Build up is a 455 Pontiac
88mm turbo w/.96 a/r
stock block filled to water pump holes
4.195 bore pistons r coated top and sides.
heads stock cast iron ported [email protected]
Torker 2 intake ported
850 Carb done by Brent Davis from turbo forums
Piston material makes a difference and the skirt design makes evey bit as much difference in clearance. Turbo pistons typically use a more conventional full skirt design. The newer slipper skirt designs that are popular with the NA crowd do not work well in power adder applications because the way the piston is designed much of the expansion occurs perpindicular to the pin bore. A full skirted piston has much more even expansion that occurs more as radial expansion that allows the piston to expand much more evenly which makes the overall required clearance smaller than the other design when subjected to extreme temperatures. As far as coating/anodizing Diamond recommends subtracting two (.002) thousandths from the listed clearance on the spec sheet which basically makes the moly coating a sacrifitial layer if the piston grows more than expected from some abnormal engine condition. The last Diamonds I used were for a 4.130" bore, the spec sheet called for .0085" which ended up as .0065" allowing for the skirt coating. I would talk to the mfg if there is any question about what the clearance needs to be for your specific application. No body will know more than the people that designed the piston if it is from a mfg that has experience with designing turbo pistons. I hope this helps.