What motor to go with?

Spend 47 more dollars and get these
http://www.summitracing.com/parts/UEM-KB167-040/

with 68cc chambers they should give around 9.1, though if you mill down to 64cc you'll get about 9.5 and so on...

or spend another 20 over those and get these and have around 10.4 comp w/68cc or 10.1 w/72cc roughly

http://www.summitracing.com/parts/UEM-KB399-030/

they dont show a .040 over but im sure they make one.