what is the best plug for a 1985 928s us?
What is the difference between Bosch Wr7dc+
and Bosch Wr7dtc

 

The DTC is a three pronger not all that good as a performance plug. The standard single copper plug works best might need to be changed slightly more often but still the best running overall.

 

What is the correct gap on the wr7dc?

 

0.7MM +0.1MM..., from my Porsche tolerances booklet

Ken
80 928 S
5 Speed

UK

 

What is the difference between the wr7dc and the wr7dc+?

 

Actually, Porsche runs this style plug in all of their factory race engines.

The fact that there are three different electrodes allows the gap to remain constant over a much longer period of time.....making ignition far more consistant.

 

Interesting. So is the DTC a better plug for 928's? Or stick with the WR7DC style plugs?

 

The DTC was used on the GTS cars from the factory. Still available from Porsche circa $9 each or NGK BP6ET for $4 each. I use these in my GTS but use WR7DC+ in my other 87+ cars.

 

The heat range and the characteristics of the plugs are virtually the same.

For a street engine, probably depends more on how long you want the plugs last. Porsche started using the DTC plugs when the service intervals for spark plug changes got longer. In the race engines, this plug also made sense, because the multiple electrodes kept the "spark jumping distance" similar, longer.

If you change your plugs every 10,000 miles, use the cheaper plug. If you want to increase that interval to 20,000+ miles, use the DTC.

 

Note to self: Change plugs...

Thanks, Greg!

 

I use single electrode plugs because they are easier to gap.

 

I would lthink the triple prong would be very difficult to gap...

andy