A few observations from both working on, and being on the team that developed the GM coil in cap HEI's, decades ago.

The MSD "curve kit" shown, and others that are configured as same, ARE NOT FOR STREET USE. They are for drag racing, where initial will want to be jacked to the moon over a reasonable street setup. They normally deliver 12 crankshaft degrees of timing, and are designed to eliminate the vacuum advance from the timing equation. Once again, these kits are not for street use, only drag racing, with no vacuum advance in use.

Stock GM coil in cap HEi's have options, as in literally, YES< 437 different advance curve parameters for all the weights/center combinations. Finding one that actually works is a trial and error, error, error situation. The ONLY pair that is well documented is later truck/suburban/crate engine and ZZ series package weights 41, center 375. This package gives 22 crankshaft degrees.

Contrary to urban MYTH and outright lie, the "slots" shown that pass through the plate ARE NOT start/limit plates, as the point distributors use, they are simply large enough to allow the free movement of ALL 437 different curve combo's, without interference. MANY, way too many people advise welding them up, adding screws, all sorts of "fixes" to tailor start/limit areas to weight and cente4r sets that just do not work. Simply stated, EACH different weight/center set has in it, three parameters, the actual curve plot, from start to limit, the START point, and the LIMIT point. IF the start point, curve are correct for what you want, and the limit is too high, or low, you have the wrong weight/center configuration, go forth and test, test, test with different combo's, or listen to all the people that insist on NOT doing it right, by jamming screws into, welding up, and other "methods" of creating all sorts of continuing problems with start, limit and curve problems.

MOST of the better aftermarket large HEI's now have adopted the ZZ 41 weights and 375 center package, BECAUSE IT WORKS IN ALMOST EVERY APPLICATION. Only the most radical engines can't use that much curve degrees, and need less curve degrees, along with jacked to the moon initial, and don't make enough vacuum to run a vacuum advance,m not even the Crane adjustable, that works the best, all the way down to 4 in/hg vacuum. Other adjustable vacuum advances don't work lower than 7 to 8 in/hg vacuum.

As far as a vacuum advance degrees stop, the MSD is not even close to a fair one, it pales in comparison to ease of use, and adjustment to the Crane 99619-1 stand alone scroll plate, BUT, Crane does not mount the plate in the correct place on the advance. MSD's stop will work on the end screw, the Crane should be placed on the DIAPHRAGM side of the pull pin, with a single 8/32 threaded hole, drilled and tapped into the vacuum advance mounting bar. then, the Crane stop does the same as the MSD does, stops the pin as it travels into adding timing, without adversely effecting vacuum pull adjustment. In fact, the Crane stop has adjustment in 2 crankshaft degree increments, not just the 4 MSD stops. the Crane adjusts with a single screw loosening, change the stop position, tighten the screw, no taking it off, flipping it up side down, backwards, as the MSD requires.

Once installed, the Crane delivers 10 separate degrees adjustments, along with completely locking out the vacuum advance completely, in one easy to use device. And, it can be used on stock GM type, non-adjustable vacuum advances as easily as it is used on all adjustable ones. Drill one hole, tap it, install the plate, a machine screw and flat washer, trim the excess threads off the screw on the underside of the vacuum advance mounting plate so they don't hit the distributor body and hold the mount plate up, and adjust it as you see fit...done. Change it, loosen the screw, move the plate, tighten the screw, done.

Both the Crane, AND MSD stops do good, in that they separate the degrees adjustment form the vacuum adjustment, or rating on a stock advance, from each other, exactly the way it should be. The Crane just does it for far less money, and is considerably further adjustable than the MSD is, and, mounts very easily with drill, tap, cut excess threads down, done.

Please be aware, I AM NOT knocking the info given above, it is good in so many areas that others have managed to make so muddy and unclear. But, over many years of working on fixing all sorts of different "methods" that just do not work on these distributors, I have seen so many "variations" on coming close to doing it right, from screws, welding, even very close to "mount the distributor up side down in the engine", it isn't even close to funny.

Regarding engines that like excessive timing, in the early days, they would have had distributors like the old Corvette, no vacuum advance, 18 degrees of initial timing, with another 18 degrees of mechanical curve, and variations close to that, because the cams were so radical, with intake valve closing points way far into the piston rise, they literally caused serious mixture reversion up the inlet ports, they needed the CRUTCH of way too high ignition timing, and too low a vacuum level from excessive late intake closing mixture reversion.

 

Dave,
Thank you for your input. I based a lot of what I did on information I learned from you and others. I agree with everything you stated about the slots under the centerplate (as evident by the photos I posted).
As I mentioned in my original post, I have been searching for the GM #375 centerplate and #41 weights as you have recommended... I just have not had any luck finding them and was looking for some other alternatives.

On previous posts, I believe you mentioned that you had a distributor machine that could measure a distributor's mechanical advance and advance curves. I encourage you to test the MSD 8428 kit installed in an HEI with light/medium weight advance springs... I am not sure when you tested the MSD 8428 kit and only got 12 degrees of crankshaft advance. I got 20 degrees of crankshaft advance from this kit when using the methods described in my post. My initial timing was 18 degrees, and my total mechanical advance 38 degrees at the crankshaft. Maybe MSD update their kit.
I am running a larger duration cam (242 degrees dur @ .050), so that is why I set my initial at 18 degrees. I am also getting 14 Hg of vacuum at idle.

I agree, that the MSD vacuum advance limiter was a few more dollars then the crane vacuum advance limiter plate, and the crane limiter plate was a lot more adjustable... but it was much easier for me to install the MSD vacuum advance limiter and it provided the desired results.

The main purpose of my post was to inform others that they should not assume their advance weights and/or centerplate on a brand new aftermarket GM Style HEI were installed correctly at the factory. Mine was not, and I did not realize this for several years.

It was because of some of your previous post that inspired me to learn more about how my HEI functioned.... and for that I thank you!

 

UPDATE:
After thinking about Dave Ray’s comments, I wanted to double check my timing results… and this time I videoed the timing process.
It seems that the truth is somewhere in between my original timing results of 20 degrees of mechanical advance, and Dave Rays comment that the MSD 8428 advance curve kit would only provide about 12 degrees of mechanical advance.

After reviewing “Freeze Frames” from the timing video, it appears that I am only getting about 16 - 17 degrees of mechanical advance (I guess my old eyes aren’t what they used to be :nerd.

Below are some screen shots taken from the timing video of Initial Timing at 850 RPM (18.5 degrees), and Full Mechanical at 3500 RPM (35 degrees).

Initial Timing at 850 RPM (18.5 degrees)

Full Mechanical at 3500 RPM (35 degrees)

I have also updated the results of my timing curve with the MSD 8428 weights and centerplate with the light weight + medium weight springs installed.

850 RPM (Idle) - 18.5 degree Initial
1000 RPM – 23 degrees
1500 RPM – 27 degrees
2000 RPM – 30 degrees
2500 RPM – 32 degrees
3000 RPM – 34 degrees
3500 RPM – 35 degrees
4000 RPM – 35 degrees
4500 RPM – 35 degrees
5000 RPM – 35 degrees

I am going to leave things as is for now, and may experiment with the silver "GM Copy" weights and centerplate in the future. If I change anything, I will keep everyone posted.

 

I have 5 distributor machines in my shop, and a 2.5K psi run pressure tester to run test the ignition systems after I complete the conversions to them.

I never intended for you to feel anything adverse from my post. You did great work, and even in your update.

A few things that are vitally important for the regular HEI:

The point distributors had significantly different slot lengths and bushings to match the engines they were used in. The curve degrees were mostly in the curvature of the center welded to the distributor shaft, and to change a curve, one needed to select the correct slot length, curvature, stop busing, and springs.

One of the "updates" we devised for the large HEI was the long slot length for ALL the distributors, and to put the start and limit points into the actual curvature of the center plate. Since we were aware of so many different specifications for various emissions profiles for so many different GM makes and engine/emissions configurations, the slots were set up do that ANY and ALL curvature/weight configurations would install in ANY distributor, and when turned one way, or the other work for a right, or left hand rotation distributor.

That is where the issues come where some insist on stopping down the slot lengths to change start/limit points. If it doesn't start/limit in the right places, you AIN'T got the right profiles package of weights/center.

Also, ABSOLUTELY ESSENTIAL TO KNOW, large regular HEI's ARE NOT FEEDBACK types, they do not time using a computer. Here is where I get lambasted on this subject. IF THE HEI HAS MECHANICAL AND/OR VACUUM ADVANCES, DO NOT USE A "DIAL BACK" FEATURE ON A TIMING LIGHT TO SET, READ, RECORD A CURVE, NOR SET TIMING, NO MATTER WHOM SAYS DIFFERENT.

A dial back feature is ONLY for feedback, electronically timed ignition systems on fully computerized engines, such as ones that use Electronic Fuel Injection systems. Dial back is an electronic computation feature that figures timing milliseconds past when a regular system would report a firing event, to give the computer the "lead/lag time" to actually compute the timing event, after receiving and processing the various input information, such as engine heat, throttle position, exhaust oxygen level, etc.

When a dial back feature is used on a direct input system, one with mechanical/vacuum advance, the lag time still exists, and the timing report will be incorrect because of the lag time of the dial back feature. To do a regular system the right way, do what is shown above, degree the balancer, leave the dial back off, and go that route.

We will still have to find time, possibly during the winter snow time, to get into just why we need timing advance curves for our engines. It should be an excellent discussion.

 

I never intended for you to feel anything adverse from my post. You did great work, and even in your update.

Hello Dave,
No adverse feelings at all… as I always welcome (and value) your feedback!
I did have a question. I wanted to get your opinion on the modification shown below.

I did read that the centerplate can be modified to gain a few more degrees of mechanical timing.
I was thinking about removing a very small portion of the centerplate (as identified by the red highlights and arrows shown in the photo below).

I would make a template so the modifications would be consistent on both sides of the centerplate. I am only looking to gain 1½ to 2 distributor degrees of mechanical advance (3 to 4 crankshaft degrees), so it seems that very little material would need to be removed. At the centerplate’s present position, there is still about 10 degrees of centerplate pin rotation in the counterclockwise direction before the pins would hit the end of the pin slots. The modification would only move the pins 2 degrees counterclockwise… thereby still leaving both pins within the slots, and the centerplate and weights would still control the start/stop points of the mechanical advance.

It also appears this modification would not affect the timing curve too much, because once you start to gain mechanical advance… the modified portion of the centerplate would no longer be in contact with weights (see photo below).

Since I have never done this before, I wanted to ask if the procedure shown above would work for my desired goals.

 

Cutting the area in the first picture changes the start point of the curve.

Cutting back the tips of the weights in the second photo increases both degrees, and speed of top rpm advance limit point doing what you are trying to accomplish. A simple, subtle arc of metal removal goes a long way, so, do a very short cut, test, cut, test, you'll get the hang of it. It is all just simple trial and error.

I use an upright standing bench style belt sander to "tip the end arcs" of the push bars on the weights, and between them, I simply use the same 'sound and time length of cut' for each weight during my cuts. I have been doing it for decades, and from that experience, they come out virtually the same, but, to the novice cutter, do one, lay it on top of the other, cut to match.

 

Dave, Thanks for the feedback!
I was planning to modify the centerplate by changing the starting point of the curve as you mentioned.... thereby gaining a few degrees of "overall" mechanical advance.
For example:
If I am currently at 18 degrees initial and 35 degrees total mechanical @ 3500 RPM, that is 17 degrees of mechanical advance with the current MSD kit.
If I change the starting point to 15 degrees initial (by removing some of the centerplate material (as shown in the top photo) but my total mechanical still stays at 35 degrees at the same 3500 RPM, I will now have 20 degrees of mechanical advance from the "modified" MSD kit.
Then I would just adjust my distributor to increase my initial timing back to 18 degrees, and my total mechanical would now be 38 degrees at the same 3500 RPM.

I did not want to adjust the tips of the weights to gain mechanical advance because (as you mentioned) that would also increase the RPM that the total mechanical advance would be seen.
I know I could install lighter advance springs to help compensate for this scenario, but I noticed that when the lighter springs are installed with these weights... I start to get some mechanical advance coming in at idle (and that is something I am trying to avoid doing).

As you also noted, I plan to work slowly and just make very small adjustments at a time... test.... and readjust as needed. To be honest, it takes me more time to set-up and photograph this process than the time it takes me to do the adjustments!

Thanks again for all of your guidance!... and I will keep everyone posted of the results.

P.S. I look forward to your future post of the reasons why we need timing advance curves for our engines. I always enjoy learning something new!

 

If you cut the start end of the center plate, realize you will need heavier springs to keep the "variable (hunting) idle" out of the equation.

To get the same IDLE timing, after stopping down the INITIAL, you'd also have to re-adjust the degree stop plate for the degrees difference between first and revised INITIAL timing. MSD is still very workable, Crane a lot easier for those that want to use one.

See now why I like to get as many adjustment features into something as I possibly can, I want EVERYTHING to 'play with".

As a forward to the future timing topic, everybody start thinking about why we need advanced timing in the first place, there are about a hundred factors in play, and we will get to just about all of them in that topic.

 

Dave,
Thanks for the additional information on the possible "domino effect" items once the start position on the centerplate is adjusted. I do have an assortment of advance springs for this purpose.... if needed.

After spending some time reviewing the photos I took of the various weights and centerplates, I think I'm going to be ok with minimal adjustments/changes to my current set-up after I modify the MSD centerplate.

BUT, I certainly know what items to pay attention to... thanks to your heads-up!
I'll keep you posted, and thanks again for all of your help!

 

NEW UPDATE – MSD Centerplate Modified:
I wanted to provide everyone with the results of modifying the MSD 8428 centerplate (as referenced in my previous posts). I’ll provide the results first, and then follow up with the details taken to modify the centerplate… for those that are interested.

By reviewing the previous initial timing (18.5°) and full mechanical (35°), I calculated that I was only getting 16.25° of mechanical advance from the unmodified MSD 8428 Advance Curve Kit. My goal was to achieve 20° of mechanical advance from the MSD kit. After the centerplate of the MSD kit was modified to adjust the starting point of the timing curve, I was able to get 20° mechanical advance.

After the MSD weights and modified centerplate was reinstalled, I readjusted my initial timing for 16° @ 850 RPM (no vacuum advance)… and my new total mechanical advance was 36°@ 3300-3500 RPM. I did not need to change the advance springs from my previous set-up. I also did not experience any “idle hunting” while in drive (850 RPM), or in park (1000 RPM) since my mechanical timing did not start to advance until 1200-1300 RPM.

I chose to use the 36° total mechanical advance because I read that many people using the AFR 195 aluminum heads (with similar engine builds) liked this setting. A few liked 38° total mechanical advance. The next time I go to the track, I will compare my ¼ mile MPH between the different settings.

I once again videoed the timing curve of my engine after the MSD centerplate modification was completed. By viewing the “Freeze Frames” from the video, I am able to see the timing marks much easier and more accurately. The photos also verify the results achieved.

Initial Timing at 850 RPM (16 degrees)

Full Mechanical at 3500 RPM (36 degrees)

Just a quick note about the advance springs I used. I used the light and medium tension springs (silver and blue) that originally came with the Pertronix HEI. I did not use any of the advance springs that came with the MSD 8428 advance kit. The wire used on the MSD copper springs (lightest tension) was so thin, that the circular loops at the ends of the springs started to open up just by installing these springs onto the centerplate and advance weight pins. My guess is that these copper color springs would begin to stretch (and loose tension) over time. I also did not use the MSD silver springs (medium tension) because they seemed to provide more tension then the medium weight spring I used from the Pertonix distributor. And the MSD strongest tension advance springs (blue)… were ridiculously tight. I only used these springs to confirm my initial mechanical advance setting.

I have also updated the results of my timing curve with the MSD 8428 weights and modified centerplate with the light weight + medium weight springs installed (with no vacuum advance).

850 RPM (Idle) - 16 degree Initial
1000 RPM – 16 degrees
1500 RPM – 28 degrees
2000 RPM – 31 degrees
2500 RPM – 33 degrees
3000 RPM – 35 degrees
3500 RPM – 36 degrees
4000 RPM – 36 degrees
4500 RPM – 36 degrees
5000 RPM – 36 degrees

My mechanical advance is coming in quickly at the lower RPMs, which works pretty good for my set-up (411 gears with a 2004R Trans with a 2800 stall converter).

With the vacuum advance connected connect to a “Full Time” vacuum port, my initial advance was now 27°… so my vacuum advance was adding 11° of advance with the MSD stop plate still installed in the “D” position. No change was needed to the MSD stop plate from my previous set-up.

Initial Timing plus vacuum advance connected at 850 RPM (27 degrees)
My “All in” Total Advance with vacuum advance connected was now 47°.

For those that are interested, below are the details of how I modified the MSD 8428 centerplate to achieve my goal of 20° of mechanical advance at the crankshaft. I approached this project a little differently (as you will see in my procedures below). I wanted to see if I could apply some logic and math to try and achieve the desired results without several attempts of modifying the centerplate, followed by “in vehicle” testing. I am not saying that this is the correct way to do this, but it worked for me with the tools I had (or made). I was able to get the adjustment I wanted on the first try… Maybe I just got lucky!

I placed the distributor in a vise, and locked the distributor gear from moving. I installed the degree template as shown (image of a protractor copied from the internet onto a word doc, proportioned to the correct size, printed, and taped to a piece of cardboard), and taped a brake cleaner spray can tube to one of the rotor arms as a pointer. I also inserted a push pin into the end of the red tube and cut the head off for a more precise pointer.

I started by installing the unmodified MSD centerplate and weights into the distributor (placed at the start position of the advance curve), and set the pointer to 90° and locked the template in place to keep it from moving.
From this point forward, it is extremely important that you do not move the pointer (as attached to the rotor arm) or the degree template once you begin to modify the centerplate.

As you can see in the photo below, I placed some masking tape onto both ends of the centerplate, so I could mark the contact points between the centerplate and the arms on the weights at the “start position” of the advance curve. These marks would be used as a guide when removing material from the centerplate to change the start position.

Since I do not own an upright belt sander or a bench grinder, I made my own version using a drill with a small grinding wheel, plus some flooring tiles to use as a work surface to modify the centerplate.

Once the correct work surface height was determined by stacking flooring tiles, the tiles were held in place on the workbench with a “C” clamp. A clamp light also helps brighten to work area.

Grind one side at a time and check movement on the distributor set-up. Since I needed 3.75° of additional advance at the crankshaft… that would equate to changing the start position of the advance curve to about 1.9°. Grind slowly, as very little material will need to be removed from the centerplate. Do not hold the centerplate in one position while grinding, as it is better to use an “arching” movement that follows the shape of the advance curve on the centerplate. As you get close to the final adjustment to the centerplate, finish removing the material with a metal file, and final smoothing of the adjusted portion should be done with a piece of emery cloth.

Final adjustment to one side of centerplate.

Once I finished adjusting one side of the centerplate, I attached some tan masking tape to the cover the compete surface of the centerplate and trimmed the masking tape to fit around the centerplate. I then removed the masking tape and turned the masking tape 180 degree and carefully attached the tape to the opposite side of the centerplate, so I was able to duplicate the adjustment to the other side of the centerplate. I used masking tape, but I think any method of “template transfer” would work.

As you can see in the above photo, the portion of the centerplate that is not covered is the amount that will need to be removed for about a 2° change in the distributor’s advance curve starting position (which is equal to 4° additional advance at the crankshaft). Notice the minimal amount of material that needs to be removed from the centerplate.

Once you are satisfied with the position of the masking tape, remove a portion of the tape so that you are able to R&R the centerplate from the distributor pins as you are checking the amount of movement on the distributor set-up. As you are finalizing the adjustment of the second side of the centerplate, use a file to remove enough material so that all play is removed between the weight arms and the centerplate with both weights installed… and positioned at the start of the advance curve. When you are “very close” to removing all play between weight arms and centerplate with a file, finish the modified edge with emery cloth to achieve a smooth surface for final fitment with no play.

Below is a photo of the finished adjustment to both sides of the MSD centerplate, and checked on the distributor set-up. Also note that the centerplate and weights are still controlling the starting and stopping points of the mechanical advance. The centerplate pins still move freely within the slots underneath the centerplate.

IMPORTANT NOTE: While this technique worked for determining the amount of adjustment needed to change the starting point of the advance curve, it DOES NOT work to determine the amount of total mechanical advance. When I used this method and moved the weights to their full advance position, I noticed 12° of distributor mechanical advance prior to modifying the MSD centerplate. That should have equaled 24° of crankshaft mechanical advance. As stated above, I only got 16.25° when testing in the car… so there must be some physics involved with the movement of the spinning mechanical advance mechanism that is way beyond my comprehension level. My guess is that this is why the MSD 8428 advance kit is stated to achieve 24° of mechanical advance (as shown in the instructions enclosed with the MSD kit).

Below is a photo of how I wrapped my distributor with paper towels while removing and installing the centerplate pin clips. Even with a magnet in place, these clips will sometimes go flying out when removed. It is also a good idea to cover the carburetor during this procedure.

I’ve learned a ton of information about the GM HEI while undertaking this project, and just wanted to share my experience.

 

If the weight pins use E clips, trim the bushings, and install, use the E clips.

You have done EXCELLENT work, sir. GOOD ON YOU. I am glad you are getting this dialed in to what works for your engine. And, you are seeing for yourself what it takes to get it dialed in. If you ever come this way for a vacation, come on by and hang out in the shop for a day.

 

Thanks Dave!
If I am ever in your area, I will give you a heads-up. I would love to see your shop.

The Pertronix HEI does not have the grooved recesses in the weight pins for the E Clips to be installed. These distributors are put together with the taller weight bushing from the factory. These are the same type of bushing that come with the MSD 8428 advance kit.

It is just an opinion, but I like the taller weight bushings with no E Clips vs the shorter bushings with the E Clips. With the taller bushings installed, the advance springs acts like the E clip... since the top of the taller weight bushing sits just underneath the the spring.

I also feel that the taller weight bushings would have less wear over time as compared to the shorter weight bushings (since there is more surface area of the bushing that contacts the weight pin).
I really don't have anything to back this up... it's just a gut feeling.

There are some aftermarket GM type HEIs (MSD Streetfire) that do not even use any weight bushings (take a close look at the original GM style silver weights and centerplate photos I posted). They just install the weights onto the pins, and the weight are held in place with E Clips. I think it is only a matter of time before the pin holes in the weights start to open up due to metal on metal contact/wear.
I have a set of these types of GM Style weights (from my spare HEI), and I am going to drill the pin holes out to except the weight bushings that come with most of the aftermarket HEI advance kits. If this works, I will probably post my results... since that would be an option for those that have these types of HEI advance weights, and are experiencing some erratic timing due to "weight wobble" (or just want to fix this issue before it becomes a problem).

Once again Dave, I wanted to thank you for your posts, and giving me the inspiration to learn everything I could about how the GM style HEIs function. I wanted to document my project from start to finish because there is so much misleading information... and several unfinished threads about these types of distributors on the web.

 

To RifRaf
Sorry if it’s bad to latch onto an old thread, but this seems my best route. 66-yr-old retired mechanical engineer finally has time to tinker. This thread between RifRaf and dave ray is AWESOME and WAY, WAY beyond anything I’ll ever do. But, I hit it in one of my MANY searches.

Back to the simple stuff… I’m hitting the confusion regarding HEI weights. I bought a PerTronix D8000 kit including the D9001 advance curve kit. The parts and photos of this kit are EXACTLY like RifRaf’s provided photo of the MSD 8428 kit. The PerTronix instructions show the centerplate being installed upside-down as compared to the MSD instructions and installed photo.

I called PerTronix to ask about any discussions regarding the conflicting directions. All news to him. As their directions show, he said the small tails on the weights need to fit into the recesses in the centerplate at full advance.
I called MSD. All news to that guy. As their directions show, he said the large end of the weights need to fit into the recesses in the centerplate when relaxed.

So, 2 questions to RifRaf:

• In your first entry, you described the problems you were having but said all was as originally installed by PerTronix 10 years earlier? You just never had reason to attempt addressing the problems until 10 years into it? Maybe never knew you had a problem?
• Did you ever run across any explanations that recognized the PerTronix way is seemingly wrong based on your experience? The latest PerTronix instructions show the same thing and tech support guy says the same thing. Boggles the mind to think they’ve been wrong for 10 years.

I did mention to both that the kits, seeming to be absolutely identical, are probably made by someone for both PerTronix and MSD. I said that to both companies and got no reaction. This is all very surprising to me. And I must admit, I’m not smart enough to appreciate the full implications of positioning the centerplate one way versus the other.

If this catches up to you or anyone with comments to add, it’d be much appreciated. Lacking that, I guess I’ll install the PerTronix parts the way MSD says to. THANKS much!

Here’s the orientation from PerTronix… just like “Incorrect Installation of MSD Kit” provided above.

 

In your first entry, you described the problems you were having but said all was as originally installed by PerTronix 10 years earlier? You just never had reason to attempt addressing the problems until 10 years into it? Maybe never knew you had a problem?

Prior to this project, I always noticed that when trying to set my initial timing, the timing mark at idle was VERY jumpy and I just set my timing to "total mechanical" of 36° while revving the engine and never bothered to verify the initial timing (I know... not advised). I just assumed my larger duration cam was causing the jumpy timing at idle (... again, novice mistake). It wasn't until I started to educate myself about the ignition system (mainly distributor timing) that the issue was exposed. My engine ran fine...other than the rough idle and intermittent hard starting.

Did you ever run across any explanations that recognized the PerTronix way is seemingly wrong based on your experience? The latest PerTronix instructions show the same thing and tech support guy says the same thing. Boggles the mind to think they’ve been wrong for 10 years.

I never ran into any explanation why Pertronix chose to install the advance weights and centerplate as they do. In my opinion (based on the findings within the information in this post)... Pertronix is wrong.

The only "reason" I could presume why Pertronix installs the HEI's centerplate upside down is they think the slots for the HEI advance pins (shown below) work in the same fashion as other types of distributors where the slot is the stopping/limiting point for these pins.
According to David Ray (was a designer on the GM HEI), the slots were not designed for this purpose. The slots were purposely designed to be longer so they could accommodate the many different advance curves that the HEI distributor was used for... with the weights and centerplate controlling the advance "starting and stopping" points.

 

Perfect! Much appreciated! In another week or so after I resolve a wiring problem, I'll put distributor back together with the benefit of your enlightenment. And regarding previous "novice" status, I've got you beat. One more, if I have a mild engine, and I have the GM-style weights and centerplate shown, and I have the MSD/PerTronix-style weights and centerplate shown, and I'm most interested in eventually getting to ping-free performance more than maximum performance, which set would you recommend starting with? Thanks!

 

If I have a mild engine, and I have the GM-style weights and centerplate shown, and I have the MSD/PerTronix-style weights and centerplate shown, and I'm most interested in eventually getting to ping-free performance more than maximum performance, which set would you recommend starting with?

I would start off with the GM-style weights and centerplate and see what timing numbers (initial & total mechanical) you come up with.
If the Pertronix centerplate is not adjusted, it may cause you to set the initial timing too high to get a decent "total mechanical advance" number.

 

It is good that all of you have proven what I have said, the "kit" shown is for DRAG RACING only, NOT street use. It is intended to give 17/18 crankshaft degrees, and is designed to be used with 18 to 20 degrees initial advance, and NO VACUUM ADVANCE, for DRAG RACING ONLY, not for street use.

When we did the initial large HEI development, we figured that we did not want one setup for each engine, we wanted a universal base, with changeable curves, so it would be easier to do the systems, for ALL 437 DIFFERENT EMISSIONS ENGINE CURVES. YES, THERE ARE 437 STOCK GM MECHANICAL ADVANCE CURVES.

yes, one face up, clockwise, inverted, counter-clockwise, easier to make stuff that is interchangeable, than individually confusing parts. AMC, Chevrolet, Buick, Some Cadillac, clockwise, Some Cadillac, Oldsmobile, Pontiac, counter-clockwise.

LETS GET ONE THING STRAIGHT, THERE NEVER WAS INTENTION, NOR DESIGN TO USE THE POSTS INSIDE THE MECHANICAL ADVANCE TO START, STOP, LIMIT THE CURVES. The interface of the parts does all mechanical advance functions, start, stop, limit, in curve timing, the works. THAT is why there are 437 different combinations.

Now, the ONLY, ONLY curve set that gives the right amount of street degrees, 22 crankshaft, is the ZZ series crate, and small/big block late 70's/early 80's Suburban and some truck combo, the vaunted 41 weights, 375 center, PERIOD. This will give a reasonable 12 to 14 degrees initial, added to the 22, 12 + 22 = 34, 14 + 22 = 36.

Then, to add the IDLE timing to where it likes to be, limit the vacuum advance degrees to 10 or so, to where it is golden, 22 to 24.

It is just that simple, and, it works, EVERY TIME.

The CRANE stop plate is a lot more sensible, and easier to work with than the MSD disaster.