We use Darton or Perfect Bore as sleeves for our blocks. The process of fitting the sleeves has been refined over the years to eliminate any sleeve dropping. We us a maximum of 90mm for drag motors and 89mm for road race and 88mm for street duty. Blocks are finished honed and decked. Oil squirters are also installed if needed. We also offer Perfect Bore Nikasil coated liners for the ultimate in bore wear and friction reduction. These bore are coated aluminum liners rather than the standard iron sleeves. Special rings are used with the Nikasil combination. It was thought that the aluminum liners were not as strong as the iron ones. But with extensive testing this has been proven wrong, and more and more race engines are using the Nikasil coated liners.