There has been extensive discussion on the Rennlist about this topic, but I am copying Steve Weiner's comments below, as he has a great deal of experience in this area:


Dan & Chris raise good points about those excellent, but dreadfully expensive, Bosch DPO plugs. This needs to be put in context, though.......

These plugs were developed by Bosch back in the early sixties to address plug fouling issues with the inherent rich-running MFI systems, just as Dan wrote. The best technology of the day; Bosch CDI ignitions were much better than the normal Kettering point/coil ignition but they still didn't have the output to keep plugs clean until the advent of the modern high-output multi-sparking ignitions like MSD & Crane.

We now know that wide plug gaps (.040 or greater) virtually eliminate plug fouling, really enhance idle quality and drivability, and make more overall HP (on the dyno) IF,...........................IF the ignition system possesses enough voltage & current to start and sustain a spark across such a wide gap.

The family of OEM Porsche ignitions (Bosch-Permatune) systems do not really have the output to do that and thus, for those people using stock ignition components, the Bosch DPO platinum plugs have been a partial solution. There is a better solution,........

For people willing to use a much, much improved ignition system;
installing the MSD-6AL and its matching impedance coils, you will be amazed at the difference in overall running when this upgrade is made and the plug gaps are opened up to .040. You can use any plug (Bosch-NGK) you want, not just those spendy Bosch DPO ones,...

BTW, This works really well for carbureted cars just as well.

I would simply caution anyone who does this to ensure that the rest of the system; distributor cap, rotor, plug wires & connectors is in perfect shape, too. IMHO, you are well served by using the 8.5mm Magnecor wires to eliminate the troublesome Beru connectors with those internal resistors that fail all the time.

I hope this helps and clarifies some information on this subject.