[Nick_R_23]

The reason you wouldn’t want a larger gap is because it becomes less reliable over RPM, compression, and wear as components are used. Here’s a crude comparison: Think of you running along a road filled with potholes, large enough that you have to jump over them. You’re the spark, and you need to bridge that gap. Smaller potholes are easy to jump and don’t require much energy, while still getting you across. Larger potholes are harder to jump, and while still getting you across, it takes more effort (energy), wearing you down and tiring you out. The more of these you have to jump, the higher of a chance there is that you (the spark) might not complete the jump. Now, imagine the same scenario, except you have a massive windstorm pushing back against you - this would be like increasing compression. You can still jump the same smaller potholes, or you may want to stick with even smaller ones (gaps) than you were before, just to guarantee you (spark) make it across. The larger ones you may not even make at all, due to the wind pushing back too hard, especially if it was already a difficult jump before.

You may not notice ignition effects much in a stock engine with low compression ratios. They’re designed to operate on pretty much everything being out of whack and still remain in service. Perfect example: My 400’s ignition timing being 14* ATDC, burnt plug wires, deposits on plugs, and still being used as a daily driver. Correct? Definitely not. Functional? Absolutely.

On a side note, I’m not really a big believer in MSD boxes. Don’t get me wrong, they do work! But their effects are completely diminished by 3000 RPM, which by then, you’d definitely want the benefits of a good quality ignition system in place anyway, sort of rendering the box useless. If you can produce great spark at high RPM under high cylinder pressure, you won’t have a problem at low RPM. The point of an MSD box is to take advantage of the longer dwell time at low rpm, and fire the coil repeatedly in that period, creating the “Multiple Spark Discharge” nameplate. The original idea behind this, is that at low RPM, your spark is weak and multiple sparks occurring during a normal “1-spark” period, will mask the effects of a weak spark possibly causing an incomplete combustion. However, this effect ends at 3000 RPM, which is an operating range seen mostly by stock vehicles, or daily driver used performance vehicles. In those cases, will you see a difference? Very likely, but less so if your ignition system is in great shape to begin with. Reference back to the ‘Preventing a loss rather than creating a gain’.

My personal feelings are that I would rather just start out with a well built high energy system, because if you’re consistently turning over 3000 RPM, you’ll find the most benefit at higher RPM (which is where true race engines spend their time), which also automatically translates to better spark at all RPM, including lower RPM. The longer dwell time at lower RPM also equals better coil saturation, which equals more energy for a better spark, so by having a better system to start with, you automatically create a better low RPM spark and negate the need for multiple sparks in that low RPM window. Not that it would really hurt anything to run an MSD box (although they do offer other means of control such as RPM limiting, timing retards, etc that are very beneficial!), you just may not get much, if any, improvement in that regard. Keep in mind that MSD was developed in the 70’s when points were commonplace and ignition system capabilities were extremely limited compared to what they are today.

I do have pretty extensive background on motorsports in general, although I’m far from knowing everything there is to know about engine theory. I certainly wish I could be there! :P I do a lot of research and seek out the info posted on forums from a lot of the ex-engineers from GM, Ford, Chrysler, which is usually incredibly long reads but amazing information, one of the best resources you’ll find out there in my opinion. I have a hand in building many of the circle track championship-holding engines here locally, although I’ve slowly moved out of that scene recently, it’s a fun way to see how real world changes apply when it comes to tuning.