Paul -
An interesting thread, eh? I seem to remember cautions about the
possibility of "over-advancing" with a worn 25D under continuous full
throttle operation (the long straight at Buttonwillow?). Have you ever
seen this actually occur?
regards,
Clay L.
'67 Sprite
At 03:54 PM 2/6/2002 -0800, Paul A. Asgeirsson wrote:
>Hi Chris,
>
>Out of lurk/observation mode! I have one of these dizzy machines,
>vacuum pump and all. Cool device.
>
>I think that there is no calculation based on the actual physical
>weight of the weights on the dizzy, but rather how much is the actual
>curve on the nested weight and center piece and the effect of the
>springs that allows it to advance. It isn't the weight that matters
>but what the weight was machined to advance the maximum and when it
>occurs is the function of the RPM and the strength of the springs.
>That maximum amount is usually stamped on the weights in the dizzy.
>
>That said, you will still need to know at what RPM you want the
>advance curve to start at and at what progression through the RPM
>range and what you wnt it to end up at. If that is known, then the
>dizzy dizzy machine can help you. It won't do the advance
>calculations for you, just the verification of what it delivers.
>
>About the vacuum advance, this is essentially useful only at high
>vaccum of the engine, which usually is of no consequence on a
>performance engine. That's the reason there is no vaccum advance on
>the 23D. On a street engine the vacuum advance might be as high as 6
>degrees which is on top of the sum of static and advance timing and
>will occur only when the engine has vacuum of usually more than 14
>inches. To get that you are cruising with very light throttle at
>light load. When you give the engine more throttle, the vacuum drops
>and so does the vacuum advance (no vacuum, no vacuum advance
>function,) so you will avoid pinging or detonation when it's pulling
>hard. Running the engine with very light load and extreme advance
>timing usually isn't a problem, but when you put a load on it, the
>timing needs to drop back some to preserve the engine.
>
>I took an Allen tune up course on this machine more years ago than
>should be admitted! Suffice to say it was pre Bug Eye!!
>
>Paul A
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