Speedmaster Small block porting tips and results Part 1

I doubt they could keep the TIR to under .050 if they just used the guide as a pilot if I'm getting your drift.

I have never liked a live pilot cutting system. I prefer a dead pilot with a ball drive tool head.

The ball drive takes up any misalignment you might have, up to a point.

? Are you referring to .050 TIR on a seat that was precut and THEN installed in the head, .050 TIR is a Football field of runout.