Steel exhaust pipes, headers or extractors have a large surface area and quickly pass heat to the air that flows around them. This heats up the air in the engine bay reducing its density. The engine then draws the hotter air in through it’s intake system. This heated air is less dense than cooler air and contains fewer oxygen molecules and the car loses some power. This excess heat can also melt ignition leads, wires and hoses.
Another lesser known fact is that as the exhaust gas leaves the cylinder head and starts to dissipate heat through the exhaust pipe, it starts to contract and lose velocity. If the exhaust gas could keep its heat level then the exhaust gas wouldn’t slow down. The inertia of the exhaust gas leaving the exhaust port of the head actually helps to draw more exhaust gas from the chamber and draws in the intake mixture. As more exhaust gas has been drawn out of the chamber the intake mixture doesn’t have to mix with the remains of the exhaust gas. The result is better scavenging of exhaust gas from the chamber, more intake mixture in the chamber and a better burn and potentially more power.
Racers some years ago tried wrapping their exhaust pipes in fibreglass tape to insulate the exhaust pipes and found the benefits mentioned above.
So, can this wrap damage exhaust pipes. In short, the answer is yes and no. It is possible that racers such as NASCAR in the USA or Endurance racers may experience overheated exhausts pipes due to the insulating properties of wrapped extractors or headers and this can cause cracking or fatigue, but in 99% applications, header or exhaust wrap will NOT damage exhaust pipes.
All mild steel exhaust pipes will eventually rust and the best way to extend the life of your exhaust pipes is to coat them first with a high temp exhaust paint or a silicone based paint.
Unlike other wrap products, Kool Wrap exhaust tapes are more flexible than other wraps and don’t require wetting prior to wrapping.
You will notice some smoking from the wrap after first start up but this will disappear over time.
There are no hard and fast rules about recommended overlap, however we say that a minimum overlap of around 5mm (1/4”) is fine although you will often have to have a greater overlap on the inside of bends.