I built my own manifolds a while ago using thick buttweld fittings...now pipe inner diameter is quite large so i thought flow would be good. I've only just gotten car running (NC V8), jump in it cold, start up and drive...get 400mt down the road, pop bonnet and headers are glowing...im trying my hardest to not get the engine on boost. Now, internals are standard, boost is at 6psi, turbo is a t-70 with a 1.0 exhaust housing, and engine is running a stock n/a tune, was just driving to carwash 500mt away and trying not to get on boost.... any ideas?

very retarded ignition timing or lean fuel ratios will make manifolds glow.

Yep check timing..Check cat as well..