My 518 low deck motor with 440-1 CNC ported by MCH made 775 HP on Oregon pump gas with 10.8 to 1 compression and absolutely no quench to speak of.(at 4300 FT above sea level also, DTS dyno straight up no fudging ) The pistons have a 22 CC dish because the motor originally had a set of ported 906 iron heads on it I should replace the pistons to a set of reverse dome with some quench, I'm sure there is some power there It is way easir to turn up the squeeze HP than it is to start with to much compression Big motors(C.I.) make a lot of power without a bunch of compression I'd shoot for 10.5 to 1 or lower