I own an 99 400ex and ride primarly MX. I was wandering what the power gain and in what spots of the powerband, mid, top, low. I was thinking of the wiseco 10:1 or 11:1 piston. Thanks for the help?

 

I don't know this for a fact, but from dealing with V-8 engines, you can expect a 5-10% power increase through the entire RPM range by raising the compression ratio 1 point (9:1-10:1, 10:1-11:1, etc). You'll usually have to run higher than 93 octane pump gas if you want to go to 11:1 compression in a V-8 also.

 

I rebuilt a 1986 200X engine with a 12-1 piston and high lift cam from web cam. I found there was an increase throughout the rpm range (I think due to the increased air flow), but I saw a particularly large increase in the low end power (due to higher compression ratio). If you go the route of higher compression ratios, the low end increase is great but be prepared to buy higher octane fuel. 12-1 ratios normally require 102 or better depending on the motor, valves, etc. Otherwise, you could and probably will damage the engine with too low of octane causing pre-detonation. I have been running turbo blue (110 octane) and have had very good results. Turbo blue runs about 3 - 4 bucks a gallon depending on where you buy it. Wiseco should be able to tell you over the phone what octane minimum will be required for your motor for different compression ratio pistons. I personally think that a high compression piston is the "most bang for your buck" method of increasing low end torque as long as you don't mind buying the fuel.