7747 spark control questions.

[Shannen Durphey]

Waay back in 93 or 94, I was in a GM class where discussion turned to
the "new" optispark's failure rate.  Moisture and air in the dizzy
were being turned to nitric acid, and eating up the cap.  So we were
told.  The first thing I did when I got home was to remove my small
cap HEI and add a PDV system, positive distribtor ventilation. : )  I
used an old vacuum break from a Q-jet carb which had a small orifice
in it. I cut the off the vacuum line nipple, drilled a small hole in
the base of the dizzy, press fit the nipple into the hole, and
connected it to ported vacuum.  It's inexpensive, and so far it seems
like I'm safe from the "white cruddies".

Shannen

Bruce Plecan wrote:
> 
> Geesh, I must just be lucky then.  I'd heard of a couple bullentins, but
> nothing approaching what you've relayed here,  THANKS.
> I'd found two Dissys that were replaced under some program, and have used
> them, without a problem.
> Maybe, I just set things up a little on the rich side, and keep the firing
> voltage demands down enough that it isn't a problem???.
> 
> Just to expand on a theme here,
> Are you running slightly lower operating temps.?.
> I've been playing with some aftermarket GN stuff and they are generally
> tuned for a 160 operating temp, and I'm using a 190, and just moving the AFR
> a tad makes for a realllyyyyyy nice set up.
> I'm getting more convinced then ever that 190s are the only way to go.
> I know that flies in the face of what's commonly repeated as way to go
> faster, but it's just what works for me.
> Bruce
> 
> > Never really played with the large cap's  that much, so have no way to
> draw
> > a comparison between the two.  However, have had more problems than I care
> > to remember with the small caps, especially in the presence of boost and
> > better ignitions.
> >
> > At the best of times, the physical terminal spacing within the 90 mm cap
> is
> > way too close for comfort, greatly increasing the risk of inadvertent
> spark
> > jump to the next nearest terminal if you don't pay attention to the
> ultimate
> > spark limits in both directions.  The junk stock small caps were famous
> for
> > growing white whiskers of corrosion by-products off the ends of the
> > terminals, and also tracking carbon inside the cap shell, which would
> simply
> > make a bad situation even worse. Heck, throw in all the other afore
> > mentioned problems with the reluctor/shaft assembly & REF signal
> integrity,
> > and you have all the makings of a pretty unreliable unit IMO.
> >
> > You guys near the dealerships/shops will remember a whole whack of 6.0/7.0
> > litre medium duties with dead pistons, all thanks to these same
> distributor
> > root cause problems?  If you were to compile all of the associated small
> cap
> > Service Bulletins and TAC TIPS and part change-up references, you'd have
> > yourself a small novel for your book shelf.  Too bad GM muffed the single
> > most important bit of EFI hardware for so many years.
> >
> > Now in GM's defense......they finally got their "stuff" together by about
> > 94/95, just in time to stop using that distributor in the vast majority of
> > applications:).  The latest V8 service distributor assemblies that I have
> > bought (1103952) seem to be pretty good, although I still sometimes add a
> > good cap and rotor an extra bit of peace of mind.
> >
> > Walt.
> >
> >
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