Engine Noise

[67Camaro RS/SS 350]

The instructions say to adjust them using a feeler gauge, like a solid lifter. I thought doing it running was a hydraulic thing? Before the head swap, the engine made 18" at idle and that was with a 76cc chamber. Will the vacuum change if the compression ratio changes?

[Jim Nilsen]

The instructions say to adjust them using a feeler gauge, like a solid lifter. I thought doing it running was a hydraulic thing? Before the head swap, the engine made 18" at idle and that was with a 76cc chamber. Will the vacuum change if the compression ratio changes?

I would do them according to the instructions they put out now. My lifters were on the car when they first came out and I know they have made small revisions over time. It would seem that if they were all the way out with lash like a solid they wouldn't have room to pump up or down, but that was then and this is now 27 yrs later.

I too had 76cc heads and mostly had 21 in. of vacuum at idle.

Vacuum is more effected by the cam duration and overlap than by compression.