I have a 1969 camaro with a 454, all exhaust pipes on long tube thermal coated headers are reading temp. out between 200 to 400 degrees (using laser light temp reader) except cylinder #6, it is staying around 600 to 700 at 2,500 RPM's. it is cherrying or glowing header.

The 454 is stock oval port motor with 510 or so hyd. lunati cam. I have changed carb 3 times used a holley 600, 750, and 850 all vac. sec. and no change, have checked for vaccum leaks, and none found, backed valves off till they are chattering to make sure not to tight.

Have changed intake also, and changed plugs.
Put air pressure into cyl. to make sure no leak in exh. or intake valve, none found.

I am out of ideas has anyone came across this issue before?

What is ideal exh. temp. on 454 chevy