7747 spark control questions.

[Walter Sherwin]

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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