7747 spark control questions.

[Len Sabatine]

     For  General Principals , '95 and later LT1s have forced ventilation , 
Opti
     has Vac bung in Housing as well as the Cap . This system appears to
     work slick to keep moisture intrusion and resultant "Cruddies " in check.
     Len
>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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