As someone who builds a ton of SB2.2 engines both for circle track and drag race I agree with edvancedengine something doesn't sound logical, first off 108 mm is 4.251 what block other than the new billet 4.5 bore spacing will handle that bore size. second 18.0-1 is diesel range. once you get above 15.5-1 we have found almost no gains in torque. we have several engines out there at 15.0-1 with a 400 shot and no problems. with a 1.045 c.d. and a .300 deep int pocket there is no room to run N20,the piston will fail at the int pocket.Bill