I am building my 455 for the W-30. Our goal was 10.0:1 compression. We got to 9.8 and I am happy with that. My question is not important to my outcome but wondering how much .2 - .5 compression will affect a 455 engine. I know there are many variables to this that I am not posting but just looking for thoughts.

I come from the single cylinder off road MX sport and .5 can be very significant but we are only talking 525 lbs for the bike and rider.

 

Your looking at around 3% per every 1 of compression in this range. As you get higher in the compression ranges, the percentage increase is less.

 

I don't think you're going to feel this in the seat of your pants. It really depends on the complete package and your intended use. The variables start from there.

You know there are a lot of them... variables I mean.