Exhaust?

ratkc135

Veteran Member
Joined
Feb 21, 2013
Location
Lawson, MO
TDI
2002 Jetta TDI, 2015 Passat
I've searched and don't see a whole lot....

I have my 2002 Jetta TDI with 167K on it. I was under there yesterday putting a hitch on and noticed the muffler is the size of a giant duffel bag. I don't think the original exhaust will probably last another 10+ years so I'm debating putting something new on...preferably that doesn't have a muffler that is so ridiculous. I don't need something fancy or expensive...nor do I think this is a corvette and want a loud exhaust/rumble. Something that will last another 15+ years...improve the flow...no drone or make it so loud inside it's annoying on a road trip.

I initially thought cat-back...but I've read on posts some people regret not doing turbo-back. I can be sold on either option....perhaps it's best to start from turbo and go back? So the stuff in front of cat doesn't go bad and you have to do it anyway at some point?

I'm military and have TX plates...so I don't do any emissions testing...maybe someone in TX can tell me if I will have to do tests eventually....or would deleting CAT be dumb (if I end up in a state where I couldn't pass emissions)? I see so many brands out there I'm looking for some insight from folks that have run different options. Thanks!
 

\/\/0J0

Veteran Member
Joined
Apr 27, 2010
Location
Knoxville, TN
TDI
Sadly, none anymore
2.5" turbo back straight pipe is all you need. You'll never get a vette sound out of a this little 4 cyl turbo diesel. The exhaust does develop somewhat of a note with just a straight pipe and a high flow cat or even a simple resonator in place of the cat will break that up. There is no significant increase in SPL when straight piping (many threads on this if you don't believe me). Buying a downpipe from whitbread or idparts (with or without cat) is a good place to start and your local muffler shop can bend up the rest for cheap

sent from my mobile look-at device
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Until you mod to the point where you're upgrading your turbo there isn't a lot of benefit to changing the exhaust. If you do want to improve flow the downpipe is more of an issue than the muffler. You'll see better response, but not more power, with a new downpipe. With a stock turbo a 2" pipe is more than adequate. A 2" downpipe with no cat and the stock rear exhaust (including that muffler) is a nice setup for a daily driver.

I have a 2.5" exhaust on my wagon with a resonator in place of the cat and a magnaflow muffler. The size of the exhaust is overkill for my stock turbo, but it's left over from when I had a larger turbo on the car. Even with both the resonator and the cat, and with the tail pipe extending beyond the rear bumper to help reduce drone, it does get loud at over 80 MPH. Recently I drove to Detroit with two friends and it was pretty noisy in the rear seat at highway speeds.
 

Fix_Until_Broke

Top Post Dawg
Joined
Aug 8, 2004
Location
Menomonee Falls, Wisconsin, USA
TDI
03 Jetta, 03 TT TDI
I'd keep the stock exhaust and not mess with it. Exhaust on diesels last forever since there's no water (acid) going through them like there is on the gasoline engines. I'd bet that it'll last another 10 years easily, especially in texas where they don't salt the roads.

The only performance thing that you could possibly gain is if the cat is plugged and you might loose a little weight, but as others have already noted, you'll pick up some drone depending on how you do it.

If you're looking for an excuse to modify, we can help you with that as well (see my signature :)) but nothing you've described says that you need or should change anything in my opinion.
 

ratkc135

Veteran Member
Joined
Feb 21, 2013
Location
Lawson, MO
TDI
2002 Jetta TDI, 2015 Passat
Reading the input so far: conclusion is to leave stock stuff there and wait to see how long it lasts. No sense putting money into it when its fine and nothing is to be gained. I thought maybe I'd save some weight...but doesn't appear to be worth that expense either.

Thanks!
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
Reading the input so far: conclusion is to leave stock stuff there and wait to see how long it lasts. No sense putting money into it when its fine and nothing is to be gained. I thought maybe I'd save some weight...but doesn't appear to be worth that expense either.

Thanks!
I'm kinda in the same boat as you BUT as you but I may do the following (most are freebies , minus a little labor) :

1) Hollow out the cat....Maybe even weld a pipe on the inside as a straight through for better flow ( I read if you hollow it out without running a pipe through it , it could flow less due to turbulance inside an empty case (I read that somewhere sounds potentially correct but does anybody here know for a fact if an empty cat case flows less than a straight pipe?)....

I have to keep the look of a cat since we have visual inspections to get annual vehicle stickers....bad since with 242K I m sure the cat has long since died and is just extra weight and restriction)...

Slight weight savings and should be a little freer breathing....maybe even a little extra fuel mileage (I'm on a mileage hunt since I drive many miles long distance).

2) I am thinking of just removing the muffler for the huge weight savings....Ive read they weigh about 20+ lbs....

I think I have heard that a hundred lbs weight saved improves fuel economy 1 percent....not a lot but every little bit helps (to date I've done small things to reduce weight....avus rims not steelies, remove headrests (not drivers tho), seat bottoms etc...(I run a wagon to haul cargo not passengers other than driver), etc....

3) I don't want drone (lots of highway driving) so that is the only reason I am a little paranoid about modding BUT I suppose I could always just put the stock muffler (or lighter aftermarket one) back on even tho the cat may be hollow...

Anyways, just a thought....I am hoping to get some time to experiment.

Andrew
 

Fix_Until_Broke

Top Post Dawg
Joined
Aug 8, 2004
Location
Menomonee Falls, Wisconsin, USA
TDI
03 Jetta, 03 TT TDI
Andrew - In theory, a pipe through the cat will flow better than an expansion/contraction, but practically on a car it won't make any measurable difference.

The muffler is big and heavy. You have several options, but none will make a measurable improvement in fuel economy in my opinion. If you remove the muffler and replace it with a resonator or glasspack kind of thing, make sure you allow some flexibility to change the tip location/position. Every exhaust system is different and wagons can be different than sedans. For me, pointing it at a 45 degree angle to the left (outside) while up under the valance was what worked best to get rid of drone on my car (sedan). If you change the muffler/cat, be prepared to do a little experimenting on tip position/location to manage drone.

If you want to improve your mileage the most for the least $ spent...

1) Get LRR tires when you need to replace them, go taller if you can without going wider. 207/70/15's do a good job of this

2) Use low viscosity engine and transmission oils when it's time to change them. I ran 0w40 in the engine and several different low viscosity oils in the transmission all the way down to ATF. I'd run VW G070 in the transmission.

3) Do a full frontal aero block - grille, lower valances, etc

4) Get a scanaguge or similar device that gives you live/instant MPG feedback

5) Make sure everything is up to date in terms of maintenance, injection timing is in spec (or a bit advanced), cam timing is in spec (or a bit advanced)

6) Slow down where you can - A few MPH make a big difference in MPG's, but a very insignificant difference in actual door to door time. A couple stop lights on either end can wipe out a 5 MPH speed difference on a couple hour drive pretty easily. Rarely will a few minutes make or break anything.

7) Consider a tune that advances timing - rarely will you get the MPG advantage sufficient to offset the cost.
 

20IndigoBlue02

Top Post Dawg
Joined
Aug 22, 2001
Location
Was North NJ, now SoCal
TDI
2002 Golf TDI-- deceased
keep the cat on. If you want to replace the car, get a diesel specific cat. Diesel smells are annoying.

after the cat, chop off the muffler and weld on a straight pipe. THis is referred to as the "mufflerectomy"
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
I have two MKIV cars, park them in the same garage. One has a cat, one doesn't. Can't say that I can tell a difference in exhaust smell. If the car is tuned and running properly you probably won't smell anything other than sweet diesel exhaust.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
This is the first diesel I've had with a cat on it....my diesel pick up and van are too old for cats and don't smell bad to me....
 

bobbiemartin

Veteran Member
Joined
Jul 16, 2012
Location
Jacksonville, FL
TDI
2010 Tiguan TDI 4Motion, Jeep Grand Cherokee 3.0 CRD
Exhaust design is probably a bit more complicated than just willie nillie changing components. You might want to read this. While it's written around atmospheric V8s, the info is worthwhile.

If you are looking for cheap and easy mods, an hour or so with a suitable piece of rebar (or equal) and a hammer to break up the inside of the cat may yield a slight improvement. Not that I'll admit to any experience with this but you can hear the turbo at idle (at the exhaust pipe) so maybe it does do something. I would suggest a respirator should you decide to embark on such a dastardly endeavor. Is a hollowed out cat akin to a pressure wave tuning box? Is having one beneficial on a turbocharged engine? I really can't say, but I would think it doesn't hurt anything either. On a near stock engine, I would suggest such a modified exhaust is more than adequate. Couple that with an 11mm pump and some 520 nozzles and you have a nice driving TDI for not a lot of money.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
In thinking of a cat as a restriction, I'm not sure why BUT I had a 1987 Ford van that relatively quickly lost all its power...PLUS it has somehow gained a strange wheezy sound.

I took it around to a couple shops, and they all seemed to "know" (or maybe suspect) a collapsed cat...

With that a friend of mine and I cut the cat off and the guts literally poured out ( not sure to this day how that even happened)...

The van was so low on power that pedal to the metal would not hardly cause reasonable acceleration much less enough exhaust to blow the stuff out.

After we poured out the cat and he welded things back up, my van was good as new.

Granted, at this point, I am no where near that level of miserable performance with my Jetta, but a preemptive strike would prevent me from being stranded somewhere or limping along at 30 MPH or so because of a collapsed or clogged cat.

It would be interesting tho to somehow put a pressure gauge in the exhaust upstream of the cat to see before and after back pressure changes arising from 1) gutting the cat and 2) removing the muffler...

Has anybody here actually measured back pressure with a gauge before and after?
 

Fix_Until_Broke

Top Post Dawg
Joined
Aug 8, 2004
Location
Menomonee Falls, Wisconsin, USA
TDI
03 Jetta, 03 TT TDI
Exhaust design is probably a bit more complicated than just willie nillie changing components. You might want to read this. While it's written around atmospheric V8s, the info is worthwhile.

If you are looking for cheap and easy mods, an hour or so with a suitable piece of rebar (or equal) and a hammer to break up the inside of the cat may yield a slight improvement. Not that I'll admit to any experience with this but you can hear the turbo at idle (at the exhaust pipe) so maybe it does do something. I would suggest a respirator should you decide to embark on such a dastardly endeavor. Is a hollowed out cat akin to a pressure wave tuning box? Is having one beneficial on a turbocharged engine? I really can't say, but I would think it doesn't hurt anything either. On a near stock engine, I would suggest such a modified exhaust is more than adequate. Couple that with an 11mm pump and some 520 nozzles and you have a nice driving TDI for not a lot of money.
That's a good article - technical enough to have value, but simple enough to understand (unlike a lot of magazine articles).

Thanks!
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
I posted this above but it bears repeating. The bigger restriction in the stock downpipe is the flex, not the CAT. The inside of the flex is about the diameter of a quarter. In addition, the bend coming off the turbo is far from optimal.

Having repeated that, I'll also repeat that you'll not see a significant benefit from an improved exhaust until your mod levels are beyond a tune and injectors. When my car was in the 180 HP range changing to a 2.5" exhaust got me 8 HP. On a more mildly tuned car the increase would be far less.
 
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