Custom Turbo Header

[Turbo_ZA]

I am contemplating a custom 3" exhaust in 316 Stainless (no cat) - from the turbo downpipe onward. The guys are prepared to make me a custom header along the lines of the Lindsey one.
Question is, what is the size of the stock header pipes, and is there any gain/loss to going to larger than stock diameter before the turbo.

[flash968]

wow - is that ever a loaded question - there are a ton of things involved in determining header design and the effects of changes - that isn't a question easily answered, and there are no blanket answers

i would scour the web for exhaust system theory and design, and try to glean some clues from that, entering in the anticipated displacement, length, turbo size, boost level, rev range desired, yada yada

[krystar]

pretty much what flash said.

the geometry and the diameter of the exhaust will affect your turbo spoolup and max boost/cfm/power capabilities. and there is no one answer that's the "best" it's always going to be a tradeoff somewhere.

[Turbo_ZA]

I see the Lindsey unit is a "direct replacement" so presumably they have stuck to the stock diameters - in which case it might be best to do the same. I had a feeling this was probably the way to go unless one was trying to do something really over the top.