Coil wire length
Thread Starter
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Coil wire length
Does the coil wire length really matter. I have always tried to keep it as short as posible but what if it was 2 or 3 feet long. Is it going to hamper voltage or performance?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
look at all cup & arca cars past few years ... rules require all have coils & cds atop dash ... so 2-3 feet between coil & cap ain't an issue.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
For 'regular' wire coming off a 12v. supply, length is NOT an issue. If the coil requires a given length of resistance wire [in order to establish a lower coil voltage when in running mode], then wire length IS an issue.
Thread Starter
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I'm looking at about a 2 foot distance from the coil to the dist. So it does not look like that will be an issue. The coil I have is pretty big and there is just not much room to mount it close to the distributor.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Gordon:
I'm fairly certain you're talking about the 7-9mm dia hi-tension "plug" wire from coil to center of MSD dist cap ... don't sweat 2-3 ft ... think of the race Fords with dist in front & coils on dash ... LONG run. Pretty dang unlikely you're running a resistance wire with a cd box as there's no 12vdc wire to either coil primary. Box supplies coil and box requires full 12vdc at all times.
a tip on wiring cd box-dist ... that pair of small primary wires that run from the cd box to the distributor ... at minimum, TWIST that pair about 1-2 twist per inch ... or shield them within a conductive jacket ... or both. Those are the trigger wires & twist/shield is how you help prevent interference from accidentally triggering a plug in the wrong phase.
I'm fairly certain you're talking about the 7-9mm dia hi-tension "plug" wire from coil to center of MSD dist cap ... don't sweat 2-3 ft ... think of the race Fords with dist in front & coils on dash ... LONG run. Pretty dang unlikely you're running a resistance wire with a cd box as there's no 12vdc wire to either coil primary. Box supplies coil and box requires full 12vdc at all times.
a tip on wiring cd box-dist ... that pair of small primary wires that run from the cd box to the distributor ... at minimum, TWIST that pair about 1-2 twist per inch ... or shield them within a conductive jacket ... or both. Those are the trigger wires & twist/shield is how you help prevent interference from accidentally triggering a plug in the wrong phase.
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Thread Starter
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Gordon:
I'm fairly certain you're talking about the 7-9mm dia hi-tension "plug" wire from coil to center of MSD dist cap ... don't sweat 2-3 ft ... think of the race Fords with dist in front & coils on dash ... LONG run. Pretty dang unlikely you're running a resistance wire with a cd box as there's no 12vdc wire to either coil primary. Box supplies coil and box requires full 12vdc at all times.
a tip on wiring cd box-dist ... that pair of small primary wires that run from the cd box to the distributor ... at minimum, TWIST that pair about 1-2 twist per inch ... or shield them within a conductive jacket ... or both. Those are the trigger wires & twist/shield is how you help prevent interference from accidentally triggering a plug in the wrong phase.
I'm fairly certain you're talking about the 7-9mm dia hi-tension "plug" wire from coil to center of MSD dist cap ... don't sweat 2-3 ft ... think of the race Fords with dist in front & coils on dash ... LONG run. Pretty dang unlikely you're running a resistance wire with a cd box as there's no 12vdc wire to either coil primary. Box supplies coil and box requires full 12vdc at all times.
a tip on wiring cd box-dist ... that pair of small primary wires that run from the cd box to the distributor ... at minimum, TWIST that pair about 1-2 twist per inch ... or shield them within a conductive jacket ... or both. Those are the trigger wires & twist/shield is how you help prevent interference from accidentally triggering a plug in the wrong phase.
I was running a Carne HI6 and a MSD magnetic dist. I did have those wires twisted and that setup ran flawless for many years. The rev limiter was set at 7000 rpm and I used it often.
Most all of it will be for sale once I get the FI up and running. Thanks for the info.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Some of the historic race cars have 3 foot long coil wires with the ignition/rev limiter boxes on the passenger side dash to keep it all away from engine heat
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Drops less voltage if its still shorter than your plug wires.
It depends on the resistance of your wire. Some spiral core wire has over 50ohms per foot reistance. The longer the wire the greater the voltage drop and the less your sparkplug sees. Now most race wire has very low resistnace (1 or 2 ohms) and would not be sigificant. Well really 2 or 3 feet will be very hard to notice if your running aftermarket ign box that boosts the voltage a bunch (MSD etc.).
Okay so lets do the math so you can sleep tonight Gordon. With a 10,000 volt coil output and only 1 foot coil wire at 50ohms/ft then current is 10,000 divide by 50 = 200amps (instantanious) to the spark plug. Now with 3 feet of wire then 10,000 divide by (50 times 3) = 66.7 amps - a major change in spark energy.
And for a hi-energy ign at 50,000 volts: then 50,000/50 @ 1ft = 1000 amps and 50,000/(3'x50) = 333.3 amps.
But this is only chalk board talk as in reality the plug don't fire until enough electrons stack up at the gap - like a buildup before the dam breaks. I think this is why most ignitions rate thier outputs in joules of energy which is work done(at the spark gap).
Not to scare you here and so can sleep tonight just remember the spark has to continue to travel through the dizzy (jumping the rotor gap also) and down even more plug wire resistance to the spark plug. So if the coil wire is still shorter than the plug wire you haven't done anymore damage to the spark energy than the plug wire will do.
Good night,
cardo0
Okay so lets do the math so you can sleep tonight Gordon. With a 10,000 volt coil output and only 1 foot coil wire at 50ohms/ft then current is 10,000 divide by 50 = 200amps (instantanious) to the spark plug. Now with 3 feet of wire then 10,000 divide by (50 times 3) = 66.7 amps - a major change in spark energy.
And for a hi-energy ign at 50,000 volts: then 50,000/50 @ 1ft = 1000 amps and 50,000/(3'x50) = 333.3 amps.
But this is only chalk board talk as in reality the plug don't fire until enough electrons stack up at the gap - like a buildup before the dam breaks. I think this is why most ignitions rate thier outputs in joules of energy which is work done(at the spark gap).
Not to scare you here and so can sleep tonight just remember the spark has to continue to travel through the dizzy (jumping the rotor gap also) and down even more plug wire resistance to the spark plug. So if the coil wire is still shorter than the plug wire you haven't done anymore damage to the spark energy than the plug wire will do.
Good night,
cardo0
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
No PM please, initial email thru this forum AOK. Is it TPI injection? Is coil same/similar to OE TPI coil?
