I talked to my friend who owns the speedshop yesterday and he had the same experiance as Jmac, cylinderwall thickness is very important! When he competed in dragrace in the beginning of 2000 his team struggled with braking cylinders-walls. They had a Volvo B230 16V engine that was pushed to the limits, the cylinderwalls were 3,5mm but they still broke due to massive detonation. They had over 1000hp and ran a impressive time of 7,96 in 2003, this was the European record for four cylinder cars back then. They also tried sleeves but ended up casting new billet blocks.

Marcus