Re: Re:reducing lag via exhaust efficiency

[Henry Harper <hah@srv.net>]

> 2*2.5" gives app. 38% larger area than 1*3"
> Kenn
> - -----Original Message-----
> From: Linus Toy <linust@mindspring.com>
> To: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
> Date: 25. marts 1998 22:27
> Subject: Re:reducing lag via exhaust efficiency
>
>
> >From: MHLIGGINS <MHLIGGINS@aol.com>
> >
> >> <<How much concern should I have for 3.0 bar boost levels on my
> >>173k mile motor?>>
> >>
> >>If you intend to have that much additional air into and out of the
> >>combustion chambers, you should seriously consider the 3"
> >>exhaust system.
> >
> >Don't forget that Sarge has a '91 200q - 20v.  this car has a dual exhaust
> >system from just after the turbo to the tail pipes (even inside the muffler
> >boxes, there are still two distinct pipes).  2x 2.5" pipes vs 1x 3"
> >pipe--the dual pipes may have an advantage.
> >--LDT
> >----------------------------------------------------------------------
> >* linus toy                       email:  linust@mindspring.com      *
> >* mercer island, wa                                                  *
> >----------------------------------------------------------------------
>

I had to get out the tape measure on this one. To clarify: '91 200q 3B stock 
exhaust system consists of
* icky stock exhaust manifold, we all know about it, not talking about that now
* k24 outlet is 2.5", joined by wastegate plumbing after oxygen sensor and 
several inches
* wastegate outlet is 1.75", the single downtube remains 2.5" after wastegate 
comes in
* 2.5" downpipe goes down about a foot then splits into two 2" pipes to go to 
the flat-cats, one on either side of the front differential
* two 2" pipes come back together out of the cats, travel together through the 
mufflers and end up under rear bumper (still 2")

So the downpipe is single, might benefit from an increase 2.5" -> 3" - then it 
has to split to go to the stock cats (or not...?). Who wants to start making 3" 
3B downpipes? I want one to go with my future fancy EM. How big is an MC-1/-2 
downpipe?

The downpipe is the most important thing to make bigger (yeah, after EM and 
turbo) because as gases travel down the exhaust system they cool and contract 
anyway, making 4" tips after 1.75" downpipes pretty silly. But we knew that 
before.

Wielding my keen geometric knowledge: a 3" DP at 7.07 in^2 will have a little 
more area than the two 2" pipes at 6.28 in^2. Not much of a problem given a bit 
of cooling. However the existing 2.5" DP only has an area of 4.91 in^2, pretty 
wimpy. It's starving the rest of the exhaust for flow, in fact. A 3" DP would 
be 44% bigger, and probably would fit pretty well, eh Graydon?

just a math fool,
Henry Harper
http://www.srv.net/~hah
1991 200 quattro, 86k, summer tires are back! yay!
1988 GTI 16v, 174k, summer tires are back, and no more 100 pounds of salt in 
back! even more yay! new stereo should be here today too...