[quote=thomas.hood;1643883]A few questions for Kumaran:
4. I've never read (besides magazine advertorials) any convincing reasons why ceramic coating (or wrapping the exhaust) is a good idea. Even on 'cost-no-object' supercars* this is not done (AFAIK
), so forgive my cynicism.
wrapping and coating:
The idea comes from the knowledge that hotter gasses are less dense. Hot internal temps into a cold manifold will cause the gases to contract and become more dense. With this increase in density, and the same presure behind it, It will have to exit slower.
Now to understand a little more, remember 2 stroke engine have an expansion chanber to carry exhaust gasses away. they make the gas move faster by reducing density in a different way, IE: expanding volume.
But as you note, on a 2 stoke, the expansion chamber is not a wide cone to the atmosphere. That means that this is a balance between exhaust velosity and backpressure in order to tune your power curve.
So on a 4 stroke engine with SS or iron headers ( no not wrap TI) , you can wrap them to change the internal speed of the exhaust in the headers by preventing the increase in density slightly. And thus getting more power on the top end. It also prevents heat soak on the intake side, but thats more of an added benifit, and not the reasson for doing it usually.
Without a dyno, Its very hard to get it right, so its best to let the deep pockets play with the wrap untill they find out what works, because going into it blindly is not always going to yield power gains.
FWIW- wrapping stock headers on most stock bikes would get 2-3 hp on the top end. WE always went with full Ti exhaust on my race bikes, so I've never wrapped mine, only friends and bikes I built for people.