At 11:22 PM 11/10/97 +0000, Glenn Franco wrote:
>I recently stumbled onto an interesting distibutor set up for the TR6 in
>the green Roadster Factory TR6 parts manual on page 511. Listed under #1
>is a distributor kit that is a modified GM HEI distrubutor for the six
>cylinder engine. The obvious advantage of this conversion, although non
>stock, is its electronic, and the higher than normal spark plug voltages
Hi Glenn,
I have toyed with idea of making this type of conversion in my Spit/6. The
heart of the HEI system is the 'Ignitor module.' For purposes of this
discussion, the ignitor can be thought of as a solid-state replacement for
the points; although in later years the modules became much more
sophisticated. (in case you were interested, they are relatively simple
thick film circuits. The primary current is actually switched by two
transistors configured in what is known as a Darlington circuit) The early
'simple' GM modules can be easily identified since they have only four
electrical connections - the four pin modules. Two pins form the input
circuit, which is connected directly to a magnetic (Hall?) sensor. The
other two pins are connected to the coil primary circuit the same way a set
of points are wired. I don't remember how the dwell is regulated in the
four pin modules, but I suspect it simply a fixed number of crankshaft
degrees like a set of points.
If you wanted to modify your TR6 engine to use an HEI system, I would just
transplant the ignitor and the magnetic sensor; there is nothing special
about the distributor housing. Mount the sensor in your Lucas distributor
and the module somewhere convenient (it does need to be heat sinked). As
you state, it would be great to adapt the entire GM distributor from a
parts availibility standpoint, but the newer electronic distributors all
seem to be annoyingly large; they just don't fit well. Perhaps someone on
the list knows of a domestic unit lurking in a straight 6 that would fit
better (please tell me!). BTW, If you are thinking this sounds a lot like
the aftermarket ignition kits, you are right. I wouldn't be surprised if
you opened the aftermarket kits and found a four pin GM module, or a Ford
TFI, or a Hitachi module, or a Toyodenso module... In the late 70's and
early 80's they are all pretty much the same thing.
IMHO all these mods suffer from the same limitation, they rely on the
vacuum advance/retard and the mechanical advance system. The sophisticated
modification would be to use a simple digital controller and base the
ignition timing on measured engine RPM, manifold pressure, and coolant
temperature. Then you could use some of the new distributorless modules...
and an entire EFI system and ... and your modification can become so
complicated that it never actually gets done, like my plans to convert my
engine:-)
William Woodruff woodruff@fail.com
San Francisco, CA
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