Does it hurt airflow to go from a 3in aussie DP to a 2.5" exhaust? I mean it must be better than the restrictive CAT on the DP already. But i heard it is bad to switch diameters of the pipe, any answers?

bigal

like art once said, cats are for lonley people, not turbo cars!
the best exhaust on a 3s is no exhaust.
anytime you step down in piping size, it will become a restriction..
will it absolutly KILL your power?? no, but it will make a diffrence.

OK...is it possible to get a 2.5" DP?

bigal

yes, KO racing makes a nice 2.5" DP

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Yea i remember that KO provided a valid argument why 2.5" is better than 3" on sub 300 hp level, doesnt that contradict the whole "no exhaust is the best exhaust for turbo cars" argument?

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that was before the dyno tests were run and proved otherwise

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they were just trying to push their product. on a turbo car, bigger is better.

the only benefit i can see to a 2.5in is that it it will probably be less likely to give you boost creep issues.

All depends on which downpipe you get. I was shocked to hear the stories of the 3"XS downpipe with the grinding and reinforcing of the whole part. And the boostcreep people get when not taking the metal grinder to the inside.

All the people that have boostcreep had a XS DP not an Aussie. So I know which one I want, even if it means its 100 dollars/euros more expensive.

But like presure said. Going back from 3" to 2.5" can cost you a few horses, but I doubt you will really notice it since stock piping is 2.25" The CAT is really restrictive. Without it it allows the turbo to spool up really fast. Plus with aftermarket DP you save about 25lbs of weight.

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Not all the people, actually i read up on mr2oc and gt4oc that aussie had boostcreep issues too but obviously not because of wastegate clerance but because they had 3" past the DP also. I have read about aussie cracking even when properly braced.

Im not saying that xs = aussie, but its $200 more expensive, the xs DP i got was nicely welded, when i put the turbo flange gasket over the dp there was no apparent need for grinding, friendly welder welded it up for $40, VHT coating $7, i new gasket $9. Came out to under $150 and the only downside is the wall thickness. I know there are people who ran xs for well over a year with no problems. I need to put my cat back one every year for smog so monitoring the condition of xsdp is not an issue to me.

But by all means any dp other than xs is will require less preparation, less maintenance and probably longer lifetime. I do not recommend using xs dp. And i hate SSAC so called "customer support" or lack thereof.