3" Downpipe + 4" Exhaust in A4 Jetta

[Fix_Until_Broke]

Great ideas, thanks. I am still thinking of a 2.5" stainless DP to the CAT, a 3.5" cat, I'm betting I could come out of the cat, go to 3" or even back to 2.5", and then within a foot or so sleeve clamp on aluminum pipe for the rest of the run. I really like that idea. If I go 2.5" I probably won't use a muffler at all: My wagon is quiet without one, only starts a bit of a drone at 90+.

I know my 2.5" hits the bolt heads for the rear bar if it's not adjusted just right, and I had to swap the bolts so the heads are on the top to reduce the amount of space they take up. The bar's coming out of the car anyway so that won't be a problem, and maybe I can run a 3" all the way back.

Doesn't your 2?5? turbo have a 3" V band flange on it already? A 3" DP is really not all that hard to make - just need to put the flex in the CAT tunnel instead of over the steering rack.

Someday I'll take the EMP measurements on various downpipes so we can stop all this speculation - maybe this spring/summer when it's warmer out

Even if you have to put a dent in the bend going over the axle (or squeeze the cross beam together a little bit) would be better than running 2.5 all the way in my opinion.

 

[IndigoBlueWagon]

Yes, but, I have two issues with using a 3" from the turbo. First, I don't think there's room to flare the pipe from 2.5 (or 2.25 with the 2056) to 3" and make a smooth 90 degree turn. One thing I've learned with the exhausts we're now making is the smooth turn coming out of the turbo has some significant benefits. Second, I think the flex pipe location is important. I know you've had some issues, but consider the type of use and engine movement the race car has, even with stiffer mounts. A flex pipe further down doesn't allow as much movement without tugging on mounts and welds.

I'm going to review the rules, maybe I can get a diesel exemption for the CAT, since it's not tested in my state. If I can pass state inspection without one I think I can make an argument that I don't need one for class rules. If so I'll go with a Magnaflow Race muffler only. And I'm going to look into what it might take to get a 3" pipe over the axle.

 

[Scott02]

Peter, 3" should go over the axle without too much BS.

We already know that 4" will go over it !

 

[IndigoBlueWagon]

I might try one of these.

 

[DbLog]

Peter,
2.5"-> 3"-> flex pipe-> 3.5" spun cat-> 3" back-> over axle- out-> works. That flange you had made is awesome. Here's a pict of the current downpipe. Old parts and new. Could be prettier but the Michigan winters like to cause havoc under the car. You should put that dump on there FTW!!

Yes, but, I have two issues with using a 3" from the turbo. First, I don't think there's room to flare the pipe from 2.5 (or 2.25 with the 2056) to 3" and make a smooth 90 degree turn. One thing I've learned with the exhausts we're now making is the smooth turn coming out of the turbo has some significant benefits. Second, I think the flex pipe location is important. I know you've had some issues, but consider the type of use and engine movement the race car has, even with stiffer mounts. A flex pipe further down doesn't allow as much movement without tugging on mounts and welds.

I'm going to review the rules, maybe I can get a diesel exemption for the CAT, since it's not tested in my state. If I can pass state inspection without one I think I can make an argument that I don't need one for class rules. If so I'll go with a Magnaflow Race muffler only. And I'm going to look into what it might take to get a 3" pipe over the axle.

 

[TDIJetta99]

that dump is awesome! You could use a solenoid and an adjustable boost activated switch to open it under high boost conditions.. Have a nice quiet muffler on it so it's silent while cruising, then all hell brake loose when you stand on it..

 

[milehighassassin]

Getting a 3" over the rear axle is no problem at all. The 1.8T crowd has done this many times, mass produced and all.

The dumps are sweet but most I have seen have long term reliability issues.

 

[boosted alh]

I might try one of these.

that thing is never going to be in stock, i was going to get one last year but they said they dont expect to be producing it anymore, so you are better off making one yourself

 

[IndigoBlueWagon]

I'm probably going to make one that I switch manually. I'll use the muffler on the street and the dump on the track. And I want the dump to go straight, not make a 90 degree turn.

 

[TDIJetta99]

How about this one? I haven't used one from jcwhitney at all, but it might be worth a shot considering how cheap it is


edit.. or one of these from Summit.. with one of these..

 

[IndigoBlueWagon]

Nice but too small. I talked to chill this morning and he agreed that a 3" shouldn't be a problem over the axle. I may try doing a 3" from the turbo back with a 3.5" or 4" spun cat and a short 3" Magnaflow race muffler.

 

[TDIJetta99]

they make those motorized ones in 3" too... I've installed a few on street/strip cars..

 

[Fix_Until_Broke]

I finally downloaded/uploaded some pictures of my latest downpipe modification that I did around the 1st of the year and figured that I'd post them up finally. Like I had mentioned before - not the prettiest work possible, but I'm all about functionality

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[milehighassassin]

Very NICE!!!

 

[Mach1]

Nothing wrong with that..Highly functional...

 

[00JettaTDI]

I cut the muffler off of my 2000 Jetta, and now I'm looking to go to a 3" straight pipe exhaust. I have a couple of questions. Could I use the stock flange and/or piping from the turbo to where the CAT was or should I get a 2.5" DP, and adapt to 3"?

 

[Fix_Until_Broke]

Given your larger turbo, I think you'd probably benefit more with a larger downpipe than using the stock one. I've started collecting data to quantify the differences, but it's slow going.

Depends on your budget ($200-$600 for a 2.5" DP) + whatever you will do for your 3" "Cat Back". I know you said straight pipe and it's neat for a couple weeks, but after that it gets pretty old (at least it did for me). So you'll likely add the $ for a muffler as well

If you don't mind doing some fabrication you can make you own.

Hope that helps...

 

[00JettaTDI]

Thanks for the info. I'm thinking of going with a 2.5" DP to a 3" pipe. I'm confident I can fab whatever needs to be fabbed as far as cutting and welding. What kind of impact does the placement of the 2.5"-3" joint have?

 

[milehighassassin]

In all honesty it seems silly to do a 3" catback and a 2.5" downpipe. Opposite would be better, but 3" all the way would be best. I am looking at building a 3" complete system. I am unsure if I can handle the downpipe but am going to give it a go. I will probably get a reducer that is port matched and then expand to 2.5" to the flexafter the flex it will be 3". I am not sure if the flex will be 2.5 or 3. 2.5 is cheaper.

 

[00JettaTDI]

I've got a 2.5" DP, and need to do the exhaust anyway. I'd prefer to do 3" all the way as well, but considering the cost and finding a 3" DP I'll just use the 2.5" I have.

 

[Fix_Until_Broke]

Bump - edited 1st post again.

I added the 4040XL Aeroturbine muffler back in where the OEM cat goes to get rid of some last high load drones when pulling the trailer and couple minor resonances at various RPM's.

Dare I say it's OEM quiet now.... I'd have to go drive a stock TDI and see for sure, but it's much better - particularly outside the car.

No rattles/vibrations/etc with the additional muffler. I think the full 8" flex section and the 3" swivel joint at the turbo outlet make it much less prone to vibrate.

 

[mootster16]

I have my car still all stock but using a 96 stroker intake with all stock exshaust with gutted cat and 4 inch straight pipe from akle back sound about the same as yours does but i love the sound. Work great to put my friends kids to sleep lol

 

[Fix_Until_Broke]

I've had some subtle engine vibrations that I have not been able to track down and I think I found the source of some of it.

These are the "mid mount" hangers right behind where the OEM coupling behind the CAT is.

Needless to say, they were not "hanging" much anymore. I welded the OEM pins on the 4" pipe and used these hangers originally. Over the years (going on 4 years now) the rubber deterioriated and the pins were suppported by them sitting on the bottom of the rubber on the cross member instead of hanging from the top.

I didn't get a picture of what I replaced it with though it's much beafier and of a different design. I'll try and get a picture of it next time I'm under the car.

It's one of those things that you don't notice until you fix it and say - "wow, that's a lot quieter now" because it happens so gradually.

 

[Fix_Until_Broke]

So I had the car up on the hoist the other day and took some pictures of the mid mount fix.

I took a heavy duty hanger mount similar to the one shown on the right

I cut it in half and put one half on each side like this

The center part fits right down inside the cross member. I welded a couple little tabs to the cross member to keep the pipe centered like shown below

I gave it a quick coat of paint after I welded it up

The pipe just sets there on the rubber mounts - it can rock forward/back a little on the rubber mount and is constrained side/side with the tabs. Gravity holds it down.

So far so good for the last ~500 miles or so - much smoother, but not completely smooth yet. Still a bit rough at lower RPM's (1100-1600 RPM). Might need to check out the dogbone mount next (again).