Inkubus

Hey all,

So I need a new exhaust system (you may have seen my old thread). I decided since the one I got is cheap and hangs too low and blah blah I'd get a new one.

Some point in the future I wanna do kswap w/ turbo...probably k24a2 with a k20 head. Right now I have your standard D17A2 in my 02 Civic EX.

All I can find when searching for exhaust systems on that year is 2.5", sometimes 2.25". I read online though about 3" exhaust pipes (and downpipe) for turbo. But I can't even find a 3" exhaust system lol.

Is 2.5" gonna be enough? Will it be okay, in the future with a turbo engine, to have 3" downpipe going to a 2.5"? All help is of course appreciated.

ezone

Visit an exhaust shop. Most good ones can custom bend just about anything you desire.

Inkubus

My current pipes are 2.5". If I go get a hack job done on it by the local guys it's probably gonna fall apart in a year..

ezone

Desire a bunch of 3" stainless?

Inkubus

That's what I wanna know, actually. If 3" is practical for a turbo kswap or if 2.5" is fine, or perhaps if 2.25" is better.

ezone

IMO one wants as little restriction after the turbo as possible, so the largest pipe dia. as practical ------ along with figuring how much increased volume a boosted engine will have to expel at redline and under full boost.

On a NA engine some tuning can be done with the header pipe lengths and diameters. Not so (much) when a turbo is involved, as the turbo is a both a restriction and a power adder.
In some states the turbo could be considered the silencing device (muffler) as well (used to be... some rules may have changed since I learned this) so one could go with straight pipe after the turbo, no muffler at all..(check your local regs)


IIRC, a basic rule of thumb was......
If you run 15 PSI boost that's going to produce about double the exhaust volume over when the engine was NA.
If you run 7.5 PSI that's about 50% increase in volume.

Remember to figure for this when doing your calculations in the link below.

Check this article:
http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/



tl;dr, 3" is probably plenty big LOL
HTH