Quote:
Originally Posted by Lynn Eades
I think the timing jig is as much to set the dwell of the two sets of points as it is to time the dizzy, but as you say (once the dwell is sorted) then a timing light would be best. I have a timing jig but have not yet put it to use.
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Yes I believe you can read the dwell on the timing jig Lynn, but it's determined by the points gap, so if you set them to the recommended 14-16 thou the dwell will be correct. In practice however the dwell is not that critical, esp. with a modern coil. The old coils weren't nearly as efficient, and the idea of the twin point dizzy was to maximize dwell to improve coil performance. Basically it gives the coil a bit longer to charge up between sparks. Evidently coil technology had improved by '49 because the 8BA ran a single point dizzy, which by definition provides much shorter dwell.
Something else they did on the 8BA dizzy was get rid of the centrifugal advance system and replace it with a vacuum advance system, and quite an ingenious one at that. Gone are the flyweights used in the old dizzy, to be replaced by a vacuum diaphragm which runs off not one but two vacuum lines. One supplies manifold vacuum which advances the timing when the manifold pressure drops as the revs increase, while a separate line supplies venturi vacuum for load compensation. The two work together to provide a smooth graduated timing advance which is highly responsive to throttle changes throughout the full rpm range. As opposed to the old flyweights, which appear to be fully advanced at only 1500 rpm or thereabouts, as seen under the timing light, and the ON/OFF vacuum piston brake which only kicks in under load, and only retards the timing by about 5 degrees. It's far from ideal, and while it may only cost a few horsepower under full load, it would certainly cost in fuel efficiency at less than full load. There may well be a couple of mpg to be gained simply through improved spark timing, which is where your mapping idea becomes rather interesting Lynn. Or you could go the whole hog as you say and stick some injector plugs in, or even just a single point system in the throttle body, either of which would be quite easy and wouldn't detract drastically from original appearance. Who knows, we could be getting 15 mpg on the highway! When you consider the phenomenal improvement in fuel efficiency achieved in cars over the past 50 years, it's not entirely inconceivable.