Hi All,
Not wnting to get in a real pissing match here, but I would like to drop in
a few items.
The majority of the performance Spridgets are running 1275's. The dizzys on
these engines that were sold in the states had less centrifugal advance
than did the 1098 dizzy or the 948 dizzy. This was done to be able to
reduce the emissions on the 1275. Most of these dizzys had a vacuum
advance unit on them, the exception was the 23D4 which didn't have one.
Now the centrifugal advance unit varied from 12 to 16 degrees and also
varied by what RPM they kicked in and advanced. The vacuum advance units
that were supplied or were initially available varied from as low as 4 to a
high of 8 degrees advance. I think the only one still available in the
parts store is a 4 degree one.
With a generally recognized maximum advance on the timing to prevent
destruction of the engine being about 30 degrees, it's pretty easy to
figure out where you should have an initial dynamic timing set.
An example would be something like this.
Total vacuum advance= 6
Maximum centrifugal adv= 16
Dynamic timing set 8 BTDC
________
Total advance degrees 30
This would likely keep you out of trouble for early destruction of your
engine. The reality of this example is it is based on a 948 dizzy. If you
had a 1275 dizzy it would be more like this.
Total v adv 2
Max cent adv 12
Dynamic timing set 8 BTDC
________
Total advance degrees 22
This would hardly get you into a decent performance bracket so advancing
the dynamic timing another 8 degrees would still keep you in the total
degree range of 30. However, it would alter the performance
characteristics of the engine, flatter at lower RPM or vice versa, or
flatter at higher RPM or vice versa, depending on your carburation, cam
design and CR.
Remember that you might not ever get to the advance feature of the vacuum
unit if you are driving with your foot stuck to the floorboards and the
vacuum will never be high enough to advance the timing.
Putting a dizzy on a dizzy machine and getting the right response curve
built into it is usually money well spent. Another cheaper option is to
use an earlier dizzy, one from a 948 or 1098 to get greter advance over a
longer range of RPMs. Another way is to keep playing with your dynamic
spark setting and leave it where it works the best. If you have electronic
ignition, then you would never have to fuss with that again
The 23D4 dizzy usually calls for a dynamic spark setting of 22 BTDC. I
don't know the advance on this dizzy, but it is likely about 14 degrees.
With all the variables that we put into our engines in head improvement,
exhaust extraction or nor, carburation and ram pipes, compression ratio and
cam design, it's entirely possible that all the responses to this initial
thread are in the correct category, or close enough to be right. A huge
variable could possibly be whether or not Zappa is on the stereo or you
have a cat stuck in the undercarriage!
There may be a few minor technical errors here, but I think you can get the
picture fairly well with the above illustrations, and I also don't have a
spell checker on this e mail program, so don't send over the spell cops!
FWIW, Paul A
FROM: Bryan Vandiver, INTERNET:Bryan.Vandiver at Eng.Sun.COM
TO: Larry Macy, INTERNET:macy@bblmail.psycha.upenn.edu
spridgets, INTERNET:spridgets@autox.team.net
Larry Miller, INTERNET:millerls@ado13.com
DATE: 7/25/00 1:32 PM
Re: Re: Timing Vs Over Heating
FWIW - I just changed the timing om my 1275, from 8 degrees BTDC, to 16
degrees
BTDC, about a week ago. The car is now running hotter.
I also noticed that the more retarded the timing is, the power band shifts
to
higher RPM, and the more advanced it is, the power band moves to lower RPM,
and
becomes flatter. Any thoughts on this??
- Bryan
>Subject: Re: Timing Vs Over Heating
>To: "Larry Miller" <millerls@ado13.com>, "Spridgets@Autox. Team. Net
(E-mail)"
<spridgets@autox.team.net>
>Mime-Version: 1.0
>
>Well for what its worth, I always heard it was too retarded makes it run
>cool, something like not burning all the gas and leaving liquid fuel in
>the cylinder. (That is likely as far off the wall as it is off the top of
>my head)
>
>Too advanced makes it run hot, the engine is working too hard and
>compression is not finished before the spark front hits the A-F mix. the
>engie then has to compress the exploding gases.
>
>At least that is the way I answered it when I applied for the "Who Wants
>To Be a Millionaire" show.
>
>Larry
>
>At this exact moment in time 7/25/00 12:46, millerls@ado13.com made the
>profound statement:
>
>>>From: "Toby Atwater" <Toby@intri-plex.com>
>>> I always heard kind of the opposite. Spark too advanced (early) will of
>>> course ping. Spark too retarded (late) will result in a loss of power
and
>>> overheating. It kind of makes sense. There is the same amount of
gasoline
>>in
>>> the charge but less power is developed, the wasted energy goes into
heat
>>> instead of usable pushing power. That is how it was explained to me...
>>>
>>> Good luck
>>
>>Toby
>>I don't have an over heating problem I just wanted to hear some thoughts
on
>>timing Vs over heating.
>>
>>Thanks,
>>Larry
>
>
>Larry B. Macy, Ph.D.
>macy@bblmail.psycha.upenn.edu
>System Administrator/Manager
>Neuropsychiatry Section
>Department of Psychiatry
>University of Pennsylvania
>3400 Spruce St. - 1015 Gates
>Philadelphia, PA 19104
>
> Ask a question and you're a fool for three minutes; do not ask a
>question and you're a fool for the rest of your life.
>
>
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Date: Tue, 25 Jul 2000 10:17:45 -0700 (PDT)
From Bryan Vandiver <Bryan.Vandiver at Eng.Sun.COM>
Subject: Re: Timing Vs Over Heating
To: millerls@ado13.com, spridgets@autox.team.net,
macy@bblmail.psycha.upenn.edu
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