It's running smoother? I know that's subjective. What's the gap variance between the two plugs? You'll probably need to put a little load on the engine and really get your sensor warm to look at A/F. I wouldn't think that ignition would create change in o2 though. FWIW, sneak up on boost until you decide that you are running a cold enough plug for the application. I'd also pull a plug and look at the strap coloration to get an idea where the timing should be. You may need to use a fresh plug and do some running/cutting the engine to look at your plugs. Here's a site to ponder: http://www.4secondsflat.com/Spark_plug_reading.html

BTW, how much boost are you running?

 

Actually, it's running a lot worse. But the AFR's are leaner, we're trying to diagnose what's going on in my thread on the topic ( https://www.miataturbo.net/showthrea...575#post869575 )

The weird thing is that under heavy throttle, the new plugs run the best the car has ever ran in the time I've had it. But anywhere else, it's not so great. Gap is set to approximately 0.30 (As measured by a wire gapper), same as the old plugs.

15psi. I'll be increasing it to 18psi one of these days, though. If nothing else, to only say I run 18psi.

 

That's not yours, is it? Shoulda bought the Mann filter from Amazon. They provide BMW OEM.