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Greater spark plug gap with HEI distributor? Why? |
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Thor 
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Joined: Apr/17/2011 Location: MONTANA Status: Offline Points: 8 |
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 Topic: Greater spark plug gap with HEI distributor? Why?Posted: Apr/22/2011 at 9:37pm |
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I have read, in several places, that if one is using an HEI distributor it's good to increase the gap from the usual .035 (on a 360ci engine) to .050. I did it, and it runs fine, but it ran fine at .035 too. What have I gained by increasing the gap to .050?
Edited by Thor - Apr/22/2011 at 9:59pm |
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poormansMACHINE
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Charter Member Joined: Jun/28/2007 Location: Shoemaker-Levy9 Status: Offline Points: 12302 |
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Posted: Apr/22/2011 at 9:43pm |
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Nothing really.
The potential to fire a leaner mixture the potential to fire with a higher compression engine You will burn up caps and rotors quicker If t didn't need it, you really didn't gain anything. |
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Thor
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Posted: Apr/22/2011 at 9:53pm |
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Well crap! Guess I'll be pulling the plugs and re-gapping them then...don't want to burn the cap and rotor. Thanks for your advice. By the way, what do you recommend for the gap?
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Jeep360
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Joined: Dec/06/2010 Location: Tennessee Status: Offline Points: 87 |
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Posted: Apr/22/2011 at 10:08pm |
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you will love the HEI. I put a 65,000 volt coil in mine and it runs better than the very very crappy Ford system that AMC used. Buy the "make your own wire" sets from MSD, Accel, ect... cause getting a direct fit one from manufactures is somewhat hard to find plus the wires usually end up being way to long.
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Jeeps aren't bought they're built.
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poormansMACHINE
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Posted: Apr/22/2011 at 10:12pm |
It's not going to burn out in a week or month so no disaster. You're probably not putting that many miles on it. It's just the higher the gap, the higher the voltage has to charge to jump across. I've always run .040"~.045". Others may have different numbers to share. |
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Traveller
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Posted: Apr/22/2011 at 10:14pm |
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The cap and rotor should be fine since the system was designed for a wider gap. If you get the Davis Unified Ignition for AMC which is basically a souped up HEI, they recommend .055-.060. If you have a coil that can fire a strong spark through the gap (they can), then it will contribute to a better, more consistent ignition of whatever is in the chamber.
The neat thing about running the stronger spark and wider gaps is that even if you aren't running the best fuel/air mix it will fire it. Forget about flooding it as you probably won't unless you're dumping a lot of raw fuel in. The distributor cap and rotor won't wear any faster than they do on a system designed for a small gap. The caps and rotors last 60K easily in stock applications and usually longer. The have a tendency to fail modules from time to time, but a lot of that can be blamed on import aftermarket replacements. The OEM modules go over 100K no problem and usually longer. The HEI design is far superior to what Ford, Chrysler and AMC were using at the time. That's one of the reasons that it has continued to be used in the aftermarket as it's a good, simple, self contained system that really helps performance. I don't mean just output, but rather all levels of performance. Cold start, throttle response, etc. Just make sure that the advance curve is what your engine wants. I've used Davis Unified on Fords, Chryslers, GM and soon my AMC. Can't beat it for the price. |
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billd
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Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Posted: Apr/22/2011 at 10:16pm |
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Just remember - just because it has a 65,000 volt coil does NOT mean that's what it's putting out. It's only going to put out what is required to fire the plugs. If it takes 40,000, that's all your coil will put out. The big number looks cool, sounds good, but is meaningless on most engines. You need to be running some higher compression and/or lean mixtures to need that kind of voltage.
Better than points, yes, but not really necessary on a properly tuned and in good physical condition engine that's mostly stock and not pushed hard.
If it didn't run well on the stock motorcraft system, then it's possible that:
A. you have a higher compression engine, perhaps radical cam
or
B. you're engine is in less than ideal condition,
or
C. The fuel system needs some work.
The Ford system, especially if tweaked a bit, is more than adequate........ check online to see how they've been modified to preform just as well as anything else.
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jeremy0711
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Posted: Apr/22/2011 at 10:43pm |
Getting hard to find now but the four banger cars have a shorter harness in the 70-80 models. 
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nda racer
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Posted: Apr/22/2011 at 11:14pm |
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Back in 1975 when GM started using HEI, they wanted plug gaps set at .060 till they found out it was hard on caps and rotors, as mentioned. They then changed their specs to .045. So as mentioned, .040-.045 is right on the money.
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billd
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Posted: Apr/23/2011 at 6:41am |
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Try .080
That was their first spec (I went to GM schools back then and have the training materials)
They went to .060 - that was still an issue, so they dropped to .045.
We changed so many dozens of rotors we had trouble keeping them in stock.
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Thor wrote: