milling the bottom of cylinders

[carl74344]

I have seen this a few times now. why would you do this? is it something I want to do? is for oil flow?

[HawgRyder]

Extra clearance for a longer stroke crank?
Or maybe the owner changed rod type and needed more space to swing them?
Bob

[carl74344]

so for a stock motor no real value. would it help oil flow? it would be easy to do.

[911pcars]

A modification to minimize air flow restriction as piston moves toward BDC. Supposedly saves/gains X HP in high revving engines to extract max. power. YMMV.

Sherwood

[Walt Fricke]

This is often called "mooning" the cylinders. Goes along with profiling or otherwise narrowing and smoothing the tops of the main bearing webs. Race motors only, really, where cost/benefit holds much less sway.