Originally Posted by
Matty
Yeah from what I found as a general rule is that boost comes in earlier, on an equal length manifold, but this also relies on the pipe sizes being correct. From the pictures I have seen of the tubular manifolds available they are either 32mm bore or 35mm bore pipe (could be wrong through?). Ideally you dont want to go for something around the exhaust valve size, as restriction isn't an issue like an NA engine, as the turbine is the biggest restriction. I'm going to use 29mm bore pipe for the one I am making, this should make the turbo spool quicker, and increase the mid range torque.
On some of the engines I have made exhausts for they haven't gained Peak HP as such, but they have made the same power with less boost, and broadened the power accross a larger Rev range. My aim is not big numbers, but a torquey engine with a broad power band. As the T25 .49 exhaust housings seem to be non existent I am hoping that it will help spool a .64 rear end.
It would be good to see what Simpsons came up with!