decadude

hey guys i have a 2.5" custom exhaust was told 3" downpipe makes a huge differnce with the K03 and even more noticable with the K04. was told that i would have to redue the Exhaust to a 3" straight out is this true or can i use 3" down pipe with an adaptor ??? thanks

johnAWD

Sure, but it won't be the best for flow. And you'll have to do some flange voodoo on the 3" end, probably. Something like a 2.5" flange on the 3" pipe to mate up to the 2.5" catback.

Regarding flow, consider of a 1" garden hose feeding a 3/4" garden hose. More velocity with some restriction. I'm thinking that 3" exhaust plumbing is way overkill for these small turbo'ed motors. A 2.5" should be more than sufficient until you are flowing enough around 400 wheel hp.

The generic rule of thumb is that more exhaust flow is better for turbocharged motors. Relieving backpressure is a good thing, but the backpressure is introduced by the turbine & turbine housing, most likely not the exhaust plumbing. Using larger diameter exhaust plumbing will indeed allow it to be more free flowing, but the exhaust plumbing isn't going to be the bottleneck.

I'm currently flowing in excess of 700 crank HP (6 cylinder supra motor, 3" downpipe into 3" apex N1 catback) worth of exhaust flow through 3" plumbing. A local DSM pal of mine was flowing about 350 hp worth of turbo, plus 75 hp worth of nitrous, through 2.5" pressbent plumbing. The car was into the mid 11s at 5800 ft ASL.

IMHO.

Sorry - I tend to get long winded at times...

xr4tic

I used header collector reducer that goes from 3" to 2.5", then had a flex joint on that connected the reducer to the rest of the exhaust.

DP:
<a href="http://johnbaas.dyndns.org/2point0/exhaust_2.jpg"><img src="http://johnbaas.dyndns.org/2point0/exhaust_2_lo.jpg"></a>

Reducer:
<a href="http://johnbaas.dyndns.org/2point0/exhaust_1.jpg"><img src="http://johnbaas.dyndns.org/2point0/exhaust_1_lo.jpg"></a>
If you're exhaust is like mine, and has the inlet reduced to fit the stock DP, cut it off.

Flex joint:
<a href="http://johnbaas.dyndns.org/2point0/exhaust_3.jpg"><img src="http://johnbaas.dyndns.org/2point0/exhaust_3_lo.jpg"></a>
I'm eventually going to have the assembly welded up, but the clamps will do for now.

I got the reducer and header flange from Jeg's

Saturnine

Im kinda going to have the same setup as yours.. I just need a muffler with a 2.5" inlet that has nice tips.. People have sugested Sebring, remus mufflers.. but i cant find info on them or who even has them Tia

-John-

decadude

with the turbo did u notice more power etc....

thanks

xr4tic

I have a scorpion exhaust from the downpipe back, it's all 2.5"

xr4tic

I have 2.0 with a T3/T4 turbo, I don't realy have a "before" to compare to

SameerP

Im getting confused...i have a PES T28 kit with the 2.25 borla, so im looking to upgrade. One part tells me 2.5 is the best compromise, another part suggests 3.0" is best...what should i do?

Also, was the reducer a common part?

TIA John!

Cheers,
Sameer

xr4tic

there's enough room, but you'll want to use a DTS and/or snub mount to help keep it from moving around too much. Mine clears the DTS with ease.

With a T28, I'd go with a 3" However, I have heard that the 3" DP w/o cat could cause overboosting problems on the PES kit, which may or may not have been fixed.

I'm also only running one O2 sensor, I'm not sure if that will cause problems or not

The DP consists of:
<a href="http://www.jcwhitney.com/item.jhtml?ITEMID=4069&BQ=jcw2">3" Mandrel U-bend from JCWhitney</a> - $27.49
<a href="http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=13028&prmenbr=361">Hooker 3-bolt Flange Reducer (3" to 3.5")</a> - $23.99
<a href="http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=24652&prmenbr=361">Hooker 3" collector ring kit</a> - $18.99
Stock DP flange and O2 sensor bung

The reducer and flange ring come in packages of 2, so I still have one of each laying around. Let me know if you're interested in it.....

You'll also need a flex joint, I already had 2.5" one laying around.

One of these days, I'd like to get the whole thing done up in stainless steel, but I need to take care of some other things first....

SameerP

so those three items together would make a aluminized 3" downpipe which i could then mate to any exhaust. What benefit does one get from a 3" DP running to a 2.75 or 2.5" exhaust? Milltek is 2.75 past the DP, everyone else is only 2.5". Is there any benefit to having the exhaust restriction downstream?

Second, ive always wanted to ask, i assume you have another daily driver around since your car has been out of commission so long?

I already have the APR snub mount and the AWE DTS so i guess this is another option to spending the big bucks for an off the shelf system.

Cheers,
Sameer