MSD box - do you really gain anything?

[olddog]

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.

[cycleguy55]

Originally Posted by olddog

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.

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.

[BigGuy]

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Old dog. - are you running a rev limiter?

[olddog]

Originally Posted by BigGuy

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Old dog. - are you running a rev limiter?

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.