Proper Spark plugs for Motronic Carrera Series, '84 to '88 - resistor or nonresistor?

[movin]

1) Should Carrera's use a resistor or nonresistor spark plug? Thought I heard someone say because the system is electronically controlled and may be sensitive to EMI, you should always use resistor type spark plugs. Is this true? Is there any detectable difference in performance between nonresisitor and resistor plugs? If not why bother with nonresistor type which are sometimes hard to find at the local auto supply stores.
2) How about plugs with cut-back ground electrodes, (racing type), do they offer improved performance too?
Thanks!

[RickM]

Bosch part# for OE Carrera plug is WR7DC. R is for Suppression Resistor.

[Rot 911]

Did you mean to start a new thread for this?

[movin]

Yes, I have a question about the resistor issue and so-called
cut-back plugs which are available from a number of manufactures, or the mod. that can be done by cutting the ground electrode.

[RickM]

Interesting...learn something new every day. I'd imagine they'd need to replaced more often as well.

From Champion:

"Cut back ground and angled ground electrodes both improve performance by exposing more of the air fuel mixture to the flame nucleus and reduce quenching by limiting the available contact(surface) area between the electrodes and the flame nucleus. "

To add from Sparplug.co:

"They are also called by a variety of names depending on manufacturer, IE: trapezoid cut ground, tapered cut ground, fine wire ground, angled ground, trimmed side electrode, wedge shaped ground, inverted V-tip ground, cut back ground, etc. All have the same purpose, to reduce quenching and shadowing."

Angled


Cut


Standard

[kach22i]

Is there a trick to gaging those angled plugs?

[stlrj]

It's not the plugs that we should be concerned about since they all do the job, but getting the spark to them using OEM copper core igniton wires.

Now that's the Achilles heel of the 911 ignition system.

[johnnyo]

I just purchased a set of Nology hot wires for my 911 anyone else have good results with these?

[Porsche_911s]

From what I have read most here on the board do not like or recommend the NOLOGY hot wires.

[Thrasher]

Seems there was never a definitive answer on Resistor or Non-resistor on the 3.2

I ask because I just pulled my Bosch W7DC (NON-resistor) plugs. They look perfect. Just a slight sandy-brown residue, no carbon.

BUT, I read in my manual that OE are WR7DC (or WR7DP if you want platinum) ... so I will repeat the original question:

Why would the PO's wrench have put in non-resistor plugs, and, given that they are working so well, should I not stick with them?

[Rot 911]

Originally posted by Thrasher
Seems there was never a definitive answer on Resistor or Non-resistor on the 3.2
I ask because I just pulled my Bosch W7DC (NON-resistor) plugs. They look perfect. Just a slight sandy-brown residue, no carbon.
BUT, I read in my manual that OE are WR7DC (or WR7DP if you want platinum) ... so I will repeat the original question:
Why would the PO's wrench have put in non-resistor plugs, and, given that they are working so well, should I not stick with them?

Craig the heat range is the same on both plugs. The resistor plug just does a better job of reducing electrical interference such as buzzing on the radio when the engine is running.

[Thrasher]

Ok, that's what I thought. I'll stick with a resistor plug then.

BTW, if anyone is buying plugs, there is a $1/plug rebate on Bosch Platinum until 6/1/2006 - just go to www.boschusa.com/AutoParts/Promotions/PlatinumRebate/

I doubt there's really a performance gain, but they cost about $1 more than copper and probably have a little longer life. Can't hurt, right?