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Lightbulb Interesting Spark Plug Article

Found this in the Tech Article section


Spark Plugs

I have been using three electrode Bosch plugs for years. They are specified on the 911 3.6 liter Carrera and 911 Turbo. What is really surprising, is the increase to a warmer heat range. The early 911S and all Turbos used a ridiculous cold and expensive W3DPO spark plug. This little plug costs about $16.00 each and I have never removed one that wasn’t dark and sooty (indicating too rich or too cold of a plug!) Tuners of these expensive Turbo and early 911S cars were, and are, reluctant to vary from the factory specifications. This is a problem. as Porsche can not respecify the older cars without recertifying the whole engine emission certification all over again. Porsche is not likely to do this.

What is interesting though, is what has happened to the 911 Turbos. The trend became to increase the power output while meeting tighter emission standards. The compression ratios were increased to 7.5:1(from 7.0:1) and even without knock sensing using a much hotter spark plug, the FR6LDC. This is a copper core, double ground electrode mini spark plug. The fact that the Porsche factory specifies this very warm spark plug for the awesome 3.6 Turbo is not so difficult to understand. I have talked to Bosch, BERU, and NGK about their new applications for old W3DPO spark plugs, and have been told that those were really too cold — even for a street Turbo. The factory originally specified them in the same way they specified spark plugs for the special 356 Carrera 4 Cam, 911 S, 2.7RS and other higher performance "street" Porsches. The factory expected these owner drivers to run the daylights out of their Porsches and they did not want the engines to "ping" and detonate from using non-German gasoline. So they specified cold spark plugs. It worked. The 911 Turbo came along at first as a batch of 500 only, to be sold originally for "Friends of the Factory." They got the same treatment as the earlier specials. Nothing changed until 1992.

The 3.6 Carrera has used Bosch FR6DTC triple electrode since 1989 and these run great. I started using these 3.6 spec spark plugs in just about all 911’s and have had excellent results with them, especially in my own hard run Turbo motor. I will keep my pile of old "W3DPO", but only for competition events.
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 04-06-2007, 03:12 PM
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