Resistor Plugs

[lr172]

I am going to colder plugs to accomodate my turbo. I naturally bought resistor plugs (BPR7ES) to protect the EFI. Then I reliazed that I also have resistance built into the rotor. It appears that a resistor plug (WR7DP) was spec'ed for this engine. It made me wonder if I am taking too much current away from the plug and minimizing my spark energy. I know that most US cars do just fine with just a resistor in the plug and a straight through rotor.

Does anybody know if the resistor in the rotor is helping or hurting?

I use a Blaster II coil fired by the EFI. This is comparable in specs to the stock coil.

Thanks,

Larry

[stormcrow]

lr172

Do some research on the plugs. I am pretty sure the "R" in the WR7DP means resistance just as the "R" in the BPR7ES means the same.

The difference between a hotter plug and a cooler plug is the thickness of the ceramic covering the end of the plug electrode

SteveKJR

"A Porsche does more then just go fast in a straight line"

[lucittm]

I talked to a Bosch guy about resistor plugs because I wanted to understand the purpose of the resistor. I know what a resistor does in an electronic circuit, but not a 50KV short circuit to ground kind of application.

He said that regardless of what you use to create your spark: CDI, battery and coil, or MSD, there is electrical noise that "rides" on the high voltage created by the switching of transistors, diodes and even points opening to collapse the stored power in the coil. He said the purpose of the resistor is to clean up some of the noise that rides on our spark voltage. He called it the tip of the dragon's tail. The voltage is still there, but the last bit of the trailing edge of the electrical power drops of more cleanly with the resistor in place.
Everybody uses them, dragsters, Indy cars, Formula 1...

So, I stick with my WR6DP0 plugs (slightly colder than your WR7DP) and now I know why there is a tiny resistor in there.

What kind of rotor do you have? I'm sure if there is a resistor inside, it will cut down on the arcing at the edge of the rotor.

Mark

[T77911S]

i would try a WR4 or BPR6 first or colder. start cold, work your way to a hotter plug. if mixture and timing are correct, look for plug fouling (cold and/or idling problems) and check the plug for "self cleaning" every so often. a too cold a plug does not get hot enough to clean the carbon off and too hot a plug can melt, some say it will not cause detonation, soem say it will.

if it was not for cold starting and rich idling, you could run a colder plug than normal. i tried a WR4 in my 2.7. on a long trip it stayed clean, lean burn mid RPM range, but once i was driving it around town, the plug got black from more low RPM and idling.

[Flieger]

I always went with the advice to run the coldest plug you can that does not foul.

[RoninLB]

Originally Posted by lucittm

He said the purpose of the resistor is to clean up some of the noise that rides on our spark voltage. He called it the tip of the dragon's tail. The voltage is still there, but the last bit of the trailing edge of the electrical power drops of more cleanly with the resistor in place.
Everybody uses them, dragsters, Indy cars, Formula 1...


What kind of rotor do you have? I'm sure if there is a resistor inside, it will cut down on the arcing at the edge of the rotor.

60 years of resistor plugs technology effect on its use in a 2 or 3 page setion of a Peterson article. They were first used to prevent the tip of plugs from burning off from that "tip of the Dragon tail"