ViribusUnits

The 2, 3, or 4 prong electrodes are not "gaping free." Instead they're "gapping impossible." Sorta like "maintance free" batterys. I personaly belive that most of the problems with the 4 prong electrodes going into cars that we're not origionaly designed for them is that they have the wrong gap.

The 928's ignition system is an inductive discharge system designed for a specific gap in the combustion chamber. Inductive discharge systems are something of an inbetween system. They are more powerful than a traditional points system, allowing higher voltages and amprages to the plugs, but load up the plug more slowly than a capasative discharge system. This makes them better than the traditional points system, but not as good as the capasative discharge systems.

The big short fall for the industive discharge system is that it doesn't ramp up the current as fast as a capasative discharge system. If there is a bit of fouling on the plug, it is possible for it to bleed off some of the stored up energy in the coil, preventing the plug from fireing. A capasative discharge system generaly ramps up the current faster, and stands a chance of overloading any small amounts of fouling, and fireing the plug anyways.

Fouling is only a problem on 928s that aren't run hard enough. The plugs never come up to temp, and thus never burn off the excess carbon, or oil, or gasoline residue, etc. I generaly run the hell out of engines on hot Texas days, so I've been known to errode the platinum tips of the plugs. The platinum plugs won't react with stuff in the combustion chamber, but it's melting point itn't all that high, which seems to make it easier to errode the center electrode.

One final note, unless you've got two coils, you will almost always only have one spark path. Once a spark jumps, it set up an ion trail, and all of the electricy goes through that one pathway. Generaly the ion trails only go from one electrode to one electrode.

I'd say just run the correct heat single electrode plugs.

Anyways, YMMV.

CMW

No issues on the 89 S-4 for 3 years.

I do not use them on the S/C GTS

The Bosch Plat +4 seem to prefer some 928's and not others. (now that I have read B Webbs post what he said)

PorKen

We don't get the good stuff here! Just gimmicks. You have to go to the european Bosch sites to see the 'Super 4':


clic pic for site

I bought the factory spec'ed plug for '81 - WR8DS - Bosch Silver (single electrode, single anode, silver plated copper). They were about $5 each, but they show almost no wear in 3 years running.

Doug Hillary

Hi,
I have used Bosch Platinum plugs since the early 1960's in a variety of engines - mainly German

Electrode design is closely related to combustion chamber and ignition system design, Bosch do not even make Platinum plugs for some BMWs and VWs for that reason

The 928's recommended single electrode Platinum plugs - W7DP - work well in the 928

The GTS came new with a twin electrode plugs as standard I believe

I have had nearly 50kkms on W7DP plugs in two 928s - totally trouble free

Regards

morganabowen

I had them on my '82, and it ran very rough. Replaced them with the regular platinums, and the car ran just fine. I gave them to the person that I sold the car to

deliriousga

Now that makes sense and kind of explains why they work for some and not for others. I run my 928 hard (keep her over 4000 while cruising) to burn off the carbon deposits and help keep them from forming. She runs much smoother and sounds sweeter that way (less clicking/clacking, etc.) That's probably why the Bosch+2 work well in mine and not in some others. I'll have to watch for the errosion as mine have only been in the 928 for about a month. Thanks for a great explanation.

NickT

Interesting thought to cruise at > 4000 RPM..

Mongo

I have them and after about 7,000 miles I've noticed my car running richer with popping in the exhaust when it never did it before....then again I just put resonators on so that could also be the case.

deliriousga

I'll qualify that. Not "cruise" as in driving through a parking lot 50 times in a night.

No, really, I don't take her above 3000 until at operating temp, but once there she's rarely under 4000 rpm. That's one thing you gotta love about a Porsche. 4000 rpm and she says "aaaaahhhhhhh yesssssss!" any other car and it's "oh sh......."

Bill Ball

I ran platinum +4 for 4 years and 70K miles in my 89 S4 until a recent change. The plugs worked perfectly and looked new when removed.

Schocki

I run Bosch "Super 4" in my Euro GTS they are sweet they last much longer than normal plugs and the car runs good with them. Platinum plugs are just more expensive (Just my opinion).

Mark

JUST SAY NO!
THe standard Bosch Super's are all you need.

I have seen a 928 and a 911 engine really screwed up when one of the electrodes burned off and fell down in the cylinder!