FW: [s-cars] Stebro vs. Stromung exhaust

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CP:
Comments inserted.
In a message dated 5/28/2003 10:47:58 AM Central Daylight Time,
cpayne at bconnected.com writes:

>Scott,
>  In regards to your last comment: "Bottom Line:  Audi builds darn nice
turbo >exhausts from the factory.  You can go "bigger", but really tough to equate
that to >"better""

>  I think that the UrS4 had a decent heavy and very mellow exhaust that
flowed >pretty good via it's dual pipe nature.  However I think that if you look
at the B5 A4 >and B5 S4 and the performance gains you get with just an full
exhaust + chip you >would see that there is a lot of restriction in the OEM
systems.
>  Lets take a look at the numbers for the B5 S4:
>   - Stage I Chip 305 HP (Get on the throttle sounds like a sand blaster)
>    - Stage II Chip + Cat Back 320 HP
>    - Stage III Chip + Full Exhaust and DownPipes 340 HP

Er, the B5 has it's own problems with flow, 2 turbos tend to do that....  I'd
also venture that the cat is the biggest restriction to flow (audi norm) and
that appears confirmed by the above.  It's also my experience that after the
Cat, improving the downpipe can yeild good gains, that would also support the
above.  If not designed properly, it can also yeild no gains as well, only
losses from the wallet

  Lets take a look at the B5 A4 1.8T:
>    - Stage I Chip 187 HP (Sand blaster sound)
>    - Stage II Chip + Cat Back Exhaust 210 HP
>    - Stage III Don't have numbers that only include DP and Cat and not a
K04

Around 240 IMS.  I actually did this one in stages, lastly including the
k04.  The cat almost completely melted before stage III.  The difference here is
that audi puts the cat really close to the turbo, so heat is a problem.  No
question that the cat is THE restriction on the above, I pulled the downpipe from
the turbo still hot.  Molten red, in a full daylight shop.

> Finally the C4 UrS4/S5:
>   - Stage I+ 280 HP
  >  - Stage II Chip + Full Exhaust?! or RS2 Manifold?!
  >    - I would "guesstimate" it to be around 300 HP w/ the Full Exhaust
  >      - Has anyone done headers only w/ stock exhaust + chip?
>    - Stage III Chip + Full Exhaust + Headers HP Unknown Guess 320?
>   - Stage IV RS2 + Full Exhaust 350-380HP depending on tuning
  >  - Stage V RS2 + Full Exhaust + FMIC 400 HP
>   - Stage Hap/Mike The works... ALOT OF HP!!!



>In all 3 systems above the turbo has not changed and have only decreased the
>resistance of the stock OEM system..and going from Stage 1 to 3 software >
programming has changed.  In my past experiences/ownership of the B5 (S4 and >
A4) going from Stage 1 to 2 the software did not usually change (MTM and ABT)

The point is, RESTRICTIONS can be measured.  In the stock audi systems, the
first culprit is the cat/s, btmt.  The next restriction is usually the downpipe
(tough to measure, but yields gains higher than the mid muffler IME).  The
the next restriction is the mid muffler, then lastly the rear muffler.  Changing
any of the above in/out of order changes the "next" restriction....

>  Now "was" exhaust restriction on the C4 UrS4/S6 an issue? I don't have the
>numbers...and perhaps Mike P's test will put some light on the issue.  I
also don't >know what the MTM RS6 gains w/ the full exhaust...perhaps Fredrick
can expand >on this.
>  What I can tell you is that when I went from my stock system to the >
Stromung...I noticed quicker spool up by 300 RPM to full boost via boost gauge >
comparo.  I also noticed that she pulled harder at the higher RPM's....

Stromung system is good, no question.  But, you just bagged and tagged it as
better.  A cheap SOB could get just about all of it with a stock system and a
set of cats.  Then a Hapersize customer for instance (yea I get em too:),
could do a dual 2.5in exhaust with a 3.5 in downpipe, and really have the cats
meow.  btmadet


I really have no interest in giving away my farm CP, but I've been working
audi turbo quattro exhausts for over 10years, starting with a 3in turbo back
with single flowmaster in 1992 on a 5ktq.  That 20vt exhaust from the factory is
damn good, and with some proper tweeking of the dual cats and the mid muffler,
yield numbers that the Stromung might find challenging.  The simplest thing
to do is just pony up for the Stromung.  The hardest thing to do, is try to
"justify" it by performance.  IME/O, the key is just backpressure measures.  You
do them and address them properly, the dual exhaust audi delivered is most
adequate for the task at hand.  It doesn't look as cool, it's not as light, and
you can't polish the tips.  But I'm speaking ONLY of performance here.

Take a gander at page 133 of Corky Bell's book.  We might all be agast at the
idea that a single 2.25 pipe is good for ~300hp, Audis "restrictive" 2x2.25
pipes at 600hp?????  Maybe not, but I'm betting and measuring that the pipes
aren't the problems, in any of the audi turbo exhausts you mention

HTH

Scott Justusson
QSHIPQ Performance Tuning