More Distributor thoughts - long and nerdy

Wed Dec 10 07:38:08 EST 2003

Edited and commented
In a message dated 12/10/2003 1:19:12 AM Central Standard Time, 
cord4530 at writes:
Comments in the middle :o)

>>I'd agree...slop is a potentially huge problem. It's clear now that 
distributor geometry
>>*isn't* the main cause of failures.

Sure it is, by definition.  The geometry of a stock distributor/rotor design 
in size and splay with added high energy ignition means that the geometry is a 
problem when slop and high pressure are introduced.

>>To add to this, a high pressure air-fuel mixture seems to be extreemly hard 
for an arc to
>>cross. So, we have a corroded section of a tip facing a corroded terminal, 
connected to a
>>plug in a 'much less conductive than air' environment. While the clean 
leading edge of the
>>rotor has a (distant) view of a less corroded contact connected to a plug 
that's in nearly
>>astmopheric air. I could definitely see forward arcing happening. At least 

As my dad used to say, it only "needs" one failure to be catastrophic.  I'm 
with you on the high pressure thing is where "occasionally" could be 
catastrophic.  My own thinking is that the 4 valve motor introduction started this, but 
that non pressured 4 valve motors can tolerate slop and crossfire without 
failure.  I have no doubt it's still happening, just not manifesting.....

>>I also agree on this. I put a high power electronic setup in a normal Ford 
V8 cap. That >>was
>>a bad idea. Cross fire all over. But then, the spark would jump a full 
inch, and there was
>>less than an inch between could have been firing three 
plugs at once!

The documentation on conversion of HEI with stock distributors is pretty 
widely known in the ford and GM realms.  You can see the progression to the fix in 
just the applications to these motors over the years.  Why Bosch didn't go 
this route intrigues me.  No doubt audi/vw and bosch knew of the potential.  

>>I still can't figure out one thing. (Okay, there's MANY things I can't 
figure out) When
>>putting the new distributor in my engine, the window for correct placement 
was very >>small.
>>>I got no spark at all if I was + or - 2° off of the 'correct' location. 
Some of that is
>>>probably due to slop in my TB and chain. But it seems that if the slop in 
an engine got
>>>really bad, the ECU wouldn't get the signals from distributor and crank 
close enough to
>>>fire the coil at all.

Well, slop isn't *necessarily* a problem at starting rpm.  I've seen timing 
belts really loose that still start.  Usually you have rough running problems 
at idle (audi TSB Grp 28 Number 9303 applies to ALL distributor audis), but not 

> Summary:  Motronic turbo finally dictated a 30 year old distributor cap and
> rotor design obsolete.  Redesign the cap and rotor or go multicoil?  Thank
> goodness *something* good came of all this.

>>Yes, this is good. I think I'm sufficiently inspired to work on a 
coil-on-plug system for
>>the 20V engine.

My subliminal forces are working on you.:)  Then again, I chose the AAN for 
my urq transplant for my redneck views on distributors so shared.

>> Mihnea has convinced me that this may be a good idea. I'm already thinking
>>of some improvements for this next design. I won't have any time to work on 
this until
>>after this semester is over. And in reality, as a pet project it is likely 
to take me a
>>while. But at least it's a start. I should be able to do the design and 
prototyping (I have
>>a gearless distributor, and a 20V to try it on), but after some customer 
feedback and an
>>update, I really have no means of manufacturing this on any reasonable 

You get it done.  This list will figure out a way to get it produced.  If 
Javad can do EFI conversions, I doubt hardware should be a big problem. 

>>And since our campus got rid of Pro/E, I'll have to learn 
Solidworks....something I've been
>>meaning to do anyway :o) I'll keep the group posted.

Thanks for the discourse


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