2.5" or 3" exhaust, thats the question.

**juamin** · 10-06-08, 11:43

Well i want to put a new exhaust in my car, with only one muffler at the rear.

Should I go for a 3" exhaust or for a 2.5" ?
im plannig to change the chip, maybe in a few months a t3/t4.

there are any pictures of a 3" and a 2.5 " exhaust?

thanks .

**wrinx** · 10-06-08, 12:21

I think 2.5 is the average size....and what I plan to fit.

wrinx

**Brul(tm)** · 10-06-08, 12:21

Originally Posted by juamin

there are any pictures of a 3" and a 2.5 " exhaust?

The rear silencer

2.5" plumbing

I left this behind

Greetings,
Marc

**juamin** · 10-06-08, 12:26

Originally Posted by Brul(tm)

The rear silencer

I left this behind

Greetings,
Marc

thanks marc, but you didnt replace the cats , did you?
I think im going to replace from the turbo to the rear part. .

**Brul(tm)** · 10-06-08, 12:29

Originally Posted by juamin

thanks marc, but you didnt replace the cats , did you?
I think im going to replace from the turbo to the rear part. .

That's what I did, the cats are still there. Only the very first one after the first bent is gone and the down pipe sligthly adjusted. The original is already quite good. This is quite loud and has a very deep dark sound

Greetings,
Marc

**juamin** · 10-06-08, 12:32

Originally Posted by Brul(tm)

That's what I did also

The cats are still there.
This is quit loud and has a very deep dark sound

Greetings,
Marc

jej i just care about performance, don`t care about the sound, but if it sounds dark and deep ill be very happy.
so ill reach a better performance with a 2.5" than with a 3" ?

**Brul(tm)** · 10-06-08, 12:35

Originally Posted by juamin

so ill reach a better performance with a 2.5" than with a 3" ?

That all depent on your plans with the engine. If you stick with a performance chip and no serious rebuilding of the engine, I think you'll be save with 2.5". Otherwise 3"might be the better option.

Greetings,
Marc

**juamin** · 10-06-08, 12:37

Originally Posted by Brul(tm)

That all depent on your plans with the engine. If you stick with a performance chip and no serious rebuilding of the engine, I think you'll be save with 2.5". Otherwise 3"might be the better option.

Greetings,
Marc

great, thanks marc so ill go for the 2.5" then

**Brul(tm)** · 10-06-08, 12:41

Originally Posted by juamin

great, thanks marc so ill go for the 2.5" then

I am no expert on this matter

I only read something on the internet about this subject. Just wait for a reaction from the guys who did some serious tunning one their engines. They can speak out of their own experience

Greetings,
Marc

**juamin** · 10-06-08, 12:52

Originally Posted by Brul(tm)

I am no expert on this matter

I only read something on the internet about this subject. Just wait for a reaction from the guys who did some serious tunning one their engines. They can speak out of their own experience

Greetings,
Marc

jeje dont worry, i wont go runing now and do it, ill wait for the opinion of the guys with serious engine tuning.

**q4fatboy** · 10-06-08, 14:25

I run a 2.5" on mine, no Cats and just a single rear box. It is louder than standard but not over the top. I run Hybrid Turbo & uprated chip and it has really put an edge on the performance.

**AlfaJack** · 10-06-08, 15:38

What performance are you ultimately looking for?
The 2.5 on mine seems fine

**juamin** · 10-06-08, 15:52

Originally Posted by AlfaJack

What performance are you ultimately looking for?
The 2.5 on mine seems fine

ohh its difficult to answer now that je but by now, i have the std chip and turbo.
Im going to change the exhaust, then new chip.
and when i get bored, ill put the T3/T4 hybrid .
Maybe, in a future (a year or something) ill put forged pistons. But for now, beucause of what ive read here 2.5" will be Ok.

**Evodelta** · 10-06-08, 21:47

Exhaust size is linked with power output - more power demands a bigger diameter exhaust and on a turbo engine bigger is better, some drag cars run with only a very short pipe which exits at the front. Non turbo engines are different, you have to carefully match exhaust dia with power, go too big and lose power.
I de-catted mine and went for 3" with only one silencer at the rear, the power output went up so much the clutch then slipped.

Problems expected with bigger exhaust and de-cat:

Noise. SS is thin therefore more noisy, less cats and silencers add to this, it can be a PITA on the motorway.

Clearance issues if badly made, although bigger will always hang down further.

De-catting isn't very good for the environment and illegal in many places.

Turbo failure. The small turbo tends to lean against the back pressure of the restrictive cat and exhaust, take this away and it will spin up lovely, so much so It will eventually collapse. A good excuse to trade up to something a little bigger.

**wrinx** · 10-06-08, 21:51

What would the power difference between 2.5 and 3.0?

wrinx

**juamin** · 10-06-08, 21:53

Originally Posted by wrinx

What would the power difference between 2.5 and 3.0?

wrinx

jeje wrinx i was about to ask the same question! jeje

**jimnielsen** · 10-06-08, 22:48

what do you guys think of this? Its a CHEAP T3/T4 turbo... its ebay # is

360058642313

jimn~

**wrinx** · 11-06-08, 07:39

http://cgi.ebay.co.uk/ws/eBayISAPI.d...3%2B%26fvi%3D1

Ridiculously cheap, which says a lot for me...but not a lot to lose either

wrinx

**AlfaJack** · 11-06-08, 08:18

Personally I wouldn't buy that. I think in the turbo world you get what you pay for. Any weak link in the unit will show itself pretty soon due to the speed they work at.

**jimnielsen** · 11-06-08, 09:49

even cheaper with an internal wastegate.. isnt this about 180 British pounds??

http://cgi.ebay.com.au/MonstA-T3-T4-...QQcmdZViewItem

**#84** · 11-06-08, 10:30

Normally you should go for 3" if you aim a bit over 300 hp. I have ~320 hp and 2,5" with the two standard cats in parallell.

What is best to do is to use the CO-measuring output, just next to the lambda probe, connect a hose from it (first steel pipe, then hose because of the heat) and have a pressure gauge in the cockpit. If the pressure is below 0,1 bar it is ok. If it reaches 0,3 bar it is really bad. I would not let the exhuast back pressure go over 0,2 bar.

**Evodelta** · 11-06-08, 12:26

Originally Posted by wrinx

What would the power difference between 2.5 and 3.0?

wrinx

It depends on whether the 2.5" was restricting the flow in the first place or not, which then depends on the output of the engine.

What I am trying to point out is that you can't go too big with a turbo engine, but you can be too small.

**Evodelta** · 11-06-08, 12:33

Originally Posted by jimnielsen

what do you guys think of this? Its a CHEAP T3/T4 turbo... its ebay # is

360058642313

jimn~

It looks like it fell out of a Christmas cracker.

Guys, don't buy your tuning parts from Ebay, it's the last place to go. The only time you can buy something on there is if you are already knowledgeable on the subject of whatever is for sale, then you will know for certain whether it is a bargain or not. If not leave it there, there is usually a good reason something is cheap or somebody is getting rid of it.

**wrinx** · 11-06-08, 21:54

Originally Posted by Evodelta

It depends on whether the 2.5" was restricting the flow in the first place or not, which then depends on the output of the engine.

What I am trying to point out is that you can't go too big with a turbo engine, but you can be too small.

Thanks...I'm only looking for 300bhp (eventually!!!) but it looks like 3" might be the way to go.

wrinx

**wrinx** · 11-06-08, 21:55

Originally Posted by Evodelta

It looks like it fell out of a Christmas cracker.

Guys, don't buy your tuning parts from Ebay, it's the last place to go. The only time you can buy something on there is if you are already knowledgeable on the subject of whatever is for sale, then you will know for certain whether it is a bargain or not. If not leave it there, there is usually a good reason something is cheap or somebody is getting rid of it.

...lets leave my camshaft out of this

wrinx