I have been thinking about adding transistorized ignition to my TR4A. I had
thought about adding a transistor switching unit. I have a Pertronix right now,
but I am not at all sure it really adds any real benefits over a good condition
points system, other than not having points. But with a failure on the road
it,s a pain in the neck to reinstall the points parts. Plus the push-on magnet
ring does not fit well on my distributor. I was thinking about going back to
using points and add a transistor switching unit like the Boyer-Brandsen
Kit0069. That way if there were a failure, it would be real simple to go back
to points alone. With the transistor switching unit, the points will not arc
and the contacts will last essentially forever (maybe not the rubbing block,
though)
I have the Delco HEI sysem on my TR7 and I have done a bit of research on it.
It is a really nice system but requires a special low resistance (and lower
inductance) than the normal 3 ohm or 1.5 ohm coils. It limits current to 5.5
amps for the stock HEI unit and adjusts the dwell to JUST get to the current
limiting state before the ignition fires. This minimizes coil heating so it
won't burn out at these high currents.
I thought I might apply the HEI system to the points triggered TR4A
distributor. But if that is done, then dwell control is lost unless you use
some fancy electronics to convert points into a reluctor system. But then I saw
that the Lucas CEI ignition has the GM HEI module at its heart! What coil does
the CEI system use? I have not found reference to any special HEI-style coil
being used with the CEI.
Does the CEI system have a special HEI module that limits current to something
less than 5.5 amps? Or does it have a special HEI type coil? Or does it lose
the ability to adjust dwell and current and become a plain transistor unit like
the Boyer?
Here, I am going to get a little technical. I was thinking I could make my own
pseudo-HEI system by making a regular transistor switching unit, but then add a
current limiter. This would be a "12 volt" system, but would use a 6 volt (1.5
ohm) coil without a ballast resistor. The current limiter would replace the
ballast resistor. The current would be limited to that which the coil would get
at idle RPM with a ballast resistor.This allows the coil to saturate more
quickly (or at higher revs, just be closer to saturation) and therefore would
maintain spark energy to higher revs somewhat like what the HEI system does.
Also, this design would allow more current to get to the coil when battery
voltage is reduced during cranking, similar to the ballasted systems. From my
calculations, I think I should be able to have double the spark energy at
4000-5500 RPM.
And then there is Capacitive Discharge. I can see that CDI would be a good
design for very high RPM, like well over 5500. But I am skeptical that it adds
anything compared to a well maintained Kettering (points or transistor) system
at the RPMs we would have on the street with a maximum of 5500 RPM. I suspect
that the very brief spark(s) of the CDI system may not ignite the mixture as
well as a nice long 2-3 millisecond burn of an inductive system. The other
reason that I am skeptical is that auto manufacturers continue to use inductive
systems. They have gone to great lengths to do so, resorting to things like one
coil per plug, coil-on-plug, etc. If CDI were superior, it seems to me that it
would have been a LOT cheaper to use CDI than make these complicated inductive
systems.
I am looking for people's thoughts on these ignition systems.
-Tony
** triumphs@autox.team.net **
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