Greetings all.

I have been running NGK Iridiums (BR8EIX's gapped to 28 thou) in a 2 liter turbo at 1 bar. The plugs have been a bit dark but I have not had any fouling or engine miss issues whether at light cruise or WOT. They have been in for about a year and other than a little carbony look good.

I recently changed plugs and went a step warmer and went to coppers, BR7ES's. During light cruise I get an occasional miss but WOT is fine. Plug color is much better than the 8's. I started with a gap of 24 thou and opened it up to 28 and it still misses. To see if the coppers were the problem I put the Iridiums back in last evening and went for a drive and the misses were gone!

Hmm... copper conducts better than iridium.

Any thoughts on why the coppers miss and the iridiums don't?

Should I open up the gap on the coppers a bit more?

Should I just get Iridiums in a 7 heat range?

Measure the resistance of the Coppers to make sure that the resistance is not way off on one of the plugs(1,000 ohms). Also run you thumb nail on the insulation to make sure that there are no crackes or pitting causing a short which could happen under a load. Inspect the spark plug boot and make sure there are no signs of carbon tracking. A thin gray line inside of the boot which could become a path of least resistance.

I have see alot of BWM's run lean and start to burn small holes in the insulation. If you look at it with a 14x micro scope it looks like a small valcono of black soot is comming out of the insulation. To the eye it looks just like a defect in the insulation.

Hope that may be helpful