Sounds too big, we use 26 x 10's on the 3 Evo 80's we run. They are on full canister set ups too. Never checked rpm, but on a 27 x 10 I would think you are in the low 5's (depends on brands, some prop manufacturers have a strange idea of 10" pitch)
Hi Dave thanks for the reply I have it in a giant scale thunderbolt it's got a stock wraparound exhaust it's doing 5700 rpm do you think I should drop down a little on size thanks Neil