Quote:
Originally Posted by KULTULZ
You've never seem a 3000 RPM LAUNCH on the street?
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I suppose, if people only drove at wide open full throttle you might have a point!
But again, there is no point to vacuum advance in drag racing in the first place, because there is basically only one engine operating condition and that's flat out wide open throttle. But we're not talking about that type of operation in ordinary passenger or street driven cars.
An engine designed to be driven on the street, puttering around town at part load throttle and varying speeds, RPM and steady cruise at highway speeds etc., requires an ignition distributor capable of controlling the ignition to meet very diverse operating conditions.
A simple centrifugal weight & spring mechanism alone could not achieve those requirements because the necessary timing advance "spread" or range for optimum fuel combustion characteristics was way too wide.
A typical OHV V8 from an engineering standpoint needs about 50° BTDC advance or more when cruising down the highway on flat ground in high gear. Drag racing engines simply don't "do" part throttle cruising, so it's irrelevant. If the distributor springs were light or flexible enough in a passenger car to allow for that much ignition advance at highway cruise, if the reluctor slots were long enough for that, then the engines would have been grenading left and right simply by driving normally around town. To get around this problem they ingeniously utilized engine manifold vacuum as an engine load-based signal to supplement centrifugal advance and met ignition advance requirements that way.
It is possible to use the engine itself as a kind of "distributor machine" for tuning purposes, but the only point I was making earlier was that the
specification listed in the shop manual, the nominal numbers themselves listed, are exactly half of what actually appear at the crankshaft. This was because of the assumption by Ford that a distributor was being set up and tested on a distributor machine, not by Joe in his garage with a timing light.