I dont know what is this cars problem but ever since rebuilding the head, putting it back on, etc etc it has not been running properly.

A few weeks after getting it running the oil was low, the engine started making a knocking noise at 2500 rpms (and only at 2500), my mechanic cannot figure out why. Everything is how it should be and I'm getting worried.

Charles said it sounded like the catalytic converter going bad. The cat is right off the exhaust manifold and the original did fail 2 years ago and was replaced. So why would this one suddenly fail?

help