Plug Wire Ohmage Question
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Joined: Jul 2003
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2006 SL65 ///AMG - GONE BUT NOT FORGOTTEN: 2005 E55; 2002 ML55; 2001 CLK55; 1992 BMW 850i; 1991 M5
Plug Wire Ohmage Question
Just picked up the beast last night. WELL worth the wait. She is now a true Kleemann Stage 2 car with the addition of an EVO cooling kit, PTE thermostat, VRP CF airbox, EVO center resonator delete, EVO plug wires and Iridium no. 7 plugs. UNGAWDLY power. The K-2 flash, headers and primary cat delet REALLY woke that motor up - and I thought it was fast before!
Here's my question: my tech informed me that the factory plug wires incorporate 2 ohm resistors. EVOs use a 5 ohm resistor. Bigger value resistor apparently means less resistance, hence the 'performance' value of these wires over stock. Has ANYBODY ever heard of any ignition problems running a higher resistance value plug wire with the ignition syspem on these kompressed cars???
Long ago, I had service on my old GMC Jimmy and the tech put in LOWER resistance spark plugs by accident such that the coil and distributor were putting out more juice than the lower value plugs could safely handle. They shorted out and ultimately fried the distributor. This example appears to be the opposite direction I went with the 55 - the EVO plug wires provide less resistance, not more - but I just wanted to make sure I am not borrowing trouble down the road.
Again, for what it's worth, the car is an absolute brute.
Here's my question: my tech informed me that the factory plug wires incorporate 2 ohm resistors. EVOs use a 5 ohm resistor. Bigger value resistor apparently means less resistance, hence the 'performance' value of these wires over stock. Has ANYBODY ever heard of any ignition problems running a higher resistance value plug wire with the ignition syspem on these kompressed cars???
Long ago, I had service on my old GMC Jimmy and the tech put in LOWER resistance spark plugs by accident such that the coil and distributor were putting out more juice than the lower value plugs could safely handle. They shorted out and ultimately fried the distributor. This example appears to be the opposite direction I went with the 55 - the EVO plug wires provide less resistance, not more - but I just wanted to make sure I am not borrowing trouble down the road.
Again, for what it's worth, the car is an absolute brute.
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From: Caribbean/Florida/Colorado
E-ZGO 53hp., 1999 E 430 sport, 2004 E 55, 2008 Tahoe LTZ on 24"s
Lower number Lower resistance.
The OEM will deliver a hotter more precise spark because they have a lower resistance.
The OEM will deliver a hotter more precise spark because they have a lower resistance.
Last edited by Yacht Master; May 13, 2009 at 08:12 PM.
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Joined: Oct 2007
Posts: 161
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From: Corona, CA
2004 E55 AMG; 1995 Porsche 993 Cab.
Oh dear... some basic properties of electrical circuits. ( BTW. lower Ohm value == lower resistance)
V = I x R
V= Volts
I= Current (in amps)
R= Resistance (in Ohms)
So assuming the coil gives out a fixed voltage (a few tens of thousands of volts to get a spark in a plug - free air breakdown is about 3Kv per cm before you get a spark - inside a compressed cylinder with fuel and a tight gap it's a lot more!), then *increasing* the resistance will give a lower current path for a given fixed voltage - once the spark starts the plug resistance is negligible, it's all in the wire.
As Power (Watts) is given as W = V x I, then if the current is smaller, and the voltage fixed, the given power is less. (as you've lost some power to the inline resistance of the wire).
I would imagine MB uses 2 ohm leads to reduce the chance of shorting out the ignition coils, and adds some "protection" Adding some impedance also reduces the RF (radio frequency) energy (noise) when the spark fires. Increasing the resistance only adds more "protection", but will also reduce the power into the plug (lower "energy" spark).
Doesn't sound right to put 5 Ohm leads in, as this will reduce the spark "energy".
V = I x R
V= Volts
I= Current (in amps)
R= Resistance (in Ohms)
So assuming the coil gives out a fixed voltage (a few tens of thousands of volts to get a spark in a plug - free air breakdown is about 3Kv per cm before you get a spark - inside a compressed cylinder with fuel and a tight gap it's a lot more!), then *increasing* the resistance will give a lower current path for a given fixed voltage - once the spark starts the plug resistance is negligible, it's all in the wire.
As Power (Watts) is given as W = V x I, then if the current is smaller, and the voltage fixed, the given power is less. (as you've lost some power to the inline resistance of the wire).
I would imagine MB uses 2 ohm leads to reduce the chance of shorting out the ignition coils, and adds some "protection" Adding some impedance also reduces the RF (radio frequency) energy (noise) when the spark fires. Increasing the resistance only adds more "protection", but will also reduce the power into the plug (lower "energy" spark).
Doesn't sound right to put 5 Ohm leads in, as this will reduce the spark "energy".
Last edited by D Bst; May 12, 2009 at 09:53 PM.
Thread Starter
Senior Member
Joined: Jul 2003
Posts: 460
Likes: 14
2006 SL65 ///AMG - GONE BUT NOT FORGOTTEN: 2005 E55; 2002 ML55; 2001 CLK55; 1992 BMW 850i; 1991 M5
Oh dear... some basic properties of electrical circuits. ( BTW. lower Ohm value == lower resistance)
V = I x R
V= Volts
I= Current (in amps)
R= Resistance (in Ohms)
So assuming the coil gives out a fixed voltage (a few tens of thousands of volts to get a spark in a plug - free air breakdown is about 3Kv per cm before you get a spark - inside a compressed cylinder with fuel and a tight gap it's a lot more!), then *increasing* the resistance will give a lower current path for a given fixed voltage - once the spark starts the plug resistance is negligible, it's all in the wire.
As Power (Watts) is given as W = V x I, then if the current is smaller, and the voltage fixed, the given power is less. (as you've lost some power to the inline resistance of the wire).
I would imagine MB uses 2 ohm leads to reduce the chance of shorting out the ignition coils, and adds some "protection" Adding some impedance also reduces the RF (radio frequency) energy (noise) when the spark fires. Increasing the resistance only adds more "protection", but will also reduce the power into the plug (lower "energy" spark).
Doesn't sound right to put 5 Ohm leads in, as this will reduce the spark "energy".
V = I x R
V= Volts
I= Current (in amps)
R= Resistance (in Ohms)
So assuming the coil gives out a fixed voltage (a few tens of thousands of volts to get a spark in a plug - free air breakdown is about 3Kv per cm before you get a spark - inside a compressed cylinder with fuel and a tight gap it's a lot more!), then *increasing* the resistance will give a lower current path for a given fixed voltage - once the spark starts the plug resistance is negligible, it's all in the wire.
As Power (Watts) is given as W = V x I, then if the current is smaller, and the voltage fixed, the given power is less. (as you've lost some power to the inline resistance of the wire).
I would imagine MB uses 2 ohm leads to reduce the chance of shorting out the ignition coils, and adds some "protection" Adding some impedance also reduces the RF (radio frequency) energy (noise) when the spark fires. Increasing the resistance only adds more "protection", but will also reduce the power into the plug (lower "energy" spark).
Doesn't sound right to put 5 Ohm leads in, as this will reduce the spark "energy".
Now, on a practical matter, what is the real world difference between running a 5 ohm resistor vs. a 2 ohm resistor in a plug wire that is only 6 inches long to begin with feeding a platinum or iridium plug? If the new wires still allow plenty of juice for full and complete spark and ignition in the cylinder, is there any problem with the 3 extra ohms?
It sure seems as though the coils have no problem delivering spark through these wires. The car absolutely runs like a brute. I just don't want to fry an ignition coil or 2!
Finally - why the heck is EVO selling these plug wires as an 'upgrade' if they really aren't as good as the stockers???? I have always found EVO products to be really well thought out and very well made. Its hard to think that they would have completely overlooked this very basic element of a proper plug wire for any given application.
Live and learn, right??
Member
Joined: Oct 2007
Posts: 161
Likes: 5
From: Corona, CA
2004 E55 AMG; 1995 Porsche 993 Cab.
To be honest I'm no expert on plug wires.... High Tension lines are something to say away from, literally!
I'm guessing it's a "look at us, we have something better - it's a bigger number - it must be better"... aka "snake oil".
I would expect you'd see no difference with a couple of ohms... given that it takes 20Kv to make the spark, (and it's the voltage that causes the breakdown and the spark - not the current - the greater current just gives the spark more "energy").
I do know that the BIG and HUGELY important thing is matching the Spark plug operating temperature to the right engine type... there's a good breakdown about spark plugs Heat Range here:
http://en.wikipedia.org/wiki/Spark_plug#Heat_range
Actually, the whole article is a pretty interesting read.
I'm guessing it's a "look at us, we have something better - it's a bigger number - it must be better"... aka "snake oil".
I would expect you'd see no difference with a couple of ohms... given that it takes 20Kv to make the spark, (and it's the voltage that causes the breakdown and the spark - not the current - the greater current just gives the spark more "energy").
I do know that the BIG and HUGELY important thing is matching the Spark plug operating temperature to the right engine type... there's a good breakdown about spark plugs Heat Range here:
http://en.wikipedia.org/wiki/Spark_plug#Heat_range
Actually, the whole article is a pretty interesting read.
