dr bob

We started using platinum and silver-tipped center electrodes in the way-back times on the air-cooled cars, mostly because theye were tolerant of the huge swings in temperature seen between idle and full-load at higher RPM's. The more exotic metals allowed for a hotter tip temp at idle to fight fouling, yet it would still be OK at high loads without erodong at the higher chamber temps. Those that owned early 911S cars, especially the Euro models that were federalized, can relate to getting just a few thousand miles from a set of plugs. After only a thousand miles or so, the engine would run poorly at low RPM's, and act like it needed a new clutch because launches were so jerky. Put a new set of plugs in and it was like a new car again. It was a monthly ritual: New plugs, sync the carbs, check the valve clearance. By three thousand miles of casual driving on a set of copper plugs, the car wouldn't start when cold. Point is, count your blessings that we have better engine temp control (water cooling), better ignition and fuel management, and better plugs. Progress is wunnaful!

chrly924s

I spent many of my days off doing points, plugs, valves, & carbs!!!! Ahhhhh, the nostalgia

Randy V

PM sent, Rog.

siscogts

I found this oltre tread just for a question :
Is someone using ngk triple electrodes, instead the Bosch wr7dtc? It seems that Kindle of Bosch in Italy is hard to find, every parts supplier suggested me ngk BUR6ET triple. Any experience with those plugs? I use ngk only on my old Honda cb 750 four bike... No experience on my car...

R.Pires

Hi,

What is general opinion on when to change spark plugs? Miles done with the car or time they were last changed, even if there is not a lot of miles done?

Thanks you.

Regards

dr bob

My general guidance is based on miles drive, but in fact is better related to total engine revolutions and combustion cycles. The car's don't have tachographs to track that number, so mileage is the next best thing. Just looking at my logbook, mine are at about 25k or so, and probably due for new at this point. There's a set waiting in the parts drawer to go in, it's smoky outside (downwind from several forest fires right now...), and the car is in the workbay for easy access.

----

After reading the Owners Manual when I got the car with 22k on the odometer, I foolishly assumed that the car came with platinum plugs from the factory. When I went to change them at at about 50k, I was surprised to see a set of well-worn copper plugs come out. I'd purchased platinum Bosch replacements sp in they went. The results were less than ideal, evidenced by a marginal emissions test (NOx) result a few months later. So I went back with a new set of Bosch copper plugs, and the emissions results came back down some. From that time, I've been using the Bosch WR7DC plugs with no complaints.

For those playing along at home, most POLAPS (Plain Old Local Auto Parts Stores) seem to have them in stock lots of four. Better IMHO to buy a set of eight matching same-lot plugs from our sponsor vendors just to be sure.

Bertrand Daoust

They're really not expensive so I change them every three or four years.
Maybe 15 to 20K km in my case.

Regular Bosch WR7DC plugs.

siscogts

I changed mine n 2 years ago, i did'know the age of those wr7dtc... Parts store told me that wr7dc were nla... Wr7dc were good also and Bosch second recommended plugs. Here i go after 2 years AND maybe 4 k kms, plug gap is 1,00 mm instead 0,8... You can see are pretty worn. So i went back to parts store and asked for some cross reference. Ngk BUR6ET, copper-nickel (i was told), Triple electrodes... Not sure if feedback about gts+ngk is as good as gts+Bosch...

oups59

I am also using regular Bosch WR7DC plugs. No issues. I changed every 40,000 kms

ROG100

If you own a GTS Porsche used different plugs from 92 to 95. 3 prong plug.

These are current prices.

polecat702

My 89 came with the 3 prong plugs, when I purchased the car from the PO. It's always run great with them, so I never changed them out. Should I switch them to the single prong plug, and a colder plug because of the supercharger?

dr bob

If it's running OK, I'm not sure that changing them will buy you anything. Your '89 has knock sensors so the colder plugs may not be needed with the supercharger. But you may want to go colder so that there's less chance of needing the knock protection.

There are some interesting "features" with multi-electrode plugs. "You don't need to adjust the gap" is the same as "there's no good way to check or adjust the gaps" on a multi-electrode plug. As we get to three- and four-electrode plugs especially, the actual spark area gets shrouded. If you remember some of the electrode-less plugs in the past several decades ("spitfire fire injector" plugs spring to mind...), one of the very few actual benefits was a completely unshrouded spark. The 928 uses an extended-nose plug to get the spark out into the fuel charge, so Porsche was certainly aware of the need to have an exposed spark out away from the chamber floor. A multi-electrode plug reduces that advantage. In my estimation, your supercharged car will do well with a single-electrode plug one or maybe two ranges cooler than what's in there now. A Bosch 6 or NGK 7 or 8 would be a good choice, IMO. Watch the insulator color to see how it's working. You'll tune mixture and timing for best power with a little margin, then pick a plug heat range that works with them. You'll also be carefully looking for the spatter-pattern on the center insulator that's a telltale of detonation.

polecat702

^^^^^^ Thanks Bob, very informative!

WALTSTAR

I dont intend to dumb down the discussion, but I use E3 spark plugs in everything I drive (except the bikes). Before installing them, I checked the exhaust temp from the twin tips. After installing them, the exhaust was noticably hotter. The old plugs were Bosch and not old at all as I installed them when I first tuned the car prior to storage. Just saying that the throttle response is more pronounced as well..

SeanR

I use and put the Bosch 5 or NGK 8 in the boosted cars I mess with. Funny this pops up, we had a guy in one of the FB pages telling everyone that the new Iridium plugs are the best thing to go with. He wouldn't' listen to anyone.