MSD Digital 6A Ignition Control

[cubandeathgrip]

I was thinking of getting one of these.
I had used it before a while back on an old D50 truck and it worked quite well.
A multiple spark system/ Has anyone else tried this on their Truck?


DIGITAL OPERATION
The Digital 6A and 6AL use a high speed RISC microcontroller to control the ignition's output while
constantly analyzing the various inputs such as supply voltage, trigger signals and rpm. The high
speed controller can make extremely quick compensations to the output voltage, multiple spark
series, timing and rpm limits while maintaining precise timing and accurate rev limiting. The circuits
and controller of the MSD have been thoroughly filtered to create protection against Electro Magnetic
Interference (EMI).
CAPACITIVE DISCHARGE
The Digital 6A and 6AL feature a capacitive discharge ignition design. The majority of stock ignition
systems are inductive ignitions. In an inductive ignition, the coil must store and step up the voltage
to maximum strength in between each firing. At higher rpm, since there is less time to charge the coil
to full capacity, the voltage falls short of reaching maximum energy which results in a loss of power
or top end miss.
The MSD Ignition features a capacitor which is quickly charged with 520 - 535 volts and stores it until
the ignition is triggered. With the CD design, the voltage sent to the coil positive terminal is always
at full power even at high rpm.
MULTIPLE SPARKS
The MSD produces full power multiple sparks for each firing of a plug. The number of multiple sparks
that occur decreases as rpm increases, however the spark series always lasts for 20° of crankshaft
rotation. Above 3,000 rpm there is simply not enough “time” to fire the spark plug more than once,
so there is only one powerful spark.

 

[Erik the Awful]

Just remember, that "Multiple Spark" is only at low speeds. Still, a capacitive discharge system is good stuff. The downside is that the MSD box is about 4x the size it needs to be. A large-cap HEI throws out plenty of spark, and doesn't require half a square foot of extra real estate. Personally, I'd go with the FAST box, formerly the Crane Fireball HI-6. https://www.summitracing.com/parts/fst-6000-6300 It's 2/3 the size and 2/3 the price. Plus, it doesn't need another $50 worth of crappy resistors to set the rev limiter. 10 seconds with a small screwdriver and you're set.

I do have to admit, last night I purchased the MSD/Holley Hyperspark ignition box for my truck, but only because I'm tired of farting around with the ignition system and it's plug-and-play.

 

[highwaystar]

Ran a 6A on my stock '94 5.7 C1500 for about a year, didn't notice much difference. I think it gives multiple spark up to 3300rpm? Anyway, I took it off and resold it. For a modified engine, you may see a benefit.

 

[Schurkey]

I had an old, analog 6T on my '88 K1500 for about a year. Maybe two. There's also an analog 6AL on my 'Camino; which hasn't seen 50 miles in the last ten or fifteen years.

As is so typical of MSD, the 6T box died without warning one day. Coasted into a parking lot, removed the MSD wiring, drove away on plain ol' HEI spark. Never noticed any difference in how the truck ran, started, fuel economy...nothing.

There is NO reason to add an MSD 6-series ignition except to gain a rev-limiter on any fuel-injected stock or near-stock engine.

The biggest benefit to MSD or any other spark-boxes is that they can cover-up poor carb tuning. You can't calibrate your carb to deliver a decent idle or near-idle fuel curve. Poor air-fuel ratio or poor mixture distribution causes idle and/or off-idle misfire. Engine runs terrible, stalls at idle, exhaust smells "rich"...instead of fixing the carb, you buy a spark-box. Engine runs better; leading you to think there was something wrong with the previous ignition instead of figuring out you don't know how to tune a carburetor. Car runs better, you're a hero, MSD makes big bucks.

Racing engines may be different. Notice that everyone who races with an MSD also has two of them installed, with a driver-operated switch so that when one box fails, the driver can switch to the other MSD box to finish the race. This should tell you something about MSD reliability.

Don't get me started on their Made-in-China junk ignition coils.

I fully acknowledge that the MSD multi=spark is fun to watch on an automotive oscilloscope. The spark line continues for ~20 degrees of crankshaft rotation--enormously longer spark duration that a conventional ignition. The slower the engine runs, the more sparks there are--but the overall spark duration stays about the same.

Conventional HEI; spark pattern at 1094 rpm. One firing spike per cylinder firing, short duration spark:

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MSD 6T spark pattern, 1051 rpm. Multiple spikes per cylinder firing, double or triple the spark duration:

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The firing lines look different, the MSD is very impressive...but it doesn't acutally run better if the fuel curve is right, the engine has proper compression, and the stock ignition system is in good condition.

Screw-up the fuel curve, and having a superhero ignition makes a seemingly-good band-aid.

 

[Schurkey]

Single-cylinder firing pattern, spread-out for better detail:

Conventional HEI. Single spark pulse with burn-time and coil oscillations, then dwell. The way this 'scope presents the waveform, the dwell "wraps around" to the beginning of the pattern, showng the small upward step of HEI current-limiting before the big spike at the beginning of the spark.

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MSD 6T. Four discrete spark pulses.

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I'll say it again: The MSD voltage pattern LOOKS impressive. It does not do anything USEFUL on a stock, or near-stock engine in good condition. It is a total waste of time, money, effort, and enthusiasm on a typical fuel-injected vehicle. Having a rev-limiter may be useful, but you wouldn't have to have multi-spark to achieve that.

IF (big IF) you're running to the extreme end of the RPM range, or have unusually-high cylinder pressure (supercharged, high compression ratio, nitrous, etc.) there could be some benefit if your ignition system insulation can take the potential voltage increase.

 

[Nad_Yvalhosert]

All my trucks get them. I'm sold on the potential of free-ish power. Yeah, I know I still have to buy the MSD box. But air is free, electricity is free, so there.

I had one on my wifes '99 Jimmy. Got an additional 1.5mpg. Sold the truck with it.

Had one on my '88 GMC 1500. Easier starting, no appreciable MPG increase. Came off for use in the Suburban.

Had one on my '98 Suburban 2500. No changes in running, but it didn't want to start when I removed it. I think I nearly fouled the plugs trying to start it. Threw it back on and it started immediately. Yanked it back off once the engine was warn, and refired it. Thinking the PCM advanced the timing and that was the reason it wouldn't start... Sold the truck without it.

Have one on my '00 Yukon Denali, along with a MSD coil. Seems to run smoother, start very easy.

The '95 C2500 is the next to receive the one from the '88 and the '98. And I'm planning on adding one to the parts list for the supercharged '89 I'm restoring.

 

[Erik the Awful]

GM did a very good thing back in the '70s when they invested engineering time in HEI distributors. An MSD isn't a great improvement. Other manufacturers had different results. On my RX-7, replacing the factory ignition module with an MSD was amazing, absolutely the best mod I ever did to that car. I picked up low-rpm torque, cleared up some misfiring above 7000 rpm, got a smoother idle, and better fuel economy.