Mike, that was on a ST GS-45 with a Macs 2620 header, 8.5cc muffled tuned pipe, an APC 10 x 7 and 5% Omega (with a dash of added Benol) I'm getting 14,300 on the ground with the full length header. Wave-O-Scope says she's unloading to about 15,400 in the air, so we're not talking crazy RPMs here.

The plugs (OS #8 and Fox std. long) weren't obliterated, just "open" far down in the hole... The Phoenix F20 I'm flying it on has a fairly springy engine mount, so I'm guessing it could be a combination of things such as the pipe being too long, vibration, lean, compression, etc... This is my first attempt at running a true pipe, so I expect there to be a learning curve.