Do precups affect compression ratio?

[mpascino]

I've been reading a few posts that suggest they do, however I don't see how they could have that much of an effect. Any ideas?

[Dieselboy]

IIRC, grape CC'ed his combustion chambers with turbo precups and found they would yield something like 19.7:1.

[G. Gearloose]

Uhm, because thats where most the air goes...

[mpascino]

I was refering to the fact that the two differnt precups volume wise don't appear significantly different. Is there really air in there? tongue.gif

[grape]

1 cc is alot when you have a 39 cc combustion chamber and 750 cc cylinder.