# 4" exhaust on a vrt with 700+



## 98rzvr6 (Nov 12, 2005)

Hey guys i see some people running a 4 inch downpipe and some guys even run a 4 inch exhaust all the way till the rear axle so my question is it really worth it and will it benefit me that much? I plan on running right over a tiny bit 700 and my concern is trying to fit a 4inch downpipe in a 98 jetta vrt? is it pretty hard or can it be easily achievable? I know it will definitely help with spool up and less backpressure for the turbo which will help. Thanks for your all help


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## nothing-leaves-stock (Mar 1, 2005)

if your good or have a good fab'r a 4'' DP can fit. but 4'' over the rear axle most likely won't.


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## 98rzvr6 (Nov 12, 2005)

Ive never made one nor am i that great at fabbing stuff up but im gonna try my best lol, wish me luck


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## prometheus_ (Oct 6, 2009)

98rzvr6 said:


> Ive never made one nor am i that great at fabbing stuff up but im gonna try my best lol, wish me luck


can possibly do 4" to a dump valve, and then a reduced 3" from the dump back


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## TBT-Syncro (Apr 28, 2001)

the other option is dual 2.5. its going to be heavier, but it'll probably be easier to fit


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## therealvrt (Jul 21, 2004)

My 4 incher (hehe) is ovalized and we notched the rear axle slightly. Doesnt seem to have affected handling ( rear beam twist) and it does not rub!!!
DP is 3.5 inch btw


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## j.Connor (Mar 7, 2002)

Despite you saying that notching the rear beam showed no noticeable effect it sounds REALLY sketchy.:screwy:


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## V-TEC this!!! (May 4, 2003)

My friend notched the rear beam on his '02 GTI due to the fact that his 3" exhaust would rub when he had ppl in the back. He took the car to the track went over the rumble strip and the rear beam bent right where it was cut. 

If I had to notch the rear beam I would weld in plates where the notch was done to beef it up.


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## therealvrt (Jul 21, 2004)

It is reinforced
Duh


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## pimS (Jan 7, 2009)

TBT-Syncro said:


> the other option is dual 2.5. its going to be heavier, but it'll probably be easier to fit


2x 2.5inch = the same surface as a 3inch pipe


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## TBT-Syncro (Apr 28, 2001)

pimS said:


> 2x 2.5inch = the same surface as a 3inch pipe


you should re-do your math, if thats the result you get. 

dual 2.5 inch is about 38% bigger than a 3inch, and about 28% less than a 4inch. 4 inch is almost double the volume section of a 3 inch.

2 inch 12.566
2.5 inch 19.635
3 inch 28.274
4 inch 50.265

:beer:


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## pimS (Jan 7, 2009)

Yes you're right

3inch exh. = around 45 square cm's
2 x 2.5 inch = around 64 square cm's


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## need_a_VR6 (May 19, 1999)

My 3.5 clears fine with some massaging to the floor and a stock beam. I could see a 4" fitting.


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## 98rzvr6 (Nov 12, 2005)

Well is it really worth it to go through the hassle of getting a 4 inch dp? Will it help me that much or is it not worth it?


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## TBT-Syncro (Apr 28, 2001)

pimS said:


> Yes you're right


it happens around once a month. lol

:laugh:


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## simple_man (Jun 18, 2006)

need_a_VR6 said:


> My 3.5 clears fine with some massaging to the floor and a stock beam. I could see a 4" fitting.


3inch DP and 3.5 inch catback here. I am getting exhaust touching the chassis when going over bumps or reversing uphill.
So, it does fit, but takes a bit of making around to get it right. I feel that getting that 4 inch fitted maybe a bit of work of art. Not every shop will do it. Especially if you want not just a pipe but a resonator and muffler added to it.

BWT, that 2300RPM drone is killing me. Anyone worked out perfect fix for it on 3.5 inch system?


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## V-dubbulyuh (Nov 13, 2005)

need_a_VR6 said:


> My 3.5 clears fine



Mine too but then again it terminates prior to the rear axle. Could not be bothered with the additional fab work required.


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## need_a_VR6 (May 19, 1999)

Mine is all the way back. Kurtis @ MBS did amazing job.


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## GTijoejoe (Oct 6, 2001)

Normally you don't want to go big to small....the smaller will still be the choak point.... run a 3.5" and call it a day....4" is huge to fit on a vw 

my $.02


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## zwogti (Jan 11, 2004)

If I were you, I would think more about the tranmission than the 4'' pipe pushing over 700 on a 3.L vr6, but we had and still have people making 700HP on 3'' downpipe and exhaust, so I don't see why you need a 4'' exhaust. if you want to go big, I don't think you need anything bigger than a 3.5 exhaust.


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## therealvrt (Jul 21, 2004)

zwogti said:


> If I were you, I would think more about the tranmission than the 4'' pipe pushing over 700 on a 3.L vr6, but we had and still have people making 700HP on 3'' downpipe and exhaust, so I don't see why you need a 4'' exhaust. if you want to go big, I don't think you need anything bigger than a 3.5 exhaust.


 This could be true but evolution has to take place. If nobody tries it how will we know. When i first turboed my car 268s were wayyyy too big now 10 years later i run 288s which were too big two years ago.


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## zwogti (Jan 11, 2004)

.therealvrt said:


> This could be true but evolution has to take place. If nobody tries it how will we know. When i first turboed my car 268s were wayyyy too big now 10 years later i run 288s which were too big two years ago.


 
^^^^^^ I'm sure I'm making more power than you, I'm on stock head, running on low boost, 3'' downpipe/exhaust, 125K miles original vr6 cam, Turbonetics regular bearings turbo, not on race fuel. I think 700hp on a vr6 is a lot when you have to deal with the torque that the engine will make and start to brake the gears, if you want to go over the 700hp, than add a set of cams, 3.5 downpipe/exhaust will be a good add on.


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## TBT-Syncro (Apr 28, 2001)

i've seen dynos of cars picking up over 100hp from 500 to600+ from going 3" to 4". different platform, but 6 cylinder turbo motors none the less.


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## simple_man (Jun 18, 2006)

I can say that going from OEM 2.5inch to muffled and resonated 3.5inch on turbo VR6 made a very noticeable difference without a dyno :thumbup: 
That is running only 14-15PSI


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## lugnuts (Jul 26, 2001)

The easy answer is to run the car on a dyno with the exhaust connected, and then do a run with an open DP. 

You could do a 4" DP and then you will have a set-up that will make tons of power 
with an open DP. But you could transition that into a 3" or 3.5" and possibly still be better off, because of the DP giving the exhaust some room to expand while it is still hot.


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## 98rzvr6 (Nov 12, 2005)

Hmm Thanks a lot Kevin, never really looked at it that way but it does make sense.


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## sleepin gti (Jan 21, 2011)

i run 4" strait pipe most of the cruising season, sometimes i throw the muffler on but very rarely.. it does have good spool i generally see full spool around 3500-3800. I have considered running a 3.5" for the possible power gains but to be completely honest i love the sound of 4" strait pipe way too much to do that 








































as you can see it is v-banded right there for the muffler, only takes 3 mins to swap it out :thumbup:









have a good one guys :thumbup:


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## V-dubbulyuh (Nov 13, 2005)

sleepin gti said:


> i run 4" strait pipe


Impressive that you go that to fit, my 3.5" is tight in some areas.


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## sleepin gti (Jan 21, 2011)

V-dubbulyuh said:


> Impressive that you go that to fit, my 3.5" is tight in some areas.


haha well as much as id like to take credit for that i cant. the origional owner did it or had it done i believe. but i agree that is some damn good fab work.


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