Hello all, I have a 400ex, It has been bored to a 440. I was wondering, it is getting close to time for a top end rebuild, what is the highest compression that I could run. I will be able to burn 110 sunoco purple race fuel. Thanks!

 

As far as the fuel your burning; about 14 to 1. But detonation depends on a lot more than static compression.

 

If you go over 12:1, at 89mm, the head studs become an issue. You can get a stud kit, and you'll thank yourself in the long run, if you get them. The stock studs can pull and lead to head gasket leaks or worse, pulled studs.