Which plugs are best for performance?
I took a more scientific approach to this question a few years back. I compared the primary resistance in ohms of new 4 each AC, Champion, Autolite, and NGKs all same application for a 340. Resistance values will give you an idea of the consistency and spark energy going to the cylinders. Champions were the highest resistance, AC next, then autolite finally NGK. Champions varied all over the place between 10 Kohm up to 20 Kohms. AC were lower on average but still in the 10 +Kohm range, autolites were between 5 and 10 Kohm. NGKs were consistently very close to 5Kohms +/- 500 ohms. Guess which plugs I recommend ?