3 ohm vs 1.5 ohm ignition coil

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Abodysrule

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OK, so on my slant six I was running a 3 ohm Pertronix coil, no ballast resistor, with factory mopar electronic ignition. I'm swapping to a v8, and I read on the Pertronix website that the 3 ohm coil is for 4 and 6 cylinder applications, but for a v8 one should use the 1.5 ohm coil? Am I not OK with my 3 ohm coil, should I switch to a 1.5 ohm coil? If so, why is that true?

Brian
 
Factory Service Manual does not list different coils for Slant 6 versus V8. The 1.5 ohm coil and a 0.6 Ballast Resistor is the best match to the Factory Electronic Ignition set up.
 
I read (for what that's worth) that you are looking for a total resistance in the primary circuit between low 2's and 3. This includes coil and ballast resistance added together.........Don't know if it's true.
 
CFD244 said:
I read (for what that's worth) that you are looking for a total resistance in the primary circuit between low 2's and 3. This includes coil and ballast resistance added together.........Don't know if it's true.
Click to expand...
OK, so let's just go with that logic...it suggests that I'm OK with the 3 ohm resistor coil with the v8. It could be that Pertronix's guidance applies to their particular other peripherals, at least it seems to read that way.

Where did you read this? Please share...
 
Abodysrule said:
OK, so let's just go with that logic...it suggests that I'm OK with the 3 ohm resistor coil with the v8. It could be that Pertronix's guidance applies to their particular other peripherals, at least it seems to read that way.

Where did you read this? Please share...
Click to expand...
I don't recall where I read it.....Unfortunately. I think it was another car forum. I was trying to figure out how to match one of my coils to the 1.5 ohm resister that I happened to have....I ended up using the coil that totalled between 2.3 and 3 ohms. This is on my run stand.
 
Any ign system that uses a coil with a 3 ohm primary resistance is going to have low-ered spark energy. The GM HEI system replaced a points & bal res system in GM cars that had very similar characteristics to the Mopar points system. The HEI with it's 0.6 ohm coil produces 85% more spark energy than the points it replaced.

So I would look for a better ign system &.............Pertronix would NOT be high on my list...
 
Bewy said:
Any ign system that uses a coil with a 3 ohm primary resistance is going to have low-ered spark energy. The GM HEI system replaced a points & bal res system in GM cars that had very similar characteristics to the Mopar points system. The HEI with it's 0.6 ohm coil produces 85% more spark energy than the points it replaced.

So I would look for a better ign system &.............Pertronix would NOT be high on my list...
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Yes, thank you, I'm aware that the GM HEI system is superior, I've seen the testing and so forth on slant six forum, great stuff. So, do you know why 3 ohms would be specified for 4 and 6 cylinders and lower resistance for v8's? That's the part I don't get. Why would one not want more spark energy on any engine configuration?
 
I am not an electronic guy, I have an FBO module, 1.5 ohm Petronics coil and bypassed ballast resister, Mopar dist. Just because this was specified. Must depend on the system used and not crossing over mismatched mfr's parts.
 
Do not know 4/6 cyl would have such high resistance; but here is something to think about.....

The power [ watts ] developed in the primary resistance is transferred to the secondary winding to produce spark energy. The formula for power is voltage squared divided by resistance. So when resistance gets bigger, the power output goes down.
 
Demon 408 said:
Factory Service Manual does not list different coils for Slant 6 versus V8. The 1.5 ohm coil and a 0.6 Ballast Resistor is the best match to the Factory Electronic Ignition set up.
Click to expand...

CFD244 said:
I don't recall where I read it.....Unfortunately. I think it was another car forum. I was trying to figure out how to match one of my coils to the 1.5 ohm resister that I happened to have....I ended up using the coil that totalled between 2.3 and 3 ohms. This is on my run stand.
Click to expand...
Here is a printout of an electronic kit from Rick Ehrenberg:

RE 1AA.JPG


RE 7A.JPG
 
OK, so I think that is suggesting that certain ECU's must have at least 1.4 ohms of resistance in the ignition coil or they'll burn out. I've read a number of articles since I posted, and I believe I'm OK with the 3 ohm coil, it just may put out a less hot spark. One post on Slantsix boards explained that since 8 cylinders are firing faster than 4 or 6, one may want less resistance so the coil can respond more quickly, something to that effect.

See here: Ballast Resistor Selection - Slant Six Forum
 
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I spoke with Pertronix, they indeed recommend a 1.5 ohm coil for V8 applications...though I could not get them to opine specifically on the mopar orange box in that regard. I do recall someone on the slant six boards telling me years ago that if I'm removing my ballast resistor (which I did) then I should go with the 3 ohm coil if I'm using the orange box, but that advice may have been specific to the slant six, not sure.
 
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