MSD 6AL with HEI?
 

I have a GM stock HEI with an MSD rev limiter module (the one that replaces the stock module). This thing failed me tonight (had to tow car home) and I have also had problems in the past with GM and aftermarket HEI modules.

One of the guys I know from the dragstrip said to get a MSD 6AL and run it with the HEI with the stock coil. What are thoughts on this setup? I also read the older non-digital version is preferred vs the newer version. Is this true?

I'm not doing this for nor expecting any change in performance and pretty much going for better reliability. Is it worth the $ or should I go back to a stock GM module with a couple extras in the glove box and no rev limiter? I really like having a rev limiter especially when I make the bad decision to put the radials on the rear. The tach gets pegged QUICK!

I ran the gauntlet with aftermarket modules and ended up back with my original factory 990 module and keep a spare in the glove box.

I loved the rev limiting features they offered for sure, but offered zero performance improvement over a stock 990, and for sure they will NEVER take a dump when you are in front of Jegs or Summit Racing.......Cliff

The HEI reluctor would work fine for triggering the MSD. I haven't played with the new digital unit, but the old analog ones I use have lasted forever.

I would say that a voltage spike is taking out your modules, and probably a little more likely to be on the ground side. Many years ago I had problems with frying modules and it was actually the ground between coil and cap that was back feeding high voltage at times, but your problem could also be a bad ground with the module.

I don't know of any good racer that doesn't run MSD. HEI has fluctuation issues at high RPM. There's a reason why you see piles of HEI distributors at swap meets.

Those MSD distributors are TRASH. My son had one in his 1977 K-10, and the module fried the same as yours did with less than 5000 miles on it. This is the part that was toast:
https://www.summitracing.com/parts/msd-83647
It's a $125 Chi-Comm garbage weak link.

His died in a similar fashion to yours. It sounded a little like a miss, then would randomly die. At least the one in his Chevy did us the favor of dying for good in the garage. We pulled apart my old Pontiac HEI, threw in that old module, and "Wolverine" been running fine ever since.

If you want a great distributor that is made in the USA, call up the folks at D.U.I. Those Memphis boys will hook up you! https://performancedistributors.com/
When you get it out of the box, you will see right away how high the quality is.

If you really just want to throw money at MSD, their older analog boxes are way more reliable than the digital ones.

Being running the 6al digital box for 10 years, no issues yet. keep it cool. Mounted it behind right front headlamp to get some air flow.

You can certainly trigger an MSD box with the HEI, so you have a soft touch rev limiter. You gain multi spark discharge as well, which I kind of like myself since my cars are a pinch on the fat side at 5,000 feet, it seems to keep the plugs a little cleaner compared to the cars that I don't run a box on. If you want to use the HEI I'd try to find a stock module.

I don't really like the MSD modules in the HEI's though. I had one that was causing the car to pop and bang horribly, and it was intermittent. Other times it would run fine. MSD tested it and sent a new one no charge and I never had a problem with it since. But I tend to shy away from that deal anymore. This was probably 6-7 years ago.

I do like the MSD boxes and some of the features they offer. The neat thing is that you can trigger it with anything, I even have one car here I trigger the box with a factory points distributor and that is by far my favorite setup. I run a digital 6AL on that one.
We run a couple of the MSD billet distributors that have been flawless for 25 years, and on one of those is a digital 6 box with timing retard, 2 step etc... That box is also about the same age. The other car has a analog 6AL and it's worked fine the same amount of time.

As far as the digital boxes go, it's like any electrical item, they fail at any time and there is no set time limit. Like I said I have one digital that is more than 2 decades old that still works fine. I also have a newer digital triggered with a points distributor that isn't a year old yet, but works fine. The beauty of that deal though is that if the box ever fails, I can swap a couple wires and drive away on the points ;)

I will add however I recently installed a digital 6AL box on another car, triggered by the points distributor. Right out of the box it had a problem and wouldn't fire. I swapped a couple wires to run off the points, it fired to life and confirmed right away the box was faulty. I sent it back and it was replaced no questions asked. The new one has worked just fine.

Like I said, electrical stuff is always a crap shoot but most of the time you won't see a problem, it's not enough to worry about. As long as you have solid grounds and power supply.

Yep

For some ridiculous reason people like mounting them on the firewall or worse, the fenderwell near the exhaust manifold. Stupid. 99% of the people know heat kills electronics but those same people will mount their MSD box in or near a heat source.

I always mount mine inside the car, under the dash.

Yes, I always mount them behind the battery, behind the headlight, on the inner fender.

Not only does it keep it cool and away from most of the engine bay heat, but it also hides it. I never liked mounting that stuff out in the open for all to see. Keep that race car stuff hidden :D

This particular distributor has been rebuilt by Suntuned and has a nice advance curve, plus I finally got the mechanical advance locked in right where I want it. I really have no interest in changing it at all. I checked my stash and have 5 "990" modules from my last trip to the junkyard. I think I'll go this route for now but will keep the MSD in mind. At least if the module fails it is easy enough to change in a pinch. Easy to have an extra in the car plus the minimal tools needed to install.

I've ran a MSD 6al for years with a separate coil and an old HEI..works great.
My biggest reason really was for a rev limiter and to remove the coil from the cap..the rev limiter was a" must have" for my old engine..it saved the stock rod engine countless times.

I have two of the MSD Ready to Run distributors and programmable 6AL-2 boxes, no problems from either. One in a Pontiac 505, the other in a Chevy 396.

Not a cheap solution, but very easy and does everything I could ask for.

If you're having problems with repeat module failures, it's time to find another ignition coil.

At minimum, test the ignition coil for spark intensity using an HEI-calibrated spark tester. An ohmmeter can tell you if a coil is bad. An ohmmeter CAN NOT tell you if a coil is GOOD. But if it passes the resistance tests, isn't shorted, and will RELIABLY fire an HEI-calibrated spark tester, it should be OK.

Coils develop insulation failures. The wires which need to be insulated from each other, get "weak spots" in the insulation. High voltage can break down the insulation, which won't be shown on a low-voltage ohmmeter test. If the primary windings short, resistance goes down, spark energy goes down, amperage draw of the ignition coil increases, and the heavy current draw overheats the ignition module.

"One of the guys I know from the dragstrip said to get a MSD 6AL and run it with the HEI with the stock coil. What are thoughts on this setup?"

Makes no sense to me...does he mean use the HEI to trigger the MSD and use the stock HEI coil fired by the MSD?, or trigger the MSD with the HEI and use the stock MSD coil on the MSD?????

The only sense is to use the HEI and module to trigger the MSD/MSD coil.

George

Everything from MSD is aftermarket, there is no "stock". At best, MSD has some "stock-replacement" items.

Seems clear to me the guy meant using the "stock" HEI distributor housing, and the "stock" HEI mag-pickup (with or without the "stock" HEI module; I've done it both ways.) The MSD then fires the "stock" HEI ignition coil.

I'd add a low-resistance button under the in-cap coil; or use an external ignition coil potentially from another "stock" application such as the HEI coil used on TBI trucks. I have zero faith in the popular MSD ignition coils. The failure rate seems to be quite high, based on anecdotal evidence on the Internet.

Do you know if the HEI coil specs are suitable for being driven from the MSD Capacitive Discharge?

George

I've done it for years. Fairly sure that the MSD instructions say stock coils can be used--but Summit is having web-site problems right now. I can't confirm their instructions. Gonna have to try the MSD web site.

Although...I have failed some MSD boxes. One was outright my fault. The other two...



[EDIT:] From the Digital 6AL 6425 instruction sheet:
https://documents.holley.com/6425.pdf

[/EDIT]

I’m a little late here to the party.

As Schurkey has Sluder to above, at minimum I would replace the coil, and unless it’s pretty new might as well go ahead and put a new cap with it.

Lately, I’ve noticed if a module fails, you can almost guarantee it was one of three things that caused it.
1. A coil on its way out.
2. Welding on the car/exhaust
3.lack of heat sink compound

Even though a coil may still seem to function properly if it takes the module out, I’ve found in the last 5 years ,you can play patch the parts, or just fix the issue at hand. That I have found is a coil That ain’t far from leaving the building with Elvis. Several times we’ve replaced the module only to find out the coil will take out another one in short order.

Had a Monte Carlo up the street that wiped 4 modules in nearly 6 months. Just for the hell of it I checked out everything and decided to feed it 2 more for good measure. One day we decided to scope it,and thought hmmm.... replaced the cap and coil haven’t had an issue in a year and a half.

FWIW.

MMMMmmmmm. Automotive Oscilloscopes!

Thousands of years ago, they were a huge rolling cabinet, then they were a small rolling cabinet, and now they're hand-held. They're still the best way to diagnose ignition issues IF (big IF) you have access to the primary circuit and the secondary circuit. With coil packs, access to the coil primary is difficult, with coil-on-plug, access to the coil secondary is difficult. Sometimes there's work-arounds.

Digital storage oscilloscopes are also good for diagnosing electric motors--HVAC fan, electric fuel pump, etc. along with solenoids and relays.

Not many folks have such equipment, though.

For coil packs and coil on plug, it may be possible to use a clamp-on capacitive plate like Sun had to scope the HEI coil...ever seen one? I can take a pic of one.

George