my friend had an lt1 383 built at the local speedshop. it has used lots of oil since day 1,.....like 1-2 qts a week. the motor has an hrc 4340 crank, compstar 6'' rods, and ross forged flat tops. we pulled the heads off & noticed right away the pistons rocked a little excessive in the bores. the pistons mic 4.025 and the bores are 4.031-4.0315, and round within .0007. the top ring gap was .022. 2nd ring was about .023.
the motor gets TONS of blow by in the oil. the cylinder walls look fine.
what should the piston to wall be? it leaked down 70%. and im pretty sure the heads and gaskets were sealing. any ideas?
.004-.006" piston to wall is normal for an all forged piston depending on bore size.. LIke mentioned above, check to see if rings were put on upside down.
__________________ 2000 SS M6 black SLP package, spec stage 2 clutch, RAM billet steel flywheel, BMR sub frames, Lakewood LCA, Random Tech. Adj torque arm,
How many miles is on the motor? .007 is loose but is definitly not unheard of. Most of the latest forged pistons are designed to be able to run the tighter clearances such as .003 to .004 to keep noise tamed. .007 shouldnt cause a ring seal problem in a fresh motor, given that it had the proper bore finish for the ring package and that it was honed with a torque plate. It probably wont thrive to 100,000 miles but should'nt be short lived either if everything was right in the beginning.
If it is round without a torque plate, it probably wasn't honed round with a torque plate. Take some pictures of some of the cylinders and maybe a couple pistons, and post them up. That might tell more of the story.
piston to wall clearance? 
