I stayed with 9.5 Andrews 21 cams and it pulls like a John Deer ,Makes 41 to46 mpg runs on 87 octane fuel which is all that is available in a lot of places were i ride .

 

A great tuner once told me that you can make just as much hp and tq with a very dependable 9.50:1 compression ratio. Build starting with cams and find the right person to do the heads and then a good person to tune the bike. Reliable 90+ hp all day long. My heads are next on my list having Autotune.

 

A great tuner once told me that you can make just as much hp and tq with a very dependable 9.50:1 compression ratio. Build starting with cams and find the right person to do the heads and then a good person to tune the bike. Reliable 90+ hp all day long. My heads are next on my list having Autotune. He got right at a 100 hp with my old 80" EVO with cams and SE heads running a D&D pipe.

 

With out MCR's my stock heads with 103 flat tops are theoretically supposed to produce 10.0:1 compression. However , whenever I read about compression there's always a multitude of reasons why theoretically compression never happens , especially with folks that have ACR's or MCR's put in and it's always some number less, and folks wind up using thinner gaskets, machining, or both.

So if I assume that the theoretically compression of 10.0:1 will not happen with my combo of parts, and I don't mill heads and don't use thinner gaskets.....what about a different piston. I also have a set of SE 103 forged pistons with a theoretically compression of 10.5:1. If we assume, that the theoretically compression of 10.5:1 won't happen either , but keep the goal of trying to achieve 10.0:1 I'm thinking considering the added volume of the MCR's, and wonder if a slightly thicker head gasket (opposite direction from the folks who are trying to add 0.25 more compression) I can probably wind up very close to the targeted 10.0:1 goal. AND what if I miss it, and wind up at 10.25:1, whats the consequence...will it hurt my low RPM range (doubtful) or is it a limitation for max power at higher RPM's (likely)?

I know what to do once I assemble and compression test and figure out my actual compression ratio...but I want to try to get close as possible before I assemble. I guess I am trying to understand what the tolerance should be 10.0:1 plus or minus what .....0.25, 0.125, etc. If I get 10.25:1 I would probally run with it.