After installing 3.0L valves in my 2.5L heads, along with quite a bit of deshrouding, I ended up with between 47.0 and 47.3cc. Accounting for the headgasket and all, that equates to a 10.43-10.49 compression ratio.
Somehow I recall a 11.2 CR if the 2.5L heads are installed untouched. That would be 43.2cc
The 2002 3L heads untouched were 49.0 cc, yielding a 10.14 CR.
While I ended up flowing about the same as the siamesed 3L heads with my porting 2.5L heads, fully ported 3L heads would have further gains.
3L heads are the easiest option.
