Very good discussion about timing curves and dizzys (It made me dizzy to
read it) But unless
I missed something, you didn't explain the heating issue.
Your turn is over - NEXT!!
Thanks for participating
Larry
At this exact moment in time 7/25/00 15:01, PAsgeirsson@compuserve.com
made the profound statement:
>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@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@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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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.
|