How far is too far? Coil location

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Neal Zimmerman

Neal Zimmerman

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I am doing an electronic ignition conversion on my 68 Barracuda/340.
Because of tight quarters at the rear of the engine, plus heat, I would like to mount the coil over on either the rear of the top face of the passenger fenderwell, or maybe on firewall at furthest out point, getting close to the hinge. What do u guys think ? It would mean about a 20-24 inch coil wire. Too long? I have mounted my ECM and voltage regulator under the dash, because there's no heater box, and I wanted to keep them cool
Thanks
Neal.
 
I don't know the answer, but I do know this. The closer the better. If that helped any.
 
RustyRatRod said:
I don't know the answer, but I do know this. The closer the better. If that helped any.
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Agreed, heck, even the Main speaker cord from a Guitar head to the speakers, should be as short and fat as possible... when i was jamming in clubs and bars in the early 90s, thinkn the one fer my Marshall was 80 bucks... but Oh Man, the Tone... it's a Resistance thang
 
I have my MSD blaster 2 coil on it’s side mounted to the top of the passenger fender close to the fire wall and the coil wire is about 16 inches long. My MSD box is mounted on the inside of the passenger firewall above the footwell. Don’t have any problems. Just make sure you use the same kind of wire for the coil wire as you are for the spark plugs. Before I took the heater box out, the PO had the MSD mounted to the air box right below the glove box.
 
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I don't know what the limit is, but the primary leads might benefit from being shorter as well. The longer this all is, if you like music, it will be more difficult to control noise
 
I think the most important thing to consider with ign coil mounting is...heat. The windings are made of copper, one of the best conductors of heat. Mounting the coil on the engine is about the WORST thing you can do for maximising spark energy. Might be convenient, but it cooks the coil, wire resistance increases & coil output falls off.
High tension lead resistance due to length is of secondary [ pardon the pun ] consideration.
An in depth test done by CT magazine tested about ten HT leads of different resistances to measure HP loss. The winning leads [ highest HP ] did NOT have the lowest res leads!
 
Biggest thing I have seen with coils is not the length of the lead but if it is oil filled it has to go in the vertical positon, epoxy filled can go anyway.
 
Mine is mounted to a panel that sits on the inside of the firewall, directly behind the motor. I use the MSD coil wire. I think it's 18" long. Keeps everything tidy and away from the heat.

Edit: Worth noting that I have a very thick rubber grommet for the firewall hole that is dedicated to the coil wire. Chasing noise issues is not fun.

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Bewy said:
I think the most important thing to consider with ign coil mounting is...heat. The windings are made of copper, one of the best conductors of heat. Mounting the coil on the engine is about the WORST thing you can do for maximising spark energy. Might be convenient, but it cooks the coil, wire resistance increases & coil output falls off.
High tension lead resistance due to length is of secondary [ pardon the pun ] consideration.
An in depth test done by CT magazine tested about ten HT leads of different resistances to measure HP loss. The winning leads [ highest HP ] did NOT have the lowest res leads!
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I don't dissagree, I would never mount a coil to my engine. Mine is mounted to the inner fenderwell.

But modern cars use coil over plugs...
 
halifaxhops said:
Biggest thing I have seen with coils is not the length of the lead but if it is oil filled it has to go in the vertical positon, epoxy filled can go anyway.
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So does that mean that the factory coils were epoxy? Im pretty sure the factory mounted them horizontally as indicated in the pic at least on Small Blocks.

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mopowers said:
Nice clean install! How did you mount that plate to the firewall?
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Thank you. I appreciate that.

This car originally had AC, so the first panel uses the stock bolt holes from where the AC unit went. It also fills the firewall space where the blower motor used to be.

The second panel is attached with the use of stanchions, so it can be removed and serviced. I will eventually be switching over to the Holley Super Sniper later this Summer, so I dual drilled all of the holes for the different electronics. Makes for an easier transition.

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AAndrews said:
So does that mean that the factory coils were epoxy? Im pretty sure the factory mounted them horizontally as indicated in the pic at least on Small Blocks.

View attachment 1715938733
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I have run both BBM and SBM in sreet applications with the coil mounted on engine now for many moons, not one failure.
A race applcation is a different story.
 
I’m not sure the distance away is as important as grounding. If you move the coil off the engine, the return path for the spark will need to go through the body back to the coil. Make sure you have a ground strap from the engine to the body.
 
Mike69cuda said:
I’m not sure the distance away is as important as grounding. If you move the coil off the engine, the return path for the spark will need to go through the body back to the coil. Make sure you have a ground strap from the engine to the body.
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The coil does not have to be grounded except for the negative wire to ignition source. I have seen coils mounted on plywood and plastic.
 
Oldmanmopar said:
The coil does not have to be grounded except for the negative wire to ignition source. I have seen coils mounted on plywood and plastic.
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I had one mounted on my shop wall and it still managed to shock the hell out me!!!!
 
AAndrews said:
So does that mean that the factory coils were epoxy? Im pretty sure the factory mounted them horizontally as indicated in the pic at least on Small Blocks.
Click to expand...

No....it means they go bad cuz the oil leaks out....takes a while. :usflag:
 
An oil filled coil laying on the side can potentially have an air pocket up top with a coil winding exposed. The coil winding will eventually overheat and burn an open in the windings. With the coil vertical all the windings are covered in oil.
 
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