The best person to answer your specific question would be EMDSAPMGR on ScreamandFly.com He, Harley Stipp, has a publication on how to mod out the older OMC's "Improving Crossflow Performance 5th Ed". I have a copy and it is great. If yours is a looper I imagine some of this (like shaving the heads) would apply as well.

In general, raising the compression should really not effect the power band much, however it does improve the efficiency and power output.

Here is a good link on the topic: http://www.bridgestonemotorcycle.com/documents/higher_compression6.pdf

Also, grab or borrow a copy of Gordon Blair's book: "Design and Simulation of Two Stroke Engines"

http://books.sae.org/book-r-161

well highe compression is acheived by shaving the heads there for causing a faster stroke thus for more rpms=mph i think this is correct but depends on how much u cut off is what kinda fuel you will have to run and longjevity of your motor comes into play can the crank rods and pistons hold up to the higher compression head gaskets blowing bearing wearing out this all comes into a factor maybe some more guys can chim in on this also hope this helped some but told hp gained varrys

how much more power can be gained by shaving the heads and how much to take off motor is 1990 johnson gt 150