Stingrr

What's the chamber volume of the stock heads on a '67 Vette with a 327-350 ... 58 cc, or 64 cc? I thought it was the latter, but replacement pistons from TRW (#L2166NF) indicate that the stock compression ratio of 11 to 1 is attained with 58 cc heads. Are the TRW pistons exact copies of the stock pistons - if not, can the stock pistons still be bought new? GMPP doesn't list them on their web site ...

d1_bradley

I'm like you, I thought it was 64 also. See this site, they do too.
http://www.chevytalk.com/tech/engine/SBC_Heads.html

SWCDuke

The OEM heads should be nominally 64 cc. There were several design iterations of the factory
forged pistons between '62 at '66. I suspect the TRW pistons represent the last design.

My Federal Mogul Performance Parts catalog specifies a 10.23 CR with the L2166F pistons
and the 64cc 461 heads, but you should read all the info on how this was computed.

Actual CR will be a function of piston deck clearance, head chanber volume and
the head gasket thickness, and catalog has a
good section on making the measurements and calculations to detemine the actual CR.

The actual CR of the L-79 from the factory probably averaged about 10.5 and the cylinder
variation on any given engine could be as high as half a point.

You might want to consider some flat top pistons to limit the CR to about 10:1 depending
on the above referenced issues. This should allow you to consume pump premium
without significant detonation.

Duke

Stingrr

Bradly - thanks for the URL! That is indeed quite informative. Duke, I'm planning to have my 327-350 rebuilt using World Products Sportsman II heads (I don't trust the local shops to do the job right of putting hardened seats into the original heads), and I've been playing with various combo's of 64 and 72 cc chambers and TRW pistons of various designs. Thanks for the tip on the variability of the CR and the measurements used, btw. I'd like to try and keep the compression ratio from dipping too much, as I LOVE the crisp sound and idle characteristics of a high-compression SB. I won't be driving the car all that much, and will make liberal use of octane boosters with 93 octane, or 100 octane racing gas, as well as peeling back the timing if need be. Summit Racing's tech specs also list 10.23 for the L2166F pistons; they don't list a standard bore flattop piston, but the 30-over piston (L2165F30) has a CR of only 9.07 with 64-cc heads. The 60-over piston (L2165F60) has a CR of 9.18. I'm afraid that if I go too low with the CR, I'll lose the crisp sound and idle, even if ping would be minimized. Decisions, decisions ...

d1_bradley

Also remember that you can run a high static compression ratio with a SERIOUS cam and the effective cylinder pressures will trick it into thinking the CR is lower than it is. You can talk the some of the cam manufactures about this and they can get you the grind you need. I have a 331" small block with 11 to 1 on 92 octane and it doesn't ping. Thumps pretty good at idle too. Its in a light car (street rod) so its fine on the street.