Quick Car, but too rich?

[Brett Dikeman]

At 2:19 PM -0500 11/28/04, David wrote:
>Man, this is one fast Audi, but it seems to be running a little rich 
>at idle... http://www.323gtr.com/media/oz_mpeg1_web.mpg
>

Anti-lag and and launch control, and I'd say it's well set up. 
Apologies for the atrocious explanation which follows, it's late.

They are rarely properly implemented- you need to run custom engine 
management to do it properly; no chip will do that.  You have to do 
funky injection and ignition tricks to make sure there's oxygen to go 
with the fuel; the mixture has to combust in the exhaust manifold, 
not coming out the tailpipe.  A higher idle is also necessary, as you 
need enough oxygen for the combustion.  2,000 rpms or so is I think 
normal; more than twice normal idle RPMs.

The launch control aspect allows the driver to keep the throttle wide 
open, and is activated typically by a clutch pedal sensor and/or 
shift gate sensors.  Clutch goes in, various tricks are used to keep 
tons of hot air going through the engine but not make any power, and 
soon as the clutch re-engages, timing and injection go back to normal 
and BAM you've got power.  The two do similar things and are often 
implemented together, but accomplish their goals in slightly 
different ways.  One is designed to allow the throttle to remain open 
but keep the engine from making power; the other is designed to 
explosively spin the turbo.

Most systems you'll see on street cars are complete posers, causing 
little pokey fireballs out the back when the hot, super-rich mixture 
finally hits oxygen and combusts.  I've seen cars (I will not mention 
any names) with engine management done by Dahlback that do precisely 
this.  One proud owner declared, "oh, that's the anti-lag".  Okay, 
sure...

   The true systems do what the car in the clip does- cause loud 
bangs, eject red hot pieces of carbon, etc.  It usually also causes 
extremely premature turbo and exhaust failure, both due to the 
stresses of the explosions in the manifold, and the extremely high 
temperatures that are much, much higher than they usually would be. 
The professionally built systems (ie those used by rally teams) often 
incorporate cool-down modes for when the car has finished a run/stage 
to sharply drop average EGT (ie shutting off cylinders aggressively 
to pump cool air through, setting mixture so EGT out of a firing 
cylinder is low, etc).  Most also have selectable aggressiveness, 
both for driver preference and race dB limits.

Brett
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