asmall

I am starting this thread to talk about header technology and construction. I know there is a whole bunch of information regarding the science of long tube vs short tube headers, the pulse transit time, cooling, velocities, etc. If you want to add any of that here, feel free. But the issue I am concerned with is heat retention, material type, and performance. I am going to stick to long tubes since I am talking about material.

First, the basics. The purpose of the header is to carry the exhaust from the port to the outside of the car. From the port the gas comes out hot (very hot!!), flows down the tube, and mixes with other ports' gasses, where it then makes its way down the tailpie. Once the fuel stops burning, the gas starts cooling. As the gas cools, it's pressure drops. As the pressure drops, the velocity drops. The result is that the gasses don't flow into the collecter as fast and help extract gasses from other tubes.

Onto the question at hand... Material. You've got your mild steel, relatively cheap, conducts and radites heat fairly well, and tends to rust. Then you have your Stainless Steel, more expensive, and from what I understand, holds heat much better than mild steel. Also resists corrosion, and look snazzy. Next is your coated header, usually made of mild steel. Because of it's coating it won't rust (on the outside), holds heat well, and costs more.

More heat retention is better, but I have heard that the coated mild steel tends to get weakened by the heating and cooling. As a result, it's life is shorted. Has anyone ever experienced a cracked header? What do you know about them?

Cheers