from my understanding it's the other way around.

From the engine manifolds, there is a downpipe (from the top of the engine to the bottom of the car) then into the cat and so on....

And most exhaust systems are JUST cat-back while others also include the downpipe and are thus downpipe-back.

as far as Stebro goes, I have no idea. I know APR includes the downpipe.

And I'm by no means an expert and could be wrong, but this is the impression I have from this board.

Mark P

I learn more every day

So would a cat-back system include everything back of the cat? (including downpipe)

and a downpipe-back system including everything back of the downpipe (excluding downpipe)

I knew the downpipe was sometimes include and sometimes not, so when I heard the term downpipe-back, I assumed this included the downpipe. But if the above is correct this thinking was incorrect.

everyone's so helpfull :o)

Stebro is downpipe back. People seem confused on the difference. The cat is connected to the turbo. The downpipe is connected to the cat, and runs down to a slip joint that connects it to the middle pipe that you can see underneath the car up towards the front. Stebro and several other aftermarket exhausts go from the slip joint back, not replacing the downpipe. Some systems are now going from the cat (replacing the downpipe) back.

There are several advantages/disadvantages to replacing the downpipe. First, it is a pain in the ass to remove (slip joint back exhausts take about 15 min to install). Second, the factory downpipe provides some backpressure to help low end torque. This is evidenced by dyno runs after replacing it. Audi designed the 1.8T for a torque plateau from 1800-4500 rpm, and there is a reason they designed the exhaust like they did. If you replace the downpipe with a big sewer pipe, some of the low end slam of the 1.8T will dissapear. However, if you are racing and need power at 5000-up, you probably want to replace the downpipe as it does open up the exhaust at higher rpm's. I would guess that cars equipped with the Neuspeed exhaust do lose some low end (perhaps compensated a bit by their chip), or it feels a little mushy.

In the race to say their parts provide x horsepower and the others suck, you'll start seeing parts that really don't work well for everyday street cars but are more race oriented, such as exhausts.

Dan Stebro told it was full catback and John H. told me it was not, BUT he gave me reasons why downpipe back only is BETTER for the turbo.
Heh now you have changed the whole thread of my
post....guess I'll have to repost tomorrow. ;)
I'm glad you got all your terms straight now =)
Once your 2000 A4 comes in(SOON!!!) so much of the stuff you read here will finaly make so much sense. I know before I had mine, stuff like wastegastes and coilovers made no sense to me...
That has all changed. Also seeing so many different model/year Audis at the Glen helped shed light on many other things too.
HOW SOON TILL '00?

-Jenner
'99.5 1.8T QMS Spoiler/Garrett/Mintex/17" MM Spiders(in route!)

I guess I will just have to remail him. But no matter which is it I would like to get your exhaust! Reply to my last email!

-Jenner
'99.5 1.8T QMS Spoiler/Garrett/Mintex/17" MM Spiders(in route!)

<i>Second, the factory downpipe provides some backpressure to help low end torque. This is evidenced by dyno runs after replacing it.</i>

I admit I'm no engineer, but I think this statement applies more to non-turbocharged cars such as the normally aspirated 2.8 V6. Too little back-pressure on a N.A. engine will hurt low-end torque. However, on a turbocharged car, the turbo itself adds backpressure. And this back-pressure remains even after you've installed a larger, less-restrictive downpipe. Everything I've read about turbo cars indicated that you want to dump as much exhaust as possible as quickly as possible.

Can you point me to these dyno runs you mention....I'd really like to see them. I'm not trying to say you're lying....it just goes against everything that I've heard in the past.

Thanks for any additional info you can provide.

<A HREF="Mailto:andy_hedin@hotmail.com">Andy Hedin</A>
'97 A4 1.8Tqms, Garrett 1.0 Bar, ABT Filter, APR/Borla Exhaust, Euro Headlights, more...

I should have said "evidenced by the dyno runs the race shop Stebro used" to develop their exhaust. Call Stebro and ask them for the full rundown, as I don't have the dyno sheets. If I did I would post them. They found that replacing the downpipe hurt low end torque and didn't have a benefit until the engine was at high rpm. They told me they didn't think this was worth the tradeoff of losing low end response and keeping the car streetable. Either that or they were not into designing a new downpipe as getting the fit right is tough, and the installation pain may not be worth the gains. Audi designed all these parts to work together. If you replace the exhaust, it probably is no longer a good match for the K03. If you replace the K03 with an 04 or 24 and also replace the downpipe with a bigger one, you probably keep things in better balance and the parts work better together (this is the route TAP takes you with their upgrades). I suppose you also need an ExtrudeHoned exhaust as well...

When I had the Stebro installed, the low end was very strong, and the car revved quicker. I have ridden in (but not driven) a 1.8T Passat with a full cat back (it also had a different chip than my car) and my perception was the low end was a little less, high end better, but there are too many variables here for any real comparison.

It is confusing. Several vendors lie about their exhaust being catback. As far as backpressure goes. I have only heard of one extreme case where a turbo needed more back pressure than was already inherent in the design (look at any picture of the kkk03/04 and see how small the outlet is and tell me you want/can get more back pressure than that!).

Our turbo is quite small. The case I am talking about had a separate wastegate and an open pipe exhaust, and yes, they did lose some bottom end.

The issue of it being a huge pain to replace the down pipe is true, and the performance gained is slight (with stock cat). BUT, that does not mean that you will lose torque if you put one on.

How about we refer to the two types as:

1) "cat-back" -- refers to the exhaust systems which bolt directly to the catalytic converter via a flange. Two that I am aware of are the Borla and the Neuspeed.

2)"Slip-joint-back" -- refers to the exhaust systems which connect to the stock downpipe via a slip-joint connection (exhaust pipe slides over the factory downpipe). Two examples are the Brullen and the Scorpion exhausts.

Andy Hedin
'97 A4 1.8Tqms, Garrett, ABT, A!, Borla, blah, blah, blah