Help with compession ratio

[redjmp]

Well I finally got my vortec heads today! #12558059. I think these are the same castings as the coveted 062's but with 1.84" intakes instead of 1.94".
I think they can be fitted with 2.02's if I want.
170 cc runners and 64cc combustion chambers like the '98 350 heads.
These were only used in '97 305 trucks and were the precursor to the 12558062 introduced the next year.
However they are not the same vortec heads as used on later model 305's with 58cc chambers and therefore installing them on my 84 305 with stock pistons will lower the compression.
The question is by how much and what are my options for obtaining around 9.5 to 1 which is what most mercruisers run.

 

[John_S]

Re: Help with compession ratio

Probably the question to ask, before buying the heads. Anyway...

Become familiar with one of the many compression ratio calculators on the web, such as this one: http://www.wheelspin.net/calc/calc2.html

If your pistons are recessed, you will have to find out the cc's. Also need to pick a head gasket for compressed thickness and diameter.

FYI: when I ran the numbers on a SBC 350 with all stock parts, it does not equal the advertised 9.4:1. It was closer to 9:1.


Given a 305 and larger chamber, if you do have recessed pistons, it will be a challenge to get the ratio you are looking for.

Options: Shave heads, deck block, thin head gaskets, different pistons. One or more, depending on where you are at at what you will settle for.