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drag race engine ignition systems

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drag race engine ignition systems

Postby Dragsinger » Fri Oct 16, 2009 6:44 pm

Lately several post on message boards have talked about ignition systems designs with a problem of "retard" as RPM increases, thus, hurting performance.

So, Let's talk about proven drag race engine ignition systems. Specifically, carburetor, high compression combinations running at least 7800 -8200 RPM's

What has proven, long term to be effective, no tricks, no latest deal, just stable, reliable service.

In addition, lets talk about distributor vs crank trigger usage.

I will enjoy hearing about your on track, real world experience.
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Postby bill jones » Fri Oct 16, 2009 7:32 pm

-here's part of an answer I posted on the MSD ignition forums some time back.

"magnetic triggers exhibit a tendency to retard the timing as the rpm changes such as: the common practice of setting timing at some low rpm liker 3000, then racing at 5500 to 8500 rpm and never checking the timing at race rpm.

-most people I encounter never check timing at those high rpm but that is the only rpm where timing really counts.

-magnetic triggers need to checked and compensated for the magnetic hysteresis retard issue.


-here's another of my replies on MSD

"Of all magnetic triggered ignitions I've seen---that have a locked rotor----the timing will retard a degree or so per thousand rpm because of what is called "magnetic hysteresis".

-Hysteresis is lack of the magnetic trigger ability to keep up with the rpm so the magnetic trigger signal lags behind slightly as rpm increases.
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-I think the windings inside the ignition coil have a lot to do with this lag---and different types of magnetic triggers also have a large effect.

-Using the same box & coil but triggering them with 5 different magnetic triggers such as a Chrysler, a Ford/MSD, an HEI, a Bosch metal shutter wheel or a magnetic crank trigger all change the amount of retard.

-Typically I see and have to deal with about 8 degrees of retard when the rotor is locked depending on the total rpm range.
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-So it depends on what rpm you "test" the timing at---like if you checked the timing at 3000rpm and again at 7000 rpm you might see something like 6 degrees of retard---where if you if you tested at 1000rpm vs 7000 you might see 8 to 10 degrees of retard.
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-What you are dealing with is very common and I think the only way to make the timing stay exactly where you want it thruout the entire rpm range would be to use a timing computer of some sort."


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-all of those threads on MSD can be found searching Google with the following: magnetic hysteresis bill jones site:msdignition.com
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Postby bill jones » Fri Oct 16, 2009 7:59 pm

-99 percent of every ignition I've dealt with has been distributors like GM HEI's, Fords DuraSpark, and MSD distributors with the Ford style magnetic triggers-----and about 90 percent have been oval track----and the ignition boxes were typically the MSD6's or 6AL's.

-I have had ignition testing machines since the early 1970's where I can test and modify complete ignition systems and crank triggers etc to about 10,000rpm.
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-One issue I have seriously dealt with when running distributors that contain the ignition trigger is rotational slop between the distributor gear and the cam gear---which is quite frequently around 3 degrees of uncontrollable timing scatter.

-This can be helped with oversize pitch distributor gears and attention to the exact height orientation of the distributor gear in relation to the cam center line.
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-But---to fix ALL of the slop the only way I found to fix it requires offsetting the distributor shaft by installing a purposely offset lower bushing----to move the distributor gear several thousands closer to the cam.
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-Having not dealt with more than maybe a dozen crank trigger systems I know the original magnetic trigger systems that MSD used---that had metal reluctor tabs----have been obsoleted in favor of the flying magnet system----and there was timing retardation when using the original system.

-I really do NOT know how much if any the flying magnet system retards--and I have yet to test any of the MSD digital boxes----I've heard they do not retard
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-any ignition system that uses a distributor for the plug wires--where the timing trigger is remote from the distributor such as a crank trigger and/or any type of electronic ignition timing controller---the distributor always needs to be checked & rotated to get the rotor indexed to coincide with the timing event when the engine is running.
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Postby bigjoe1 » Fri Oct 16, 2009 10:38 pm

This is one of the BEST REASONS I have ever seen to run your engine on an engine dyno. When I am test on the dyno, I set the timing at some basic setting, then , I move it to where the engine makes to most power. I dont even bother to see where it is at untill I am all done testing, then I verify where it is at with the timing light..I usually set the timing at some easy to use RPM ( like 5000 )It does not matter where it might move to at 7500 ( retard or not ) because I set it where it makes the best power

JOE SHERMAN RACING ENGINES
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Postby BrazilianZ28Camaro » Sat Oct 17, 2009 1:56 am

And how about the optical triggers like Mallory's Unilite systems?

They retard the timing with rpm?
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Postby Tuner » Sat Oct 17, 2009 2:35 am

The phenomenon you guys are experiencing is the “slew rate” of the circuits in all the electronics involved, the ignition amplifier, the rise time of the coil, the rise time of the voltage in the plug wire and at the spark gap, and last, but not least, the slew rate of the timing light. All electrical devices have a fixed time it takes for them to perform their function. Every part of a circuit has a time constant, in electronics jargon called ‘slew rate’.

http://en.wikipedia.org/wiki/Slew_rate

Every electronic circuit has a fixed amount of time it requires to change state from off to on or from one voltage to another. In the case of ignition amplifiers, magnetic triggered or otherwise, the devices have a fixed time from the trigger pulse to the change of state of the output. It is common to see a ‘rise time’ specification for ignition systems and particularly coils. The difference in rise time between CD and induction systems is often mentioned.

A device that has a lot of transistors in it, like the detector or pre-amp in an ignition system or the micro-chip calculator in an adjustable timing light, can be pretty slow because it has a slew rate for each transistor and the delays are additive. For the device to function each transistor in turn must switch from off to on.

The bulb in the timing light has a fixed time it takes for it to achieve incandescence from its off state. Xenon and neon are the gases in flash tubes. Xenon is most common in modern timing lights and more desirable for two reasons, its brighter white light and faster rise time than Neon, which has an orange light.

The bottom line of all this, and the reason you see the retard in your timing (all else in good shape, no mechanical gremlins like the cam walking) is at high RPM the crankshaft moves more degrees closer to TDC in the same amount of time.

To illustrate (these numbers are not actual, but for example only), if the ignition and timing light use 1 millisecond every firing, and that is one degree at 1000 RPM, it will be 6 degrees at 6000 rpm. The crank will travel 6 times as far in the same amount of time because it is going 6 times faster.

To see the timing be 36 degrees at 1000 RPM the actual trigger event (points open, VR triggers, Hall effect switches, whatever) will have to be 37 degrees. At 6000 RPM the trigger is still 37 degrees but the crank moves 6 more degrees in the same time it took to move one degree at 1000 RPM, so the light shows 30 degrees.

For some perspective do the math: 6000RPM / 60 = 100 revolutions per second X 360 degrees = 36,000 degrees per second. Each degree is 1/36,000th of a second or .00002778 sec. 8000RPM is 48,000 degrees per second.

All systems that don’t calculate the timing from the previous cylinder’s firing event exhibit this retarding phenomenon to some degree (pun intended) and unless someone figures out a way to repeal laws of physics as old as the universe, that’s just the way it is.

Not all ignition amplifiers have the same slew rate. Some are much slower than others. Some are as slow as two degrees (or more) per 1000 RPM. The Ford Dura-Spark and Mopar ‘orange’ boxes are particularly slow. The actual “Chrome NASCAR Box” Mopar sold in the late 70’s is not in the slow category, but your chances of ever seeing one are nil to zip. Genuine GM HEI modules are about the same as MSD and other CD boxes, with about 1° or slightly less retard per 1000 RPM. Aftermarket HEI modules can be as slow as 2° (or more) per 1000 and some of them seem to be voltage sensitive, lower voltage makes them slower. Aftermarket modules of the same brand, part number and appearance can have different behavior. So far, actual GM modules I have handled have been the same (in slew rate) since they were introduced in 1974.

Ironically, because a points system has only one switch - the points, a properly functioning points system will have less retard than electronic systems. 35+ years ago, when a good points system was replaced with electronic it was common to lose performance because of the retard, in spite of more spark energy.

An ‘ah-ha’ moment came in connecting the dots between the advice of Smokey Yunick, Bill Jenkins and FoMoCo, all of whom advised timing curves for specific engines which advanced the timing a degree or two (or more, in some cases) all through the engine’s power range and sometimes beyond the operational ceiling of the valve train. This was proven to work well with points and with a little tweak of softer springs or a different cam shape, was adapted to negate the slew retard of the amplifiers and provide a fixed total or advancing timing as desired. The mechanical advance can be set to advance the same amount as the electronics are retarding.

It is unfortunate you guys who never raced 8000+ RPM engines with points missed the experience. I used several hundred sets of D112P Delco points in the two decades between the early 60’s and the early 80’s. Big Joe knows what I mean, I’ll wager.
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Postby aussie mouse » Sat Oct 17, 2009 7:33 am

bigjoe1 wrote:This is one of the BEST REASONS I have ever seen to run your engine on an engine dyno. When I am test on the dyno, I set the timing at some basic setting, then , I move it to where the engine makes to most power. I dont even bother to see where it is at untill I am all done testing, then I verify where it is at with the timing light..I usually set the timing at some easy to use RPM ( like 5000 )It does not matter where it might move to at 7500 ( retard or not ) because I set it where it makes the best power

JOE SHERMAN RACING ENGINES


Joe has it in a nutshell, when the engine makes best power, is where tiiming in Drag Race engine should be.
Crank triggers are the best, they provide the most stable timing.
All magentic pick up ignitions suffer retartd at high rpm , so long as you know what makes best power, that is all that matters, if your light says 36 deg at idle with locked timing system, who care if it has only say 32 or 34 at 8500 rpm, if it makes best power like this, then so be it.

Most aftermarket type igntions , however do have compensation built in to counter the effects of the high rpm retard that occurs, and this is where you can come unstuck, different igntion systems will compensate differently, also different igntions with different spark dwell may require slightly differnt igntion timing. :D
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Postby Tuner » Sat Oct 17, 2009 10:41 am

The trigger, magnetic, photo cell, or otherwise, is not the reason the timing retards.

The ignition amplifier and timing light electronics cause the observed retard.

As Big Joe and aussie mouse are saying, the point is moot when the timing is set by engine performance.
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Postby Dragsinger » Sat Oct 17, 2009 1:13 pm

Mr Tuner,

I really appreciate your lessons. The electronics review was good, through the years we are exposed to these lessons, but with time the lessons become dim.

Thanks for the refresher.
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Postby ZIGGY » Sat Oct 17, 2009 1:19 pm

X2 to singer's comments. Thanks Tuner. Good reading.
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Postby fastvette » Sat Oct 17, 2009 1:54 pm

Ok so I build an engine, dyno it and set timing to make the best power, with MY timining light and MY ignition box. Customer puts it in the car and use a different ignition box and his timing light. Now what do we have? Close? Way off?

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Postby bigjoe1 » Sat Oct 17, 2009 2:22 pm

I am having this PROBLEM right now with my own sons race car. His MSD box moves the timing quite a bit, and nobody seems to know why..We have just been resetting it back to the number we saw on the dyno, but I am not sure it is correct

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Postby Dragsinger » Sat Oct 17, 2009 4:38 pm

Then answer me this, which MSD box has proven to be the most stable and reliable? The older analog 6AL or 7AL or the newer #6 or #7 boxes with a processor?

At this point, I have 35 years of satisfactory usage from the analog boxes. Do I need to joint the digital ranks or hang onto the old?
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Postby bigjoe1 » Sat Oct 17, 2009 4:56 pm

That is my problem.. I have a Digital 7 on the dyno, and the kid has an old 7_AL in the race car. Theyboth seem to run very well, but we just have to reset the timing from one to the other. There is a real big differance in where the timing is set just changing the two boxes ( about 12 to 14 degrees)


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Postby fastvette » Sat Oct 17, 2009 5:15 pm

I have it the other way, 7AL on the dyno and digital 7 in the car and see at least 10 degrees differance in timing. That don't bother me much, but what about at peak power? What is the timing doing? Do both boxes do the same thing?

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