fly cut pistons

[zeiss150]

Has anyone ever fly cut their pistons? Is it done just to lower compression? Or does it have some kind of HP benifit? I would love to get an answer on this one guys.

Thanks Matt-

[mdbrandy]

I'm not much of an engine builder (yet), but I am under the impression that fly cutting the pistons is done for valve clearance, so you don't have the valves impacting the pistons if you have inadequate clearance. Decreasing compression ratio is a side effect of this.

FWIW.

[Phred]

You get an "A" Mark. Fly cutting pistons gets its name from the type of tooling, or cutter used to mill reliefs in the tops of pistons. When aftermarket cams are used that have higher lift, and longer duration, they sometimes can come in contact with the pistons. This usually happens from ten degrees before, to ten degrees after TDC. Most race engine builders will temporarily install the pistons, then set the head on with no valves. Then with a long center punch made out of an old valve, drop it down through the valve guide to make a small mark on the piston top. Then with the pistons disassembled, and mounted in a special holding fixture, the cuts are made in the pistons, centered on the marks made with the punch. Then final checked again to assure that they have the required clearence. Safe clearence for valve to pistons is generally .060 for the intake and .090 for the exhaust. This operation is sometimes referred to as Bridgeport cutting for valve to piston clearence, because a universal head Bridgeport milling machine is commonly used.

Phred

[frank13]

Hey zeiss150, in your other thread about this phred was the member I had in mind when I said some of the other members that actually build Engines. You can also get new pistons ordered with valve reliefs already cut out of the piston. I'm glad you got your answer. Sorry I diddn't get that part of the question. But from what I understand from other members and read from phreds post he is the right man to have got the answers from. :devious: