I am building a small block 406 for my 69 Camaro. 400 block bored .30 over with 5.7 rods and standard steel crank. I have K.B. flat top pistons. My question is the heads, I was told that I had to stay with large chamber heads(76cc) to keep the compression down. I am considering running the late model vortec head L31 with 64cc chambers. Can anyone tell me what the compression ratio will be with this combo, and can steam vents be drilled for the 400 like the earlier heads?
Thanks for any info

Go to classicalpontiac.com in the restoration section. There is a compression ratio program you can use online.

Larry

Make it clickable: http://www.classicalpontiac.com

Thanks, Great site.

Assuming nominal gasket thickness, you'll be in the high 11's almost 12 or so depending on the valve relifs etc. I've got the same combo you do, 406, Speed pro flat tops, and ported GM 461X castings (64CC). My compression comes in right at 11.8 or so. The other thing to consider is the cam you are going to use. I have a somewhat agressive 292H cam, which has lots of duration, which means the piston is already on it's way up when the valves shut. So in reality even though static compression would be fierce 11.8:1, the dynamic compression is really somewhere in the 9's. Therefore I do not have detonation problems and can run premium pump gas. If you use a smaller cam with short duration for torque, the the dynamic compression starts getting closer to the static compression, and that's when you get into dangerous territory regarding high compression and detonation. Hope this helps...

[This message has been edited by Shawn (edited 11-18-99).]

The gasket thickness is .039 and the cam I have installed is a Crower 288HDP. Intake is 288º with .497 lift. Exhaust is 296º with .504 lift. This is a street engine and am concerned with detonation and overheating. According to compression formula, I should be around 11.25. This may be to high.

My question is how did you know without knowing the pistion ratio couldn't he get 12:1 pistons or he could he 8.5:1 not sure how you got your ratings without knowing this.