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Originally Posted by JC
PV=nRT. Volume stays constant so when you increase temperature you increase pressure. Using Bernoulli's equation pressure and velocity and inversely proportional. So when you increase temperature, velocity should go down?
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V= infinity... It is not a closed system, so PV=nRT is not directly aplicable without significant modification. It is a really a fluid/gas dynamics problem.
And exhaust gas starts contracting pretty much the second it stops combusting(Heat source). There is no additional heat in the headers/uppipe, so anything you can do to retain the existing heat will minimize contraction, and maintain velocity to the turbo. There is even a theory that pipe diamater should decrease in the uppipe to increase velocity as the gasses enter the turbo. The gotcha with this is that it produces increased back pressure in the headers which can diminish power.
After the turbo, it is all about minimizing back pressure, velocity is not terribly important. There is actually something to be said for not having the larger piping start until after the cat, so the tendency will be for the again expanding gasses to exit via the lower pressure higher volume piping, but on a turbo, the increased back pressure at the turbo probably negates this.