MP Dist Timing Scatter and Bad Curve

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Rice Nuker

Rice Nuker

Let the Coal Roll!
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I just read that the MP dist from 99 to current has a rapid and long advance curve and it has light weights and springs which allows for timing scatter the entire time it is not at full close or full open. Says cannot be fixed as is inherent in design.

Anyone have technical feedback regarding this info?

I read it in "Mopar Action FEB 2014" (says that on cover).
 
All I can say is someone with a good distributor machine, or a scope with logging and a secondary timing reference knows.

I know about the OEM electronic, not so good either, but few know or care. For most it just adds a bit of character to the tone of an engine.

I like optical, or Hall vane sensing. Variable reluctance sensing is not recomenned for position sensing in the motion control industry. There are inherent errors in timing related to RPM, runout, and remenant magnetism.
 
I think the $45 HEI distributor has a better pickup design. Similar to GM's "small cap" and later Ford distributors, it has multiple pickup fingers all around the reluctor. It seems that would correct for any shaft wobble. Many on here state "Chinese junk", with no basis. As a proud American, I can say that U.S. junk can compete with the best Chinese junk, and much of ours has fancy after-market labels and high prices. Our genius is in marketing junk to the world. If the Chinese were as smart, their stuff would be red (like MSD) or yellow (like Accel).
 
So, variable reluctance sensing does include EDIS and old moper EI because of the same magnetic (excluding the transistorized side) process for detection of passing teeth?

Interesting. Are you saying that the resultant timing jitter is caused by inherent properties in the magnetic trigger (and possibly the poor resolution of the mopar wheel due to the number of teeth) rather than the Mopar weight - spring mechanism?

I'm pretty well shot here so I am just guessing.

Anyway, the article appears to imply that the hysteresis is in the mechanical advance parts as they "spring" around randomly jittering the timing while averaging a timing curve. I guess.

What do yall think?

:)


KitCarlson said:
All I can say is someone with a good distributor machine, or a scope with logging and a secondary timing reference knows.

I know about the OEM electronic, not so good either, but few know or care. For most it just adds a bit of character to the tone of an engine.

I like optical, or Hall vane sensing. Variable reluctance sensing is not recomenned for position sensing in the motion control industry. There are inherent errors in timing related to RPM, runout, and remenant magnetism.
Click to expand...
 
Variable reluctance works by a change in magnetic field, generating a voltage. The pick up sensor is a coil on a magnetic pole. When the tooth of the reluctor comes in proximity of the sensor pole, it changes the flux in magnetic circuit. The voltage generated is proportional to the change in flux. The electronics interprets the waveform, it first must go negative, then pass zero and then triggers at a positive threashold. The threashold point happens earlier with increasing RPM because the sensor voltage increases. Variations in the magnetic, due to runout and remnant magnitizm changes, timing on a cylinder by cylinder basis.

What I am saying is not only based on physics of the situation, but also verified on NOS, MOPAR distributors using electronic equipment. I basically capture the tigger points then measure the timings.

How much error? A few degrees. It makes a difference to me.

For those with a degree wheel, and timing light, cylinder firings are 90 degrees apart at the crank for V8.
 
WTH is "timing scatter"? Sounds like a made up term to make you go out and buy another distributor. What exactly does that mean?
 
Rice Nuker said:
I just read that the MP dist from 99 to current has a rapid and long advance curve and it has light weights and springs which allows for timing scatter the entire time it is not at full close or full open. Says cannot be fixed as is inherent in design.

I read it in "Mopar Action FEB 2014" (says that on cover).
Click to expand...

I'm not sure with the words "Fast and Long" because fast is short and long is slow"
The MP distributor and any like it in the old school fashion have this problem because of light weight springs. When the engine slows down or speeds up, the springs will expand and contract. This is a problem for street engines running a race distributor and will always be so.

The big problem is not so much the distributor by the end user. To many people use the MP high performance distributor as a street part with disregard to its original intent while demanding the max power from there engines. Which may not be so sweet on the street.

MP does have a spring kit (or used to, IDK any more) that provided the end user with a few sets of springs to swap in and mix up to vary the curve advance. While the spring kit helps a bunch, the "Mechanical" limitations of a spring and weights are something that will be ever present.

Programable distributors are the way to go now and should be seriously considered for a powerful engine. Street or strip. There pricey and worth every last penny since they will out perform the old school stuff hands down and by a huge margin.

If it is possible, combine it with a multi spark ignition, if so not all ready equipped with it.
 
..i purchased the Mopar Performance Mallory unit in '09 along with the spring kit.
i have had no problems with it and with the kit and it's built in adjustability the curves and rates are limitless...a great way to learn.
 
Timing scatter to me means a variation in timing between cylinders. An example is on a V8 #1 is at 14 ° BTDC, but #6 is 16° BTDC. But how many take the time to look? Looking can be done on each cylinder, each cylinder 90° apart in firing order. Stable timing is also requried.

If a feeler gauge is used to check pickup gap, often there is a small variance between teeth gaps. The result is a small variance in timing. If a scope is used to view the pickup signal, amplitude varies in a rhythmic way, and so does timing. Spark scatter is a reason why an engine seems to ping on one cylinder first. I am sure some slant six owners have discovered that with worn distributor bushings, due to side load of drive gear.

Distributors can be optimized by reworking, or re-engineered an example is a Mallory.

Crank and sensor in most late model cars are quite good, and the engines are smooth. The same is possible, with old iron, with proper injection and ignition.

I stick with my story, few care, timing variations add character to the sound of an engine.
 
If that's the case, then you will never get it out unless you index the crank. Over and out, roger wilco.

Thanks for splainin it.

KitCarlson said:
Timing scatter to me means a variation in timing between cylinders. An example is on a V8 #1 is at 14 ° BTDC, but #6 is 16° BTDC. But how many take the time to look? Looking can be done on each cylinder, each cylinder 90° apart in firing order. Stable timing is also requried.

If a feeler gauge is used to check pickup gap, often there is a small variance between teeth gaps. The result is a small variance in timing. If a scope is used to view the pickup signal, amplitude varies in a rhythmic way, and so does timing. Spark scatter is a reason why an engine seems to ping on one cylinder first. I am sure some slant six owners have discovered that with worn distributor bushings, due to side load of drive gear.

Distributors can be optimized by reworking, or re-engineered an example is a Mallory.

Crank and sensor in most late model cars are quite good, and the engines are smooth. The same is possible, with old iron, with proper injection and ignition.

I stick with my story, few care, timing variations add character to the sound of an engine.
Click to expand...
 
KitCarlson said:
If a feeler gauge is used to check pickup gap, often there is a small variance between teeth gaps. The result is a small variance in timing. If a scope is used to view the pickup signal, amplitude varies in a rhythmic way, and so does timing. Spark scatter is a reason why an engine seems to ping on one cylinder first. I am sure some slant six owners have discovered that with worn distributor bushings, due to side load of drive gear.
.
Click to expand...

This is the kind of doings that make some people faster than others. The attention to detail. However as stated above crankshaft indexing would be in order also.

As stated above, interesting thread.
 
RustyRatRod said:
If that's the case, then you will never get it out unless you index the crank. Over and out, roger wilco.

Thanks for splainin it.
Click to expand...

It is not about an offset, but about phase errors between ignition events. A good distributor machine is better, it reduces the timing drive errors in chain and gears. It also regulates RPM more precisely. I settle with spinning the distributor shaft with a large drill press, and sorting it out using a micro controller, to measure ignition tiggers in a precise way. For that stable rotation is necessary. But a timing light and degree wheel works for the masses. For a slant six the ignition events should be 120 degrees apart.

Attention to detail. Accurate machining, balancing, cc chambers, accuarate ignition and EFI. Internal combustion engines can run sweet, smooth and powerful. But many seem impressed by those that sputter, miss, pop, rattle, ping and smell foul. Yeah, I go to car shows when time permits.
 
Nice explanation Kit.

RustyRatRod said:
If that's the case, then you will never get it out unless you index the crank. Over and out, roger wilco.

Thanks for splainin it.
Click to expand...

Well, that would help some but it is not the major problem to the issue. The distributor has its own issues. Then there is the joints between that and the cam. Distributor gear and timing chain. The cam itself. Absolute rod and piston length/height.
 
KitCarlson said:
Timing scatter to me means a variation in timing between cylinders. .
Click to expand...

Might be a difference in terminology, but to me it's much broader than that, to me it's poor timing control in general

Anybody who's see a few cars / distributors on tune up machines can attest that Mopar timing drives from end to end "aint that great."

I don't run one (yet) but there's no doubt that Mopars are ONE family that can certainly benefit from crank triggered systems.

I know this will "spark" comments, but most of the GM V8 distributors are MUCH better than the Mopar stuff. This doesn't mean they don't wear out

The whole "end to end" distributor drive in a Mopar is pretty crude, in some ways. Possible variations in the block bushing for the intermediate shaft, as well as the flat tang drive--probably the poorest coupling design that could be conceived.

You can't even buy 'em anymore, but when I had my first (69 RR) I used to always have a spare package of distributor shaft bushings which came in a kit

I thought I was in heaven when I scored a hemi, tach drive, dual point one day. They have a ball bearing top bearing, and help stabilize spark "in their day."
 
rumblefish360 said:
Nice explanation Kit.



Well, that would help some but it is not the major problem to the issue. The distributor has its own issues. Then there is the joints between that and the cam. Distributor gear and timing chain. The cam itself. Absolute rod and piston length/height.
Click to expand...

Of course not. Why did I even say a frikkin word? I guess I'll learn one day.
 
The fast and long thing is that the advance curve rate is high and the total advance in the system is a long travel as well. Just reiterating what they said and what they mean. No clue if they know what they're talking about. Which is why I started the thread. Good info on here so far!

Also it sounded like they were implying that the advance weights were rattling round or springing around causing variances in the timing until the mechanism had bottomed out at full advance or the other end at min advance.
 
I think the problem with those 99 and up units were that the weights were to light and that made them hard to control.
 
Nuker,

1st post. Oh Ok. Makes sense.

2nd post to Bobby. Agreed!
 
RustyRatRod said:
Of course not. Why did I even say a frikkin word? I guess I'll learn one day.
Click to expand...

Calm down, will ya? Every time one of us posts, we are not personally attacking you.

I think Rumble was just pointing out what might be termed bigger issues.
 
So. Does anyone have recommendations for improving the function of the MP dist?
I have a fairly new SB unit and would like to have it operate as well as possible.

Should I just chuck mine at a tree from a moving vehicle? :_)
 
Well I think from the discussion above the first order of business is to find out if it's actually the distributor, or some other problem. I admit, determining that might be a trick.

Some of what you can try...............

Try to round up a lean burn dist which will have locked mechanical advance, no vacuum, and the pickup coil(s) will be solidly mounted. Make some temporary tests with that to see if the problem improves.

If it does, don't jump to conclusions. Pull the dist. gear and attempt to determine the condition of the intermediate shaft bushing. Also while you have the gear out, examine it generally for wear / damage, and compare the two distributor shafts "fit" into the drive tang on the gear.

If you can round up "a buddy" with a distributor machine, that would be a great asset. However, you have to take that "with a grain of salt" because if the problem happened to be say, a combination of cam drive/ dist gear and the distributor itself, a "run" on the machine might convince you that it's a distributor problem. Stabbing a new distributor in might be disappointing in that case.

Or, LOL, you can just convert it to a crank trigger
 
Nice, 67.

Based on the single source of reference, I figure my distributor has floppy weights and behaves mildly irregular from the factory. I have no testing equipment to verify that this alleged "timing scatter" is isolated to the distributor or said mechanical advance system.
What I'd be lookin for is any retro-fits or solutions to said timing scatter. Preemptive fix is what I'm looking for, as the engine is awaiting a rebuild.

Long term, I am reasonably confident that i'd like to run edis and megasquirt, but that could take another 5-23 years at the rate I'm going.
 
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