FisterD

We use Bosch FR5 DTC.

vincer77

Thanks for reviving it. I get to relive some of the history of my car!

Slow Guy

See Vince, I used the correct plugs, even if only by accident!

Seriously considering doing plugs on the coupe this winter so thanks for the reminder.

s4for5

Did you really re-gap the 3 electrode plugs?
To what spec?
The same as single electrode?

P-daddy

Hey Bill, have you put on 30K since last time? Or you're changing them based on time?

Slow Guy

Yes, I'm one of those that does check the gap on 3 electrode plugs. I have a few wire-style gauges for this. I don't try to get them exact but I do want them between the .7 - .8 spec. I don't order extra plugs just in case some are smashed since I only order for my car.

Different car. Vince has my old '97 Cab and I now have a '97 Coupe since I started this thread. I have put on almost 12k mi. on the coupe in the 2 yrs I've had it though.

geolab

To reply to the main question, after my curiosity questions answered along the years

Why two spark plugs:
compressed air fuel forms two pseudo bulbs-clouds if not ignited at piston drop down after top compression. So two spark plugs is two ignitions at two places thus more efficient combustion, cleaner etc.
As per bosch engineer, two spark plugs (also) permits the use of cold spark-plugs instead of one hot spark-plug thus less cylinder head heat.
Turbo with one spark plug? yes, HOT spark-plug but cooler air from intercooler, lowers head temperatures.
Could we use the turbo hot spark plug in the NA engine, yes, but it is advised to use the cold spark-plugs

Why three electrodes:
because ceramic is bad heat conductor, the three electrodes makes the spark plug tip have a larger contact area and transfer more heat away from the spark plug tip.
So bosch FR5 DTC has a different heat range than the Beru 14FR6LDU
If someone knows somebody different at bosch to confirm, would be great