SeanR

Fred, here's a link to a discussion on the GTS plugs.

https://rennlist.com/forums/928-foru...ark-plugs.html

ROG100

Hi Fred,
I only recommend the plugs that Porsche specifies - all 87 to 91 use the WR7DC+ copper plugs – Bosch 7900. This is a single prong plug.
92 to 95 cars used the three prong plugs – yes I understand prongs 8>)

I will NEVER use anything else - especially the 4 prong platinum plugs. I was once recomended to use them but once I changed to the correct Porsche 3 prong plugs in my GTS I noticed a difference.

I am assuming the cars are basically stock - if modified that is another question.
Best,
Roger

FredR

Roger,

I was also recommended ot use the 4 prong plug and never felt as though I have a problem with them but then I have never done any back to back testing. I did my shark tune with these plugs fitted so I am some way off stock as it were. The engine can hesitate a little off tickover when "coldish" for whatever reason but I put that down to the various mods I have done in ST2. Generally the engine revs very sweetly and smoothly these days and starts first time every time so never feel a need to do anything more. If I want to pull away sharp from the lights I keep my keft foot on the brake pedal and gas to 2k rpm before taking off. Seems to work quite nicely.

Regards

928mac

I like the way you think in your signature

dr bob

Some thoughts--

Platinum plugs are popular with cars that have trouble with plug deposits. The platinum wire can withstand higher temps so a slightly hotter tip is used to burn off deposits. Downside is that the tip temp is hotter so there's a small risk that it will be a hot spot, enough to start a flame before it actually sparks. Not a serious problem in later cars but can be that tiny difference in passing NOx on marginal cars.

Multi-electrode plugs are used solely to get extended life. Car mfrs are forced to warranty engine pollution parts for 100k, and they don't want to have to put new plugs in under warranty. These plugs are expensive, and virtually impossible to gap correctly and evenly. The additional electrodes shroud the nose where the flame starts.

For most of us enthusiasts with well-maintained fuel and ignition systems, the copper plugs work fine. They are readily available, reasonably priced, and they work fine. I pull the plugs once a year to inspect for uneven color, put the same plugs back in unless there's a problem. I'm on my fourth set in 100k on the car. I usually replace the oxy sensor at the same 25-30k interval, to give you an idea about how often they get all get replaced. 5 years or so between changes, annual look at them.

*****

Plug vendors will often tout how their plugs improve mileage, performance, driveability. They forget to say that they compare their plugs new with the worn-out plugs that were in the car. At 25k, a new copper plug will give the same benefits as a new super-wamadyne-unobtanium-tipped $21 miracle flame injector plug. Save your discretionary toy money for something that really helps.

Rob Edwards

I just changed the spark plugs in my mother-in-law's '95 Corolla, after 112,000 hard charging miles- pretty sure they were original. Gap spec is 0.032", these measured 0.088.... Car runs somewhat better now!


Looking through the service records, my GT had the plugs changed by the dealer at 15, 30, 45, and 61K miles. Then it must have dropped out of warranty... Greg Brown has mentioned hat he feels 928 plugs have a 15,000 mile lifetime, and at ~$2.25 per, why not? He put the standard WR7DC coppers in my stroker.

blown 87

We had a late model Ford in the shop a couple of weeks ago and the side electrode was almost all gone, the center electrode was actually recessed down in the Porcelain almost a 1/16 of a inch.
I was shocked that one, it went that long, two, that the plug actually came out, and three that the coil pack went that long before it said "ENOUGH"

blown 87

Some cars, Volvo's for one, will turn the check engine light on with the 4 prong ones, I do not know why, but they will.

WallyP

I changed the factory Autolite plugs on a Lockheed engineer's car years ago that had the center electrode recessed into the insulator, and ground electrode half-gone. He sheepishly admitted that the plugs had never been changed, because it still ran OK at 95,000 miles.

17prospective buyer

PO for my 87 S4 used NGK's... I think that's part of the reason it was/still is running too rich. Well, running with not enough spark i should say... Can someone tell me how those Nology plugs are? They tout alot of exclusive proprietary technology, but are they worth it? I was thinking of just getting the whole she-bang with a 928 Spec. tune up kit. The electrode on the NGK was like paper thin when i checked it. Could oil cause this? I do have leaky cam cover gaskets, as the plug threads were covered in clean looking oil.

Mrmerlin

17 use the Bosch 7900

FredR

The only poblem I see with the multi prong plugs is gapping them [if you have to]. I do not do a high mileage in the 928, quite the opposite [10k km max per annum] and the four prong plugs are still fine after nearly 5 years in the current incarnation.

I did have a problem once when my late red 90'S4 was in the local dealers- for some reason they removed a couple of plugs and when I picked up the car it had a misfire so we removed the plugs and found one had a bent prong shorting out probably casued by dropping the plug free fall into the socket! I just pryedthe prong back into positionby eyeball measurement and it ran just fine.

Glen- good to see you appear in good shape. I seem to remember I also had a problem with data logging initially in that sometimes it would log and sometimes it would not. One of the things we did on John's recommendation was to install a jumper between two resistors but unfortunately I cannot remember if that was the root cause of tha problem. All being well you will have everything running as it should in no time.

If you are on std injectors running a lightly modified setup then just take a good sized data log and load it on Jim's shark plotter programme and then adjust the cell values to get the afr you target for that load range. You will invariably find that a mix of part load and full load runs do not occupy that many cells in the total matrix. Once you have sorted out the AFR you can then focus on timing enhancements but doubtless John and Jim will have pointed you in this direction already
Regards

Fred

FredR

Oops= got posts mixed up-ignore last para- belongs on another post from Glen [its past my bedtime]

Fred

Fortuna

Hi!
How do I register on the website 28srus.com?
In the registration of the delivery address (Invoice address) to the U.S.

SeanR

There isn't any registration, just send him an e-mail. 98% of what he sells isn't on there.