Exhaust questions (paging peter!)

[jdbubb at verizon.net (Dan Bubb)]

Timbo I know you're running MSnS-E although I don't know if you have a wideband O2 or not.
If you do have a WB-O2 you should be running closed loop to your AFR target table. In the area or 13.5 AFR at 100kpa increasing to 16 AFR around 50kpa. No richer than 13.5 AFR anywhere for a normally aspirated engine.
If you only have a NB-O2 you should tune the entire table to stochiometric then manually adjust VE table points up or down based on the proportion of the AFR you want to run to stochiometric.
I ran across a simple way to think about AFR recently.
At cruise you want to make sure you're burning all the fuel you inject for maximum mileage so you want excess oxygen.
At WOT you want to make sure you're using all the air the engine can breath so you run excess fuel. But there's no point in going excessively rich to the point of combustion inefficiency and actually loosing power. (unless you have a turbo and the excessive richness retards the likelihood of detonation!)

Getting back to the subject at hand, in my experience going from the stock VW dual downpipe to the TT dual downpipe gave a noticeable increase in power.

TT sells a high flow cat for their systems. Unless the ceramic core is bigger I can't imagine what's more high flow about it. All the TT cats have the same case size, and therefore core size, from 2" to 2.5" and the cores look the same, so I think mostly it's marketing hype. Just don't get something that has a smaller case size.
my .02
Dan

From: "Timbo" <timjmcconnell@xxxxxxxxx>
To: "Scirocco list" <Scirocco-l@xxxxxxxxxxxx>
Sent: Wednesday, August 01, 2007 12:30 PM
Subject: Exhaust questions (paging peter!)


> I'm pretty I need a new cat, because I've been running my car really
> rich for a while (better for engine, worse for the cat!).
> 
> The exhaust is going to be a 2" aluminized TT with a resonator, and a
> Dynomax. (Got it used, I would have bought a stainless, but hey - this
> was cheap!)
> 
> Should I get some sort of High-flow cat, or stock? What does the high
> flow cat come off of, or where can I get a new one. I need reliability
> and the ability to pass emissions first, but if there's no downside to
> going high-flow besides cost - I might as well do it.
> 
> And, is the TT dual downpipe worth it? I have a stock rabbit dual
> manifold, downpipe, and an almost new accordian flexy section. I even
> have both brackets!
> 
> --Timbo
> 
> --
> 
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