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Re: [T3] Alfa Romeo's distributor

On 23 Jan 2004 at 21:37, Hal Sullivan wrote:

> At 10:07 PM 1/23/2004 -0600, Jim Adney wrote:
> >On 23 Jan 2004 at 19:36, Hal Sullivan wrote:
> > > For whatever it's worth, though, the Vanagon setup in my T1 hasn't had any
> > > problems in three years, and it's 100% used junkyard parts.
> >Hey, junkyard OE parts are still OE parts. They may be used, but they're the
> >best deal in town!  ;-)
> >I use used parts at every reasonable opportunity.
> I'm not knocking junkyard OE parts; I'm the same way! 

And I was agreeing with you, too. Just reinforcing your message. ;-)

> I don't know offhand what the coil puts out, but I'm pretty sure it
> doesn't have the resistance of the points-type.  Some Volvo owners
> (same Bosch ignition system) have been using 45kV coils with good
> results .. I wonder if that'd let me to widen the plug gap some more;
> I've been using .035 with no problems. 

While the coil determines the MAX voltage that might be available in the worst 
case, it's the SP gap that really determines the voltage actually reached. When 
the ignition system triggers (regardless of type) the voltage across the whole 
system rises until the voltage across the gap is sufficient to break it down. 
Until there is breakdown there is no spark.

Once breakdown occurs, the voltage drops dramatically, so that the spark is 
actually a much lower voltage thing, probably less than 1000 volts.

The only problem with wider gaps is that they require higher voltage to break 
down, so now all the other parts of the system have to go to higher voltages 
without breaking down. After all, the spark is just looking for the easiest way 
to ground and doesn't particularly care if that's across the SP gap or not.

I tried larger gaps (.040") with my CDI when my first squareback was new and 
found that it was fine most of the time, but in damp weather it was so bad that 
sometimes I couldn't even get the engine started. 

I finally got it started one night, and then looked at the engine. I could see 
flashes all along all 4 plug wires as they were just breaking down the air 
around them from the capacitive coupling thru the insulation. I reduced the gap 
and never had that problem again.

Your .035" might be fine, but you want to be careful that you don't get 
yourself in a position where you're stuck some cold damp night.

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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