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HEI modules absolutely need some type of cooling sink, with thermal paste, or they will burn up. There is nothing wrong with a separate HEI module, if you just neaten the wiring up. It's all a street car really needs. And it is easy to carry a spare. And spare thermal paste too!
MSD boxes also need to stay cool.. In Nascar cars they used to keep them inside to keep them cool, and they still had 2, with a quick-switch lever, reachable by the driver, to change them on the fly. They do offer the rpm limiter as a plus.
I ran a multi-spark MSD on my big cammed LT-1, and it idled significantly better after. It was mis-firing way too much before, because I was still learning about carbs back then. And with the low vacuum both the carb & ignition needed some help, but the MSD made it very driveable. It was still smelly tho LOL. Still reved to 7k with points just fine, with or without the MSD.
Your cam is milder, and it doesn't stink at idle, so I do not think the multi-spark function is going to help you all that much.
It is a very personal choice.
Thanks for the response Leigh. I think I'm going to switch it over to the MSD in the near future. If for no other reason than the rev limiter. I know there were some issues with the engine before Jeff rebuilt it, but I don't want to blow it up again. Jeff said the engine can handle up to 6500 rpm - but it's hard to watch the tach and the road at the same time.
2 other notes...
- I just spoke with Pypes - they no longer do installations. I'm going to order the 2.5" system today and maybe install in the next few weeks.
- I'd love to have you drive the car again to get your feedback. With all the new front end work the handling is much much sharper. I still need to dial in the alignment, but I need to do it in the driveway and the weather has not cooperated. Maybe I cab come out to your place...?
Oh I KNEW it would just be a matter of time before we got "thoroughly" schooled LOL
Still trying to figure out how an alternator passes a bit of alternating current due to "wear" ??
Good you got all possibilities broached and covered
Current drawn by the box (or HEI) and heat generated are proportional to the gap on the spark plugs. The electronic boxes allow a bigger spark, but that comes with more heat and larger current draw. It is important to know how much plug gap is required for your engine (to idle well, not have plug-miss, etc.) and just gap the plugs there. With time and wear, plug gap will widen a bit and cause a bit more current draw, but that should be no big deal, if the plugs are gapped properly to start.
Current drawn by the box (or HEI) and heat generated are proportional to the gap on the spark plugs. The electronic boxes allow a bigger spark, but that comes with more heat and larger current draw. It is important to know how much plug gap is required for your engine (to idle well, not have plug-miss, etc.) and just gap the plugs there. With time and wear, plug gap will widen a bit and cause a bit more current draw, but that should be no big deal, if the plugs are gapped properly to start.
That makes sense. I assume that mine were set up correctly by the engine builder. But how does one figure out what the gap should be for a custom engine? I can find some theoretical type articles online, but nothing more specific.
MSD boxes need to be wired correctly, mine is straight of the battery via the starter and a solid ground. I think most of failures are related to power and ground.
Running the power wire straight to the battery, is exactly like putting a big "filter" on it. A 32# one!
The battery "buffers" any voltage changes. So I see no need for another filter.
Audio subwoofer amps have the same need, for the same reason.
Glad to see you back Stormin Norman. Now THAT is an engine!
I like to see the remote mounted HEI modules being used. Only thing I would offer is to fabricate the mounting plate to accept 2 modules at the same time. If the one in use ever fails, you can just move the 2 wire plugs to the backup module and drive away. Replace the failed module when you have time.
I have never used an MSD brand box but my old Crane HI-6 multi spark CD box is still going strong for about the past 35 years. Plenty of good GM HEIs too. Only had 1 HEI module failure from an aftermarket junk hop up kit ONE time. Never again.
Connected straight to the battery is relatively important. The battery supplies power...but it also acts as a HUGE capacitor and filters out ALL electrical spikes, etc. That is something that is probably pretty important to the MSD electronics.
Plug gap for a relatively stock engine should be in the .035"-.040" range. The "GoFaster" vendors want to sell you on really HOT ignition systems, but only specialized engines have need of them. High compression engines require larger gaps to create enough spark energy to ignite the fuel charge properly. If your engine has a CR between 11:1 and 11.5:1, set your plugs at .045" gap and you should be fine. If that gap is too large, you will know it with mis-fires. But I doubt you will have them. If you do, lower it to .040" gap.
You can use your induction timing light on each plug wire and watch the light for the ignition pulses to look for mis-fires. And you can always pull a plug IMMEDIATELY after a run (as in, stop the car and get out the plug wrench) to get a 'visual' on plug performance.
Last edited by 7T1vette; Feb 22, 2025 at 12:53 AM.
I ran the + power from the starter and the negative from the engine ground strap next to the starter to a power block which also has my trickle charger ran to.So far so good. The MSD box is vented to the cowl so should help cool it.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by DHer67
I meant to add this video. It shows a visible comparisons of the spark generated between MSD Ignition box, "Factory" ignition, and between MSD coil and "Factory"coil on his Mustang.
Guys, I'm seeing several fables regarding ignition systems and spark plugs in this thread. But first, please don't take this guy's video serious. He knows nothing about ignition systems, and watching a spark plug sitting on a radiator support tells you nothing. A few major points about ignition systems:
1) The ignition system is designed to deliver a fixed amount of energy to the plug gap. Voltage by itself won't do squat.
2) Energy at the plug gap is gap/arc voltage X arc current X arc duration. Just like turning on a light bulb. The bulb does its job with voltage, current, and time (and gets hot!).
3) There's no free lunch in this world. Looking at the bolded formula above, if you open the gap, you increase the gap arcover voltage requirement, meaning something has to give. And that give is most always a reduction the arc duration.
4) High compression engines do not "need" bigger plug gaps. Higher compression ratios force more air and fuel molecules into the gap (which is good), but that higher compression automatically causes the arcover voltage requirement to increase, which is more (electrically) stressful to the ignition module and coil. Increasing the plug gap size just increases that stress and reduces the arc duration.
5) A casual glance at the more "upscale" ignition systems shows they all shoot for about 125-150 milliJoules of energy exiting the coil. This is big enough to light off most any engine, and low enough to keep the module from glowing red from the currents required to charge things up quickly for high RPM conditions. This energy target is calibrated/built-into the module/box. The module/box doesn't change or adjust itself to different gap sizes, as the module/box has no direct way of telling what the gap size is.
6) This energy is stored in a capacitor in CD systems (obviously), and stored in a magnetic field in inductive systems (again, obviously). Due to some plain but boring physics, a CD system and an inductive system dole out the energy in different ways. A CD system will dump the energy quickly (making a neat looking flash on any plug sitting on a radiator support, while an inductive system meters the energy out at a lower (but longer!) rate, producing an unimpressive looking spark when video'd. Imagine the ignition system energy as a five gallon bucket filled with water. Also, imagine pouring this bucket of water over your friend's head. Does he get wetter if you pour the water fast, or slow? Neither. It's the same five gallons, so he gets just as wet one way or the other.
7) Most OEM manufacturers use inductive systems because they are inherently more reliable and less costly.
8) CD systems are more easily tailored to high RPM engines as it's easier to quickly charge up the capacitor between cylinder firings compared to an inductive system.
9) In easily fouled plug conditions, often a CD system is preferred, as less potential arc energy is lost in the plug insulator carbon tracks during the short time that the gap voltage is ramping up.
10) CD multi-strike: A nice feature at idle and low RPM, but irrelevant at the RPMs where peak cylinder pressures or horsepower occurs.
My personal choice on my engine: I run an HEI module controlling the near 57 year old stock can coil. I get great system reliability, long plug life, and smooth WOT runs, all at a very modest system cost.
Guys, I'm seeing several fables regarding ignition systems and spark plugs in this thread. But first, please don't take this guy's video serious. He knows nothing about ignition systems, and watching a spark plug sitting on a radiator support tells you nothing. A few major points about ignition systems:
1) The ignition system is designed to deliver a fixed amount of energy to the plug gap. Voltage by itself won't do squat.
2) Energy at the plug gap is gap/arc voltage X arc current X arc duration. Just like turning on a light bulb. The bulb does its job with voltage, current, and time (and gets hot!).
3) There's no free lunch in this world. Looking at the bolded formula above, if you open the gap, you increase the gap arcover voltage requirement, meaning something has to give. And that give is most always a reduction the arc duration.
4) High compression engines do not "need" bigger plug gaps. Higher compression ratios force more air and fuel molecules into the gap (which is good), but that higher compression automatically causes the arcover voltage requirement to increase, which is more (electrically) stressful to the ignition module and coil. Increasing the plug gap size just increases that stress and reduces the arc duration.
5) A casual glance at the more "upscale" ignition systems shows they all shoot for about 125-150 milliJoules of energy exiting the coil. This is big enough to light off most any engine, and low enough to keep the module from glowing red from the currents required to charge things up quickly for high RPM conditions. This energy target is calibrated/built-into the module/box. The module/box doesn't change or adjust itself to different gap sizes, as the module/box has no direct way of telling what the gap size is.
6) This energy is stored in a capacitor in CD systems (obviously), and stored in a magnetic field in inductive systems (again, obviously). Due to some plain but boring physics, a CD system and an inductive system dole out the energy in different ways. A CD system will dump the energy quickly (making a neat looking flash on any plug sitting on a radiator support, while an inductive system meters the energy out at a lower (but longer!) rate, producing an unimpressive looking spark when video'd. Imagine the ignition system energy as a five gallon bucket filled with water. Also, imagine pouring this bucket of water over your friend's head. Does he get wetter if you pour the water fast, or slow? Neither. It's the same five gallons, so he gets just as wet one way or the other.
7) Most OEM manufacturers use inductive systems because they are inherently more reliable and less costly.
8) CD systems are more easily tailored to high RPM engines as it's easier to quickly charge up the capacitor between cylinder firings compared to an inductive system.
9) In easily fouled plug conditions, often a CD system is preferred, as less potential arc energy is lost in the plug insulator carbon tracks during the short time that the gap voltage is ramping up.
10) CD multi-strike: A nice feature at idle and low RPM, but irrelevant at the RPMs where peak cylinder pressures or horsepower occurs.
My personal choice on my engine: I run an HEI module controlling the near 57 year old stock can coil. I get great system reliability, long plug life, and smooth WOT runs, all at a very modest system cost.
Speaking for myself. as with my other vettes, after an MSD install this 1980 fires up instantly. Before it would have to crank a minute to start. It definitely has better throttle response . I'm going to buy a spare. Take a couple minutes to plug a new one in to get home in a failure event.
