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
Chris King wrote:
> Yeah, it's a mouthful, aint it? I printed the pdfs out over lunch and looked
>through them - the good news for you Bob is that there is a lot of info on the
>23D4 dizzys.
>
> Bad news for me is that there isn't much on the 45DE4's. But, I have the UK
>spec advance data in Bentley. *Theoretically*, if one knew how much the
>weights actually weighed, and their distance from the center of rotation, and
>given the advance data, one could back-calculate the spring force, and thus
>size the springs. (The vacuum advance thing is a whole other ballgame!)
>
> Evening reading (and re-reading) for sure!
>
> -=Chris
>
> Chris King - cbking@alum.rpi.edu
> http://members.home.net/kvcbk/
>
>
> ---------- Original Message ----------------------------------
> From: "Mueller, Robert CDR" <RMueller@grumobile.uscg.mil>
> Reply-To: "Mueller, Robert CDR" <RMueller@grumobile.uscg.mil>
> Date: Wed, 6 Feb 2002 13:28:14 -0600
>
> >That website is something else! It's going to take some time to digest all
> >of that.
>
> >Coastie Bob
> >'74 Midget
> >'90 944S2 Cab
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