Ignition box retard with RPM

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yellow rose

yellow rose

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I finally have a chance to check some of the various ignition boxes I have on hand to see how they retard with RPM. At the moment I have a MP orange box, an early 1980's gold box, a Mallory HyFire IV, Mallory HyFire V, Mallory HyFire VI digital, and a Mallory HyFire VII analog.

Tonight I tested 3 of the boxes and these are the results.

Mallory HyFire VI digital box with a Mallory 29440 coil. Model number 685.
-1 degree at 3800 RPM
-2 degrees at 5000 RPM
-3 degrees at 7500 RPM

With this box, if you set your total of say 35 degrees at 3000 RPM, just 800 RPM's later you lose a degree. By 5000, you are at 33 total and at 7500 you'd be retarded back to 32 total.

Mallory HyFire V analog box with a Mallory 29440 coil. Model number 690.
-1 degree at 3500
-2 degrees at 4750
-3 degrees at 6200
-4 degrees at 7000

You can do the math.

Mallory HyFire VII analog box with a Mallory 28880 coil. Model number 667.
-1 degree at 4000 RPM
-2 degrees at 6000 RPM
-3 degrees at 7000 RPM
-4 degrees at 9500 RPM

Again, you can do the math and see the issue with locking out the timing, or not setting your total at max RPM.

I can test these boxes to 12,000 if I want to. The machine will easily go that high.
 
RustyRatRod said:
I'm curious about the orange box.
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I tested it but I didn't write that down. I'll do that one tomorrow and post it.

I also did that gold box and that thing lost ONE DEGREE in 10,000 RPM. I was stunned. That's pretty impressive considering what little I know for sure at this point.
 
j par said:
So if I don't hit the nitrous button till 9k I'm okay for a 200 shot...?
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That I'm not sure about. I don't have an MSD 6 here to test yet. I need to test the analog and digital.

I also need to test several boxes of the same model to see how much deviation there is across the same model.
 
built in nitrous retard....

"Most nitrous companies suggest retarding timing by 1.5-2.5 degrees per 50 hp of nitrous use. For example, a 200hp nitrous tune would require the timing to be retarded from 6 to 10 degrees. "

So the 690 box is good for a 100hp shot...stock. :lol:

could you advance your timing +4 and use a retard box at lower RPM's to compensate for the upper RPM lag?
 
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pishta said:
built in nitrous retard....

"Most nitrous companies suggest retarding timing by 1.5-2.5 degrees per 50 hp of nitrous use. For example, a 200hp nitrous tune would require the timing to be retarded from 6 to 10 degrees. "

So the 690 box is good for a 100hp shot...stock. :lol:
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Well I was thinking no matter what happened if I hit the nitrous at 9 k kablooey...
 
wonder what a stock box reads as well as a straight points distributor. One wonders if the TO-3 transistor in an ECU is rated to handle the higher speed switching of the other models (blue,red, chrome,gold)?
 
Just to be clear you are these are not adjustable NO2 retard boxes like the MSD digital 6 box wherein when you apply 12v to the retard circuit it retards the adjustable preset amount.

these are just straight timing boxes that retard the timing all on their own
 
Is the timing retard an intentional design element, or is it just a function of the speed of the box?

I don’t know much about the inner workings. Does any one have schematics?
 
roccodart440 said:
Just to be clear you are these are not adjustable NO2 retard boxes like the MSD digital 6 box wherein when you apply 12v to the retard circuit it retards the adjustable preset amount.

these are just straight timing boxes that retard the timing all on their own
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I know, I was just :poke:...:D..
9k then nitrous..:rolleyes:...
 
pishta said:
wonder what a stock box reads as well as a straight points distributor. One wonders if the TO-3 transistor in an ECU is rated to handle the higher speed switching of the other models (blue,red, chrome,gold)?
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I'll do a stock box soon.

Points do not retard with RPM. Neither does a Unilite. Well, it lost a degree at 10,000 but even with a pretty big coil it won't fire the plugs anywhere near that high up.
 
Mike69cuda said:
Is the timing retard an intentional design element, or is it just a function of the speed of the box?

I don’t know much about the inner workings. Does any one have schematics?
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It's called "slew rate" and its inherent in all ignition boxes. I'm not smart enough to say why one design has a better slew rate than another, but certainly it's quicker electronics. Don't forget...a timing light has a slew rate also. A cheaper light may not be as slow as a dial back. Or it could be.

That's why setting timing to a nominal value may not be what it really wants. The only way to really know what the engine wants is to test and look at the plugs. Always use the same light every time.
 
yellow rose said:
It's called "slew rate" and its inherent in all ignition boxes. I'm not smart enough to say why one design has a better slew rate than another, but certainly it's quicker electronics. Don't forget...a timing light has a slew rate also. A cheaper light may not be as slow as a dial back. Or it could be.

That's why setting timing to a nominal value may not be what it really wants. The only way to really know what the engine wants is to test and look at the plugs. Always use the same light every time.
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Thanks, that what I thought. A guy would think newer design boxes would be faster due to advancement in semiconductor technology, but maybe there other factors. Can really tell without a schematic.
 
Mike69cuda said:
Thanks, that what I thought. A guy would think newer design boxes would be faster due to advancement in semiconductor technology, but maybe there other factors. Can really tell without a schematic.
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I'm picking up a brand new, never been hooked up MSD digital box at the end of the month to test. So we'll see how that does.

I also have a Mallory HyFire VII digital box to test and see how that does.
 
yellow rose said:
I'm picking up a brand new, never been hooked up MSD digital box at the end of the month to test. So we'll see how that does.

I also have a Mallory HyFire VII digital box to test and see how that does.
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DIgital 6?
 
yellow rose said:
I think so. A member here has it and I'm going to grab it when I'm over there and test it.

Can't wait!!!
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Much appreciated

If you can with that one... test the accuracy of the straight timing and then test to see the accuracy of the built in NO2 retard.
 
pishta said:
wonder what a stock box reads as well as a straight points distributor. One wonders if the TO-3 transistor in an ECU is rated to handle the higher speed switching of the other models (blue,red, chrome,gold)?
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That's got to be a part of it. And why, with maybe exception of the NASCAR boxes, related to why they didn't recommend them for lower rpm and extended use. The RPM restriction probably relates to dwell and the ballast resistor-coil combination selected for best performance in Stock and SS class racing.

Mike69cuda said:
Is the timing retard an intentional design element, or is it just a function of the speed of the box?
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Like YR posted, its every switch takes time. It's everything. See this discussion at moparts
Mallory Unilite timing issue

and this post in particular on speedtalk.
drag race engine ignition systems - Don Terrill’s Speed-Talk

It really doesn't matter for street use because the engine is rarely anything more than 3000 rpm.
But as Tuner shows in that post, at 6000 rpm, each degree is .00002778 sec. So if the electronics delay adds up to just .00006 seconds - there's 3 degrees!

It also only really becomes an issue when people assume assume timing that is limited at 2500 rpm is going to be the same at 5500 rpm. Limiting the advance, especially limiting it early, is a loser for racers that need to max out the engines performance. Maybe in bracket racing its no biggie, but for stock eliminator it always is. That's who first clued me in this - a coworking who had SUN machine and ran stock eliminator. He didn't know the real reason, but he found out on the track that Direct Connection knew exactly what they were doing by installing a big secondary spring in the tach drive distributor.
(In the DC Bulletin it says is mechanical losses and my guess is that whoever wrote that at the time believed it)

Point is that if the distributor is curved for performance in the race rpms, then it doesn't matter what the box and pickup are doing. The distributor curve compensates for it; the spark plug gets fired when it does the most good and that's the end of. Hence some of those comments in the Speedtalk thread.

I don’t know much about the inner workings. Does any one have schematics?
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IIRC in the MTSC series there are some cutaways and general description. Nacho in Venezuela/Spain (hopefully the latter these days) has had some cut open and replaced transistors. He discussed it on moparts and Charger forums etc.

Kit Carlson could definately figure one out if he hasn't already done so.
Timing Light Accuracy

Mike69cuda said:
Thanks, that what I thought. A guy would think newer design boxes would be faster due to advancement in semiconductor technology, but maybe there other factors. Can really tell without a schematic.
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For the big companies we know what any advances are used for - they can be made cheaper and sold at higher price.
 
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a "high speed" transistor (1) has a turn on/hold/turn off time of 2.1u seconds or 2.1 microseconds (millionths of a second) so that should easily handle .000027xx per degree (that would be 27 microseconds) as it could theoretically do a complete off/on/off cycle in 1/10 of a degree at 6000 RPM, stack a few in series and then your slew rate is adding up . Honda motorcycles were doing 22000 RPMs using some sort of ignition back in 66 and 20K up to today.
This is probably close (minus LED status indicators) to an old Chrysler ECU coil driver schematic as it even notes a heatsink required for T2 (the T0-2 you see on top and ECU with the heat sink under it) S1 is a point breaker but could be triggered by a Hall effect or mag pickup with supporting components.
41A_1.jpg
 
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pishta said:
a "high speed" transistor (1) has a turn on/hold/turn off time of 2.1u seconds or 2.1 microseconds (millionths of a second) so that should easily handle .000027xx per degree (that would be 27 microseconds) as it could theoretically do a complete off/on/off cycle in 1/10 of a degree at 6000 RPM, stack a few in series and then your slew rate is adding up . Honda motorcycles were doing 22000 RPMs using some sort of ignition back in 66 and 20K up to today.
This is probably close (minus LED status indicators) to an old Chrysler ECU coil driver schematic as it even notes a heatsink required for T2 (the T0-2 you see on top and ECU with the heat sink under it) S1 is a point breaker but could be triggered by a Hall effect or mag pickup with supporting components.
View attachment 1715470460
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In 1966 the Honda would have had points wouldn't it? Unless Honda was testing electronics.
 
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