must be running a really small cam with a small combustion chamber. Please give the entire combo so we can figure this out.

My 383's compression ratio is 10.47:1 runs on 91 all day with 34 degrees of advance... no sign of ping or knock....

I m thinking of building.71 chev. .030,64cc camel heads, .125 dome speed pro +3.8 dome,sumitt cam 292 intake and exh,488 lift,47abdc.I think it was on the kb pistons that I did the effective comp.Static comp. would be 10.8 and dynamic was 9.5

Are your pistons flat top?

Am I correct that youve got a 3.8cc dome piston? That makes 11.6:1 compression with the 64cc cylinder head(And a zero decked block with about a .040 thick gasket). Thats a lot of compression. One thing I see is that the intake valve closing angle you have provided looks to be the .050 number. When calculating dynamic compression ratio, you need to use the advertised intake valve closing angle for your calculation for it to come out right.

You will need roughly an 80 degree advertised intake valve closing angle to end up with a dynamic compression ratio of 8:1. But even with DCR falling in line, if the cylinders fill half descent, you will have a very hard time getting by on 93 octance with better than 11.5:1 compression and cylinder heads with 40 year old combustion chambers(read not very efficient fast burning chambers). You would be much better with about 10:1 static compression....10.5:1 at best, and that would take a flat top piston with valve releifs that total about 6.5c to 8cc. Also, zero deck the block and use a .039 inch thick gasket and you get good quench. That will help you out a LOT in your quench to build a pump gas friendly motor. You keep those dome pistons in there and your asking for trouble.

I have decided to run flat top speed pro pistons with 2 valve reliefs.This will lower the comp.I am still tinking about the heads.I was going to run the camel heads.the guys say they are old school heads.What other heads would you recomend that dont cost a fortune? thanks philr