It was dropping off at 6200, the customer didn't want to run it higher. It may have been lifter pump up, the preload was about 3/4 turn. I thought about putting heavy duty c-clips in the lifters and running less preload but we didn't have the time.

The drop off might have been the engine going out of tune as far as intake/cam/headers it might have been an RPM they didn't like. I think that is more likely as it sounded good, no misfiring. We have run the stock Magnum lifters at higher RPM on the IMCA V-6.

The dual plane Performer RPM seems to be more prone "going in and out of tune" when compared to a single plane. I had an M-1 ready to test but again didn't have the time.

What has been you experience with an upper RPM limit with the stock hydraulic roller lifters?