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******* SPACESTATION
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Discussion Starter · #1 ·
Just a little information on what the difference, in resistance, is between stock 7mm, Accel 7mm, and MSD 8.5mm wires is.

Stock 7mm: 11.94 k ohms
Accel 7mm: 10.99 k ohms
MSD 8.5mm: 100.1 ohms
These were all 27" coil wires.
The plug wires vary in resistance related to length.


Just some information for those of you debating about going with larger wires or not when doing a tune up.

I ended up getting the MSD 8.5mm red since I have the MSD Blaster 2 coil.
But, even with a stock coil, the resistance being lower can only help.
 

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Yea boooyeee!
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With a stock coil, you can end up burning out the coil if you have improper resistance. Or so I was told by tech support when I burned up 3 Napa coils on my '92 Dakota. I replaced the coil and the wire set, with normal 7MM stock wires, never had the problem again.
 

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******* SPACESTATION
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Discussion Starter · #3 ·
With a stock coil, you can end up burning out the coil if you have improper resistance. Or so I was told by tech support when I burned up 3 Napa coils on my '92 Dakota. I replaced the coil and the wire set, with normal 7MM stock wires, never had the problem again.
Didn't know that, good information though.
 

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Mmmmmmmmm, beer.
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Ya, stock coil requires higher resistence wires, that's part of why they go with the 7mm. The aftermarket coils like MSD are designed to operate with lower resistance wires. Question I have always had is if you will need to replace plugs more often with an MSD type ignition and lower resistance wires (not from fouling, but from overheating or faster deterioration of the center electrode).
 

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Discussion Starter · #5 ·
Ya, stock coil requires higher resistence wires, that's part of why they go with the 7mm. The aftermarket coils like MSD are designed to operate with lower resistance wires. Question I have always had is if you will need to replace plugs more often with an MSD type ignition and lower resistance wires (not from fouling, but from overheating or faster deterioration of the center electrode).
I wouldn't think so, they are not firing longer, or more often. I don't think it's the voltage that wears the plug out as much as the number of times it fires.
Most plugs last atleast 30,000 miles, so even if it decreases plug life by a lot (20%), you would still get 24000 miles out of a set. Given that the increased energy (spark) should promote better combustion (better mpg) it would be worth it.
 

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Derelict
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chizzle1 said:
But, even with a stock coil, the resistance being lower can only help.
Not really since the wire is connected to a spark gap with a resistance of zillions of ohms. Once the plug lights up (and the gap resistance drops to zero) the resistance slows the coil discharge and lengthens the spark duration (most plugs have an internal resistor). So the coil, wires, plugs have to be matched for everything to work properly.
 

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Discussion Starter · #7 ·
Not really since the wire is connected to a spark gap with a resistance of zillions of ohms. Once the plug lights up (and the gap resistance drops to zero) the resistance slows the coil discharge and lengthens the spark duration (most plugs have an internal resistor). So the coil, wires, plugs have to be matched for everything to work properly.
While I'm not completely disagreeing with you...I don't totally subscribe to this theory.
The coil discharging being slowed, if at all, would only be a fractional amount. When a ignition coil fires, it has a 'field' that rises and collapses every time. I don't think it's the resistance of the wires that slows the coil discharge, as much as it might slow the collapse of said field.
Regardless, I do see what you are getting at, but again it would only be a fractional amount.
Even if the above was true, wouldn't more energy delivered to the spark plug producing a 'hotter' spark be more efficient than a 'cooler' longer duration spark? Once the air/fuel is ignited the plug's job is done.


edit: by the way: got the MSD wires on and re-terminated the coil wire for proper fit. So far so good. Not getting the induction / crossfiring problems I was having with the 7mm. I will check upon next fill up if anything improved or worsened in the MPG dept and update. i don't see the wire making more than maybe .5 mpg difference, if any at all.
 
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