I'm going to hop up my CV25 a bit this winter. It runs props on my hovercraft so I need to keep RPM in the normal range. So far I am going to do a port & polish and a good 3 angle on the valves & seats. I have a 27/30 cam to install because that's what my research indicated.... a custom grind would do little at my RPMs.
heres my other possibilities:
long rod conversion.... really thinking I like that idea. I believe the required pistons also bump the compression ratio a bit due to the flat tops, so the question would be, how much? and would the .060 copper gasket keep me in the range to still use regular gas. the other question is the bores.... to provide the right piston clearance, I will need to hone a couple thou (according to Zack.. I believe him) anyway, some are apparently Nikasil, so that would be out. is there any way to tell without pulling the engine apart (like series/build number)?
Roller rockers.... is there any point in doing this on a low RPM engine?
Roller Lifters.... same?
Spark advance..... what is the stock advance on the 25 and on the 27 (since I might use a 27 cam).
What else? is there something I should consider for an engine that can't turn more than about 3300