davek9

And.. if your running N2O or any other Hot application where you want to avoided "hot spots" it the combustion chamber then look to a Non-Projected Spark Plug.

dr bob

I wouldn't replace them just because they are different. If the car runs OK and passes smog, leave 'em. There's just no need to spend on them. Look at how fortunate you are! Set of 8 Bosch Platimun Plus-4's at a reasonable price, and they came with this cool car!!

The Forgotten On

It also came with a recently done TB job with no service history at all before I bought it.

I guess the general consensus here is to get stock plugs from our main sources and not waste money on spark plugs.

dr bob

There are plenty of "gimmick" plugs on the market. There are more exotic plugs for more exotic purposes. Our US cars that don't see track time generally live a very stable life as far as combustion temps. Contrast to a now-vintage 911 I had back when it wasn't 'vintage'. It ate plugs for breakfast, lunch and dinner if I wanted it to play well all the time. Cams and carburetors worked together to have a bit of intake dilution at idle and low speeds, so some functionally lean misfiring. Being air cooled meant that temps could be anywhere, so finding plugs that would last was almost the holy grail. Tried lots of flavors of Bosch, some Beru, Lodge, and even NGK, looking for the perfect plug that could be street-driven yet not all flat from fouling and deposits when asked for more. Electronic CD ignition was the first leap forward, and ultimately cars with electronic injection were the daysavers. To this day there are folks who still swear that carburetors were better. They probably were better than some of the early FI systems. Big V8 MB cars from the late 60's or so had a Kugelfischer mechanical injection system that was a joy when it worked and an absolute nightmare when it didn't. Fortunately those cars were generally sold to folks who cared little about fuel consumption. Pumps and nozzles were Diesel derivitives, metereing was similar but didn't do that well with gasoline and metered air. Good stuff! Eventually sold to Bosch and then retired.

Tony320

So the copper plugs are the "colder" of the two, and less likely to cause detonation?

ROG100

I advise all my customers to use the spark plug as specified by Porsche.
If the car is modified then change to what meets the challenge.

WR8DS are the stock plugs used in 80 to 84 cars.
Different year car uses different plugs.

dr bob

Sort of. The platinum or silver plug in the same heat range will have a hotter tip. There's a potential to cause pre-ignition if it's too hot. That's different from detonation, but they can be related. Detonation is the uncontrolled explosion of a fuel charge, as opposed to the relatively slow burn you really want. Pre-ignition happens when the charge starts burning too soon, perhaps from a hot spot in the chamber.

vernon

I bought a set from Roger an the old plugs where bad the new WR8DS are very good an my car runs very nice now. Thank You Vernon

Tony320

Thanks for the clarification gents.

linderpat

Roger - what should I use for a 78? Here are a couple of pictures of what I have now, bought a year or two ago, and it looks like the plug is burned all the way down. They are Bosch Platinum WR80P.

ROG100

I have always had issues with Platinum - do not know why but they do not seem to work well in a 928.

Porsche specifies 999 170 170 90 for your car = WR8DC+ (I sell for $2.25 each)

linderpat

Roger - please send me 8 of them. Thank you!

dr bob

Ed -- that's a standard look at a platinum plug. The tip is shrouded by the insulator. With the platinum metal able to stand higher heat than the copper, the insulator is longer, with more exposed to combustion relative to the area that allows heat to pass through the shell to the head. It's hotter, and less likely to oil-foul or retain fuel deposits.

On the plugs you show, grab a magnifier and look at the corners and edges of the ground electrodes. If they are still sharp, you can clean and lube the threads and re-use those plugs. From what wear (arc erosion) I can see in your pictures, those plugs have maybe 10k miles on them against a typical 40-50k expected life. Or spend the $20 on new DC's.