Zane's 71 327 Ram Horn - restrictive?

[burnin oil]

You dont see it often on street motors but maybe a valve spring harmonic is occuring and limiting RPM. This is normally on a full race motor. Do your valve springs have a rotator inside? This would look like another valve spring inside but made out of a flat wire instead of spring wire. You could try to pull those out and see if the RPMs change. If that is the problem I would be very suspect of the valve springs and would have them replaced with another set.

Another thought is a cam wiping a lobe. I had one that started to wipe an exhaust lobe and that really made the motor run like crap. Before it got really bad it would basically not exhaust that cylinder but was still trying to fill it and run. Lot of back pressure there.