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There are four oil-return ducts in the big-block's lifter valley. For the Top Stock engine, the front three are blocked off, while the rearmost duct is screened off, and a small trough below directs returning oil to the back of the engine. This is done to prevent the oil from dripping onto the crankshaft, thereby causing windage. The blocking plates and trough were handmade from .040-inch aluminum, while the plates and screen were affixed with Devcon epoxy.