4-cyl HEI in GM Autos?

[Clare Snyder]

Clare Snyder wrote:
> 
> Garfield wrote:
> >
> > On Thu, 27 Nov 1997 10:16:33 -0500, Clare Snyder <clsnyde at ibm.net>
> > wrote:
> >
> > >Why would the advance be different? It is X number of degrees, period.
> > >The six cyl unit should work just fine. Even an eight should work. Check
> > >with NAPA, you will likely find the same module used on the 305 and the
> > >4.3 carbureted engines. Mabee even the same on 4.3 and 5 litre efi.
> > >Take your 6 and a timing light, and check the advance curve with the ecm
> > >disconnected. Does the advance slowly advance, or does it jump?
> >
> > Uh, I already said, I DID that. Once more with feeling: It jumps +8deg
> > when it starts the advance ramp at about 2Krpm, and then "ramps", not
> > jumps, up another +10deg as I open the throttle. Just fineNdandy what
> > I'd like.
> >
> > As to it working on a 4 just same as a six because "it's the same # of
> > degrees", think about it. The module doesn't know the rpm except by how
> > many pulses it's receiving. And it doesn't know "degrees" either, only
> > pulses and how far apart they are in absolute time. Doodle some on paper
> > to check yerself on this. A degree is a degree is a degree, but a pulse
> > isn't a pulse isn't a pulse, ifyaknowadamean.
> >
> > Garfield
> >
> > P.S. Easiest way to see the module CAN'T work the same on 4s, 6s, and
> > 8s, is to consider at what rpm the advance is gonna kick in at all. Eh?
> > If it's at 2Krpm on a 6, at what rpm will it be on a 4? You've got 2
> > less pulses coming to the module per rev, on a 4 vrs a 6. But the module
> > doesn't know this. It's just counting pulses per time period. So how's
> > it gonna know the rpm? if it doesn't know the #cyls? it's dealing with.
> > N'est ce pas?
> 
> I don't know about the GM HEI, but the B&S Magnetron functions on the
> rate of rise on the signal. The faster the engine turns over, the
> quicker the pickup signal rises. Because the pickup signal must reach a
> particular value before the ignition triggers, the faster the engine
> turns the sooner, in degrees, the ignition fires.
> At low RPM the ignitor does not fire untill the reluctor actually passes
> the core of the pickup coil. At high speeds the voltage reaches the
> firing point about 20 degrees before the reluctor passes the core of the
> pickup coil. This is how that ramp happens.
> At least that is how it was described to me by a B&S expert. The whole
> thing makes sense, as it can only work with magnetic pickups, not hall
> effects or point triggers, which are self controlled switches.
> Think about it, then try it and see if I am right.
> Just connect an old HEI dizzy to either a dist machine or a variable
> speed drill and crank it up with a timing light connected to one cyl,
> and a white mark on the chuck. Check the timing advance at several
> speeds, then knock a couple teeth off the reluctor wheel and try it
> again. Just don't knock off the tooth triggering the wire you have the
> timing light on. I think you will find the advance does not change much.
> Otherwise the module would require a time base, which it does NOT have.
> The module is totally passive - simply a level controlled switch, or
> amplifier with hysteresis, from what I have gathered.
> Now, as usual, I could be wrong, but now you know how to find out, and
> why it works if it works.
> --
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> 
> Remove the R from E-Mail Address to reply. Stop the spammers!!!
> It's hard to soar like an eagle when your stuck with a bunch of
> Turkeys
It's official!

The same module is used on 4,6,and 8 cyl vehicles. Echlin/Napa part#
TP25 fits the following, and mabee more:
92 spectrum 1.5L
86 Cavalier 2.0L
86-90 Caprice 4.3L
86-88 MonteCarlo 4.3L
1990 Caprice 5.7 pursuit
1989 Caprice 5.7
88-89 Camaro 5.7
87-88 MOST 5.0L

TP22 fits the following:
83 Cavalier 2.0L
90-92 Camaro 3.1L
88-89 Camaro 2.8L
 etc


I'm not going to say "I told you so", or rub your face in it or anything
:} Just go for it!!!!
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Remove the R from E-Mail Address to reply. Stop the spammers!!!
It's hard to soar like an eagle when your stuck with a bunch of 
Turkeys