Spark Plugs

Yes... a page just of plug info!

NGK makes miata's original equipment spark plugs.  Aside from the NGK plug installed at the factory, there are several different plugs that work and I've tried a few different ones in my miata.  Below is a chart of the different plugs I've used:

Stock Number Part Number Comments
2756 BKR6E-11 OEM plug
1283 BKR7E-11 One level cooler heat range than OEM plug
4291 ZFR6F-11 Extended reach, same heat range as OEM
2975 ZFR7F-11 Extended reach, one level cooler heat range than OEM

More details on deciphering NGK's part numbering methodology can be found here.

Flyin Miata sells the extended reach plugs, but I've also found them locally at Advance Autoparts.

I have reduced the gap from the factory spec of 0.044 inch to approx. 0.030 inch on each plug for boost applications.  Flyin Miata suggests this when running over 10psi of boost.  Too big of a gap, and the spark won't jump across the plug.  Too small a gap and the ignition for the air/fuel mixture isn't as strong (smaller spark).  The larger the gap, the greater the load on the ignition coils to produce a large enough voltage to jump a spark and discharge the coils.  There comes a point when the factory coils just aren't strong enough to deliver the required voltage.  Fortunately for most F/I miatas (say, running under 15psi), the factory coils can provide enough voltage to arc the spark plugs.  However, I've heard of some having trouble still with their coils.  Other ECU systems (such as Electromotive's TEC II and TEC III) utilize a separate coil pack better suited for the job.  I'm planning on trying a coil upgrade in the future that will work with the Link.

As for plug wires, I've used Magnecor 8.5mm competition wires and NGK "blues".  The Magnecors worked fine for a while, but I didn't really notice any difference in performance than the NGK blues.  The Magnecors are more expensive than the NGK's so I'm sticking with the NGK's from now on.  Avoid the black NGK wires; get the blue ones.

The OEM black NGK miata wires are notorious for failing.  Sputtering is often cured with new wires.