how thick i the layer of coating?
wouldnt coating it on the inside alter the diameter of the piping and can have an effect on how the header performs?

 

Kid, no. its very thin of a coating and isn't enough to effect that much of a performance in any car. Maybe if you were measuring in 1000th tolerances in an F1 car.. but its not anything you, nor I, nor a dyno would ever notice. jet hot... thumbs up here.

 

Isn't the stock pipe a dual (tube within a tube) affair? How does the coating work with this kind of arrangement? I thought that's why we have two tubes. Does anyone know the answer?