I have a 86 250R, just rebuilt to a 265 with the spacer between cylinder and case, mildly ported cylinder, pipe, reeds, A/S carb, etc. and a coolhead. I had a 21cc dome in the motor before it was rebuilt. Long story short, (2 month's worth) the shop used the same 21cc dome. The new motor started with about 115lb's of compression and now broke in, has 148lb's. I would like to be up around 170-175, anybody know what dome size I would need? 19cc, 20cc? I called the shop, they said 1 cc equals about 10-15lb's, and that 150lb's is about max compression I should run without using 110 cotane. No they don't sell fuel. That response didn't make sense, my stock motor with cool head had 155lb's, it ran fine on 91 or 93 when I didn't want to get race fuel. If there full of crap on the 150lb's of compression needing 110 cotane, do I trust the 1cc equals 10-15lb's?