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Old 06-20-2006, 12:54 AM   #1
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Default Proper Spark Plug Condition

I have a 92 miata. greddy kit, vortech fpr, high pressure fuel pump, no intercooler and I'm running 7 psi thanks to a aftermarket wastegate. When I put my turbo in I re-gapped my plugs to run a bit colder, I've put about 1500 miles on since the turbo install and did the plugs at the same time. I just checked the plugs and they looked fine I think. The tips were brown and they weren't really dirty. I would almost call them rusty, but they were rough, just smooth brown. Is this normal? Just want to know what they plugs should look like and what I should be watching out for with a turbo car as for signs in anyway of a possible problem
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Old 06-20-2006, 09:14 AM   #2
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I recommend getting the proper colder range plugs (part number can be found on this forum... I've seen it but I'm too lazy to search and link). Closing the gap isn't a good idea as it lowers your combustion efficiency. Generally speaking the bigger gap you can run the better.
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Old 06-20-2006, 09:32 AM   #3
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First off, gapping a plug down does not make it a colder plug. A colder plug has different insulator size and electrode tip lengths than the "regular" plug.

Secondly, reading a plug is extremely difficult unless you run several full-boost runs to redline then shut the car off immediately. Otherwise, the plugs have too much time under normal operating conditions to really tell you anything.
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Old 06-20-2006, 10:01 AM   #4
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Old 06-20-2006, 03:55 PM   #5
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As stated earlier the gapping and heat range are two different things.

The gapping has nothing to do with running any colder. Usually the plugs are gapped a bit closer so they fire better thru the increased resistance of the additional compression. At 8 PSI boost, I set gap at .035. Would be a better advantage to go slightly wider for different systems. That would be trial and error for optimal gapping on your system.

"Colder Plugs" merely means there is less insulation on the tip. The secondary function of the spark plug is to alter heat in the combustion chamber. The colder plug extracts more heat from the combution chamber where it is removed by the cooling system. They may or may not be needed, depending on your driving contitions, style, and efficiency of the cooling system.

The best way found to see what works best is to use new plugs, go for a hard 30 minute romp, then check the faint tint on the plug. Can do the same with experimental gapping to see at what gapping eliminates any misfire.
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