Mini Sprint history page, question about the distributor

[scooperman]

Interesting to read the Mini Sprint history http://www.minisprint.eu/page2.html however I am curious about the description of Neville Trickette's "twin point distributor that effectively ran at ½ speed to overcome point float at high RPM". I am having trouble visualizing how the rotor could be pointing at the correct spark plug location in a 1/2 speed distributor. Perhaps this is a typo? I have a twin point distributor but it doesn't run at half the speed of a normal distributor. It obviously does run at half the speed of the crankshaft, perhaps that is what the author meant?

[guru_1071]

two sets of points + two lobes = distributor which runs at 'half speed'

the gap between the points opening is, in effect, halved

the genius of neville

[scooperman]

You describe it as having two lobes. I assume you mean lobes spaced 180 degrees apart, therefore two sets of points positioned 90 degrees apart. To do this with one coil, the points are electrically in series, or are points which are closed by the cam lobes and are electrically in parallel. Nothing half-speed about this distibutor. It would operate but I fail to see that it could have any of the advantages of the traditional dual-point distributor. Normal dual-point distributors provide the means of adjusting the timing and dwell independently. One set of breaker points opens first, the other closes last, meaning one sees the opening voltage spike and the other see the closing voltage spike, so the points have half the arcing wear and therefore they last twice as long. The arrangement you describe still has the electrical/wear disadvantages of the single point distributor. It does have half the mechanical wear on the rubbing blocks, true, but dwell is still fixed by the lobe shape. I see the points wear issues as a concern for a street car, not a racing car, so I doubt if this was why Mr. Trickette chose this path. It would allow you to adjust the timing for cylinders 1 and 4 different from the timing of cylinders 2 and 3. I need to think about that, why that might have been useful.

My guess is this was an attempt to reduce points bounce after closing by reshaping the cam, before Lucas came out with the 54413568 points which were made for the Lotus Cortina and Cooper S. But I thought the asymmetric Lucas points cam was available long before this time, that would have solved a bounce problem.

[guru_1071]

My guess is this was an attempt to reduce points bounce after closing by reshaping the cam, before Lucas came out with the 54413568 points which were made for the Lotus Cortina and Cooper S. But I thought the asymmetric Lucas points cam was available long before this time, that would have solved a bounce problem.

this was the reason that neville made this conversion - it fixed the problems he had, so was obvilously a worthwhile modification

[Tim Harber]

All this is a bit technical for me , but I do have a question:

What do most folk use on FIA spec racers? I've got electronic fitted at present as Masters and others do allow it, but I'm not sure what I would want to fit as there seems to be so much rubbish about now

I did see this twin distribtor (Mallory I guess) on my trawl around cars when I was looking to build mine

[sandman]

I think many of us run Swift's racig condensor and 'S-points'... at least over here.

[scooperman]

The USA is pretty big, quite a few different race sanctioning bodies. Here in the southeast, HSR lets me run with the Electromotive crank-triggered ignition that was on the car (this car ran in SCCA from 1967 until 1980, then occasionally in the late 90s). In its early days it ran a mechanical tach-drive Lucas points distributor, looks just like a slightly taller Cooper S distributor. I believe this distributor was originally from some Triumph. In the 80s I modified my spare tach-drive distributor with an inductive pickup and the Hitachi matchbox coil driver box on the side of the distributor, and ran that for hotter spark at high rpm. For vintage, I bring the points distributor to the track in my spares box, it would only take a few minutes to change over to the distributor setup if I am asked to do so.

[mk1]

My original description is correct. The dizzy had 2 lobes 180° apart with two sets of points in it., The only thing it was doing was reducing the point bounce at high RPM.

Nice to know someone reads my stuff.