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DLF
10-08-2009, 12:58 PM
These look pretty good to me, anybody else have an opinion?

S_Mazza
10-08-2009, 01:13 PM
The two in the upper right look they might be oily, but otherwise everything looks normal to me.

KMT
10-08-2009, 07:39 PM
What type fuel you burning? Any ethanol?

They look generally ok otherwise I think.

DLF
10-08-2009, 07:49 PM
Nope, just 93 Octane.

Hock
10-09-2009, 12:15 AM
I think they look ok.

XR7 Dave
10-09-2009, 12:57 AM
You can't read plugs after they have been in the motor for a long time as a variety of conditions will taint the porcelain. Those plugs do have a lot of color on them, but if you've run race fuel in the car at all then that may explain that. Pump gas normally leaves the plugs pretty well clean. To really read the plugs you have to look down at the base of the porcelain with a Dr.'s ear light, and it has to be done immediately after a full throttle run on new plugs.

About all you can really do with a plug that is old like that is to look for signs of detonation and check your heat range. Those particular plugs should never be used in a performance application because they have highly extended tips which is just plain bad news.

DLF
10-09-2009, 01:29 AM
You can't read plugs after they have been in the motor for a long time as a variety of conditions will taint the porcelain. Those plugs do have a lot of color on them, but if you've run race fuel in the car at all then that may explain that. Pump gas normally leaves the plugs pretty well clean. To really read the plugs you have to look down at the base of the porcelain with a Dr.'s ear light, and it has to be done immediately after a full throttle run on new plugs.

About all you can really do with a plug that is old like that is to look for signs of detonation and check your heat range. Those particular plugs should never be used in a performance application because they have highly extended tips which is just plain bad news.

I appreciate the comments. Why are you concerned about the extended tips? Detonation? I've never had a problem, but I've only got about 300 RWHP.

What plugs would you reccomend?

89XR7TD
10-10-2009, 11:35 PM
I think Dave is implying that you should run a colder plug like autolite 103's with less of a gap and can run more OD.

But I could be wrong.

Tom

XR7 Dave
10-11-2009, 08:56 AM
I appreciate the comments. Why are you concerned about the extended tips? Detonation? I've never had a problem, but I've only got about 300 RWHP.

What plugs would you reccomend?

Extended tips are there to promote a cleaner burn when running at leaner AFR's and light loads (basically emissions). A lean mixture combined with low compression doesn't burn very well, this is the whole reason for the "MSD" theory and is why some Ford systems also have a multiple spark feature. None of these system fire multiple sparks above about 3000rpm and therefore have no impact on performance above that threshold. An extended tip spark plug like that one not only has a long electrode, but the ring of metal that doesn't have threads, protrudes into the combustion chamber. Remember that the cooling of the tips is performed by the contact of the threads with the cylinder head. Having a lot of metal protruding into the combustion chamber means you have a lot of mass exposed which can hold a lot of heat. If the very end of the electrode doesn't cool sufficiently, it can turn yellow and cause auto-ignition under high rpm/load. Auto-ignition in a supercharged engine is almost always fatal (melted pistons, cracked ring lands, bent/broken connecting rods, or blown headgaskets). You will rarely encounter auto-ignition where physical damage does not result so it's not something that you "have a problem" with unless your motor is no longer running (well). There aren't typically 'degrees' of auto-ignition, you either break something, or you didn't have it and it typically doesn't give a lot of warning so it is best to avoid it at all reasonable costs.

Detonation on the other hand is not caused by a hot spark plug. Detonation always occurs opposite the plug because detonation always occurs after the spark has already formed. Detonation occurs after normal combustion generates enough pressure to trigger a second ignition event, and this almost always occurs at the intake valve or under the quench pad, never at the spark plug. All SC engines are prone to detonate to at least some degree, but detonation is not usually fatal and isn't always audible either so you will not be aware of it until it gets fairly severe. You can look for signs of detonation at the plug. If you run clean plugs, you might find tiny spots of oil on the plug, or you might see erosion of the insulator around where the electrode pops through. With plugs that are old or have lots of deposits already, it is harder to see this. When running a performance supercharged engine one should always closely monitor plugs. I suggest putting in a new plug and running it at the track, then pulling them out to see what you find. If all is well then put them back in and run them no more than 10K miles and then pull them out and put new ones. I would always do this before a good thrashing so that you can pull them out and check things again. Your spark plugs are your window into your motor and should be watched closely. I know some people who change their oil at 2x the recommended interval, but don't know of anyone who changes/checks their plugs often enough. Well, maybe a couple. :p

Heat range is important too. You can observe heat range by looking at your ground straps and looking for discoloration but again, this should be done after racing or running the car hard. A variety of conditions encountered during normal operation will taint the results of this performance check. Making sure that the plug is cool enough to stay far away from auto-ignition is important. If you look at the plug that Ford used as OE on the 03/04 Cobra, you'll get a good indication of the type of plug that should be used on an SC. The plug they use cross references the Autolite 103 (been recommending that plug for years). There are cooler plugs yet for competition use but they may foul under light load conditions (like extended idling).

Under normal use your plugs should not be colored like that, even though that coloring is not bad, it shows that they have been in there too long to read anything useful off them.