MSD box - do you really gain anything?
 

I see MSD boxes on a lot of hot rods and muscle cars.

Is there any real gain over say a basic MSD Pro Billet distributor without the 6A box?

I suspect you get virtually nothing.

Has anyone actually done dyno pulls to prove what you gained?

John

John,

I am not sure if the box adds to HP, but I imagine that someone will provide that information. What I can say that the box gives you that a distributor alone does not provide is a rev limiter. In most street situations, you probably do not really need a rev limiter, unless you screw up shifting, miss a gear and punch it. If however, you ae going to track a car, then a rev limiter is a must because you do not always have your eyes glued to the speedometer or tach and it s easy to over rev an engine.

My two cents. Looking forward to what others have to say. Why is it that you ask?

Jim

copied this from MSD site

Inside the Digital 6AL you'll find a microprocessor that monitors and controls every firing and rev limit. The circuits are updated with efficient components that help the ignition produce more power while drawing less current! In fact, the Digital 6AL delivers over 530 volts to the coil with up to 135mJ of spark energy for every firing! Increased output combined with MSD's proven
multiple spark series is a win-win situation!


hotter spark, multiple spark per cycle and I think that is below 3,000 prms.
Rev limiter

Depends on the engine. The ignition system will only produce as much energy as it needs to make a spark. If it only needs, say, 50 joules, then that's all it will make.

On a high compression or FI engine, it can be difficult to produce a spark, so the added energy will make more power in that engine.

Multiple spark only works up to about 2,500 - 3,000 rpm. After that, it's too fast to make things happen in a single coil system. It gradually tapers back down to 1 spark per event. Most street engines spend the majority of their time below 3K. Multiple sparks can increase fuel economy and and decrease emissions.

The basic Pro-Billet MSD distributor won't work without a box. The "Ready to Run" distributor doesn't require one, just a coil.

The R2R distributor has a built in rev limiter.

Brent - you start work early.

Thanks for the reply.

Is is safe to say, for my application the MSD box is just eye candy?

I knew the R2R had a rev limiter, which is important.

John

I personally don’t like having everything in the distributor, that’s like having an integrated video card on a motherboard in a PC. If it goes bad, you’re replacing the whole nine.

I can't speak to dyno numbers but I can say that on my flat-6 911 with Webers the MSD box made a substantial improvement in cold-start, idle, and low-mid range rpm manners. It also pulled more smoothly and harder to a 7300rpm redline.

My Cobra had one when I bought it so I can't compare before/after, but it also starts immediately on the first turn of key even after sitting and also pulls hard to 7K rpm.

I have the same results with my 289 Slabside.

John
ERA #3010 Slabside 289 SB BRG

Is there an equivalent from someone besides MSD? More reliable? I personally went through two of the boxes (in fact, I made a wiring harness to make it easier to swap).

My CD box (MSD manufactured, Summit branded) is under the dash on the cool side of the firewall. That box replaced an analog MSD 6AL that was on the firewall and failed. Was that failure heat-related? I don't know, but electronics and heat often don't get along too well.

I also replaced the oil-filled coil with an epoxy-filled one at the same time, and mounted it on the firewall.

A Crane box is very robust and we have used the Pertronix products with good results. It seems that the MSD quality is suspect as most of the products are Chinese save for the pro racing ($$$$) units. A common failure on the 6AL is the small internal fuse that requires soldering to replace.

You need voltage to make a spark jump across air. The higher the voltage the more powerful the spark, and the longer distance it can jump. You start adding things to the air, like fuel, you need more current to push the spark across the gap. All the theory I lack, but here are some takeaways.

Cold weather cold start needs a hotter spark to light the poorly vaporized fuel.

A weak spark can cause a lean engine to backfire. Richen the fuel or a hotter spark will stop the backfire. The hotter spark is usually the better solution.

Boosted engines need a hotter spark.

If you have a decent ignition system that is hot enough to make the engine run well, adding a MSD gains no power. If you do gain power, it was because your ignition system wasn't good enough.

MSD has often been proven to retard timing at high rpm. One chap measured 20^ timing loss at 10,000 rpm, but didn't state at what rpm this starts to occur. I expect it is above 7000 rpm. It's suspected that it has to do with the time require to charge or discharge the capacitors.

I do believe MSD has enough power to stop your heart if get into it and get a good ground where the current flows across your heart.

As for the multi spark at lower rpms, it may do something, but it seems to me that a good hot spark that lights the fuel shouldn't need a second spark. If the 2nd spark does in fact light the fuel in a different spot, you now have two flame fronts heading toward each other. At high load, I could see this collision causing detonation. Just thinking out load.

Personally I have 1990 factory EFI that is controlling the spark with a distributor. I have never experienced anything that makes me believe I need anything hotter. I am a believer in the don't fix it, if it isn't broke camp. Never add complexity to solve a nonexistent problem, unless there is a real tangible benefit. I cannot tell you the number of threads on this site that fall under "help troubleshoot my broken MSD," but it is a big number. I do not recall a single thread of I just put a MSD in and it performed something wonderful.

That said the 60's point system are not up to snuff, but I expect there are things that are good enough, other than MSD.

Fuse? How about the lack of reverse polarity protection? If my $30 battery charger has it you'd think it should be standard equipment in an ignition box.

I have no doubt there could be timing issues with an ignition box. I'm not running 10,000 RPM, or even 7,000, but I do know there were huge differences in timing when I replaced an analog MSD 6AL with the digital equivalent.

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Old dog. - are you running a rev limiter?

Did not have one in mine and Mike Forte told me when he built the engine, “it’s just another thing to fail.” I am sure they are good for some but for me never needed it and heard a lot of stories with them failing.

I have an EEC IV A6L. I have a quarter hoarse chip that I never did get around to finishing my changes and tuning it. It is my understanding that the factory tune is set to rev limit at 7000. I have hit it a couple of times by mistake, and I was around 7000 rpm. I have no doubt it works, but I got out of the throttle instantly, so I do not know for certain how well it holds the rpm at the limit.

I intend to test it by temporarily setting it down around 3000 rpm, but I have not done that yet. Turning the spark and/or injectors off and on to control rpm seems like something I don't want to do to my engine at WOT and 7000 rpm.

So in short I think all Ford factory MP EFI systems have a rev limit in them since at least 1989. Possibly earlier throttle body did as well, but I know nothing about them.