garrett376

Hi Guys - I don't have a new one to tell whether this plug is pitted/worn or not. It's hard to get a good picture, but from this view shown below, the center electrode is NOT circular, it has slightly flattened spots towards each of the three electrodes.

Is it supposed to be circular?

And question #2 - does everyone use these fancy 3 electrode plugs, or does a single electrode plug work just as well?

Indycam

It starts out round and gets spark eroded over time .
I've never seen any others vs the 3 electrode type .

garrett376

Ok, that's what I thought - time to order yet another part!

One of my C4's came with regular, single electrode plugs installed when I bought it. I guess someone was being cheap, eh?

Indycam

Your plug looks fine , are you getting more to replace them ?
Are you getting a misfire ?

garrett376

The engine runs just fine - actually runs fantastic - I just have no idea when they were last replaced, and this car needs a little catching up on the "little things" with regards to maintenance. I think the owner's manual says every 12,500 - 15,000 miles to replace them... I just have the engine out so access is so easy at this point!

garrett376

Here's a better pic - it's hard to focus the camera this close!

Indycam

I am a cheapo , I don't replace plugs until they are useless . If I had a set of plugs that look like that and work fine , I would not spend a dime .

ttAmerica RoadsterAWD

Looks like your engine is running fine based on the color of the plug. With respect to the plugs life, there needs to be sharp edges between the cathode (center) and the anode (three prongs). Typically the spark plugs have run their usefull life for optimum performance when both anode and cathode have rounded surfaces at the spark areas. If they are rounded, they will still work, but just not optimally.

Jaime

Indycam

"If they are rounded, they will still work, but just not optimally."
If they are rounded will the spark jump the gap ?
Will the spark be smaller ?

Geoffrey

The factory plugs are not performace plugs, but anti fouling plugs. There are better options.

Here is but a sample of spark plugs available for the 993 engine. From left to right

Denso irridium .4mm electrode
NGK irridium .7mm electrode
NGK irridium .7mm electrode (JIC length)
Denso double platnum 1mm electrode
Champion racing nickel 2.5mm
NGK replacement plug triple ground strap
Bosch replacement plug triple ground strap
Beru replacement plug triple ground strap

springer3

Be careful. This could be false economy, because degraded plugs need more firing voltage, and that adds stress to the insulation, coils, and the electronics. Better to replace cheap plugs than risk damaging expensive parts. That being said, I would re-use Garrett's plugs. Set the gap using a pin gage, and get all three electrodes even, and you should get another 12,000 to 15,000 miles.

TT America had an Interesting comment on sharp versus rounded edges. The rounded rings you see on high-voltage equipment are called corona rings. They are designed to prevent the corona discharges that precede the electrical breakdown of an air gap. Retard the onset of corona, and the spark-over voltage goes up, all other things being equal. The size of the air gap is the most critical parameter. As long as your air gaps are OK, you should still be fine with eroded corners and edges.

ttAmerica RoadsterAWD

The tripple anode serves to provide an aleternate route of fire when one of the cathode/anode surface is not optimal. As has been explained to me, the triple anode fires only at one anode, not all three simultaneously. Having alternate routes helps against misfires. Given identical gaps, electrical flow is facilitated by sharp edges and hindered by round edges. This, however, can be overcome by higher voltage.

Jaime

last toy

Since you have the engine out anyway, I would replace the plugs with high performace ones and avoid the hassle down the road. You could clean and square off the anode prongs and probably get another 15k miles on them if you can set the all 3 gaps exactly as specified which may be very difficult. For the cost, it's worth taking the plugs and maybe even the wires out of the equation when measuring performance.

garrett376

Followup time!

I ended up ordering new plugs even though I decided later that I'd just keep the plugs. You can see from the picture below that the electrode is originally round, and my plugs look worn beyond what I want.

That answers my own question - that the plugs are due for replacement!

garrett376

here's a comparo: