[Alan Roehrich]

Al, you can run that spring. I know a few who have tried and do not like the results. I prefer a regular style spring and a tool steel retainer.

How much you might gain by reducing open pressure depends on what cam core you run and what your open pressure is now. We've tried taking spring out, it has not worked for us. You can have too much open pressure, for a cast core cam, that's anything above 525 pounds. You'll get twist, and you'll lose lift. I'd run a steel core cam in a ZL-1. Too many RPM and too much lift for a cast core, in my opinion. Tim will be doing a steel core cam for ours, I talked to him about it the other day. I'd have it in the new 396 if the core would work at 0.520" lift.

You shouldn't have to mill the 401 head a ton to make spec for a 69 ZL-1, since the spec is for an open chamber. You could do a valve job, put the valves and a spark plug in it, then mill it in steps, 0.0" to maybe 0.020" angle, and creep up on it. Then you might have to re-drill, but you'll certainly have to spot face, and correct the intake face.