Just wanted some info on this for a project of mine (not an evolution or mitsubishi for that matter) and thought it may get alot more input over here since their seems to be alot more knowledgeable people in this forum than others.

lets say i have an 81mm std. bore size from the factory, and i take it out to 84.5mm bore. if i have the head ported what would be the pros and cons to leaving the combustion chamber the same 81mm circumfrence as opposed to having them open it up to 84.5mm besides the fact it will have a higher comp leaving it as is and a lower comp machining it out to 84.5mm. or is it even possible to leave it at 81mm without running into trouble when going with that much bigger of a bore?

 

your bore size on the head stock is somewhere near 83mm..so it is not to much to make it bigger. It would benefit from the bigger chamber, so you don't have the material in the bore creating basically more quench and leaving it open to detonation. But, also consider your CC chamber size when purchasing the piston for compression numbers. As you will be making it larger then stock.

 

I respectfully disagree. Quench zone is your friend and shouldn't be taken out unless you need the cc's.