7747 spark control questions.

[Bruce Plecan]

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.
>
>
>
>
>
>
> >
> > Are you saying you've had more cross tracking problems with the small
> caps?.
> > My experience has been the opposite..
> > I've also, never had a small cap rotor burn thru and dozens of the large
> > ones have done that.
> > Bruce
> >
> >
> >
> >
> > ----- Original Message -----
> > From: "Walter Sherwin" <wsherwin at home.com>
> > To: <gmecm at diy-efi.org>
> > Sent: Wednesday, October 18, 2000 9:19 PM
> > Subject: Re: 7747 spark control questions.
> >
> >
> > > I second that motion Bob, especially when using the 90mm "small cap"
> > > external HEI distributors so common in SBC and BBC ECM/PCM
applications,
> > and
> > > especially when using the stock cap/rotor setup.  Cross
tracking/jumping
> > is
> > > a real issue with these, especially with a better than stock ignition
> > setup
> > > and/or high cylinder loads.
> > >
> > > Walt.
> > >
> > >
> > > >
> > > > Shannen, if you don't mind, I would like to add one more item to
> > consider
> > > > when choosing the base (inital) timing. A v8 distributer is only
good
> > for
> > > > about 42 degrees of advance. This is a physical limitation.
> > > >
> > > > By setting more base timing, more total crankshaft timing can be
had.
> > This
> > > can
> > > > be good for things like aluminum heads and hi-way spark. You have to
> > > > balance this added inital timing against hot cranking stubbornness.
> > > >
> > > > BobR.
> > > >
> > > >
> > >
> > >
> >
>
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> >
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