Re: rotor for 20v turbo engine

[Sargent Schutt <sargent@novagate.com>]

I believe Lehmann is correct. Everything on my car appears to be correct, but
for some time now, I've had a problem with occasional 'misfiring/crossfiring'.
I've not felt anything like this before. It only happens on boost, and from
mid to high rpm's. THe odd thing is, it's more violent than say, a cylinder
missing. It is a real bad kind of feeling, and to say that one cylinder may be
firing in the wrong order, well, my symptom is what I imagine this would feel
like. 

I did not compare rotors when I changed mine, as I had to totally destroy the
old one to get it off, but I am very anxious to get the right one on there. I
may have other minor problems, but the most serious syptom is this occasional
misfire/borderline violent stumble. I would imagine this would also alarm the
ECU, and cause at least temporarily retarded timing, resulting in 'slower
response' some have made mention of in my '91 200q stumbling' inquiry. 

The rotor may not be the only problem, but I know of no other reason the car
should occasionally stumble like it does, in such a violent manner. (2.2 bar
TAP, K&N, Stebro)

Sarge

Brandon Hull wrote:

> Fact 1:
> 
> The proposition that the wrong sized rotor can cause cross-firing, leading
> to catastrophic engine damage comes from one of the highest authorities in
> Audi-dom:  Lehmann.  They replaced a blown engine which had been modified
> with their components, citing cross-firing as the likely culprit.  They gave
> the owner explicit instructions to use a particular rotor, and not
> experiment with aftermarket ignition wires in this very high HP engine.
> 
> Fact 2:
> 
> Audi/Bosch once spec'd a narrow rotor unique to the 20vt, which they still
> supply attached, when you buy a distributor, (Bosch) PN:  1 234 332 414 R1.
(snip)
> The "original" rotor, 414, is considerably narrower (by nearly half) than
> the 350.  It apparently has no other applications, hence it's
> discontinuance??
> 
> Fact 3:
> 
> Clearly, a too-wide rotor could cause cross-firing.  Just imagine a rotor
> head so exaggeratedly wide that it spanned two contact points simultaneously
> at the moment the ignition fired.
(snip)
> Brandon Hull
> '91 ersatz S2