Quad electrode: I measure the distance between the electrode and the tip of the prong. It is always more than 0.042". In theory, the quad sounds great, in reality, spark can only jump to one prong. IMHO, 0.042" is too much of a gap.

I learned the Iridium lesson from my 2007 Honda Odyssey van, which came from factory with NGK Iridium. At 65K, it looks like new, gap was still within spec. I was sold.

Then I started doing research for my E39, put NGK Iridium (gap 0.028") a few years ago, engine smooth like silk, no hiccups.

Ditto for my X5, smooth, fuel mileage is better than the quad thingy that I threw away.

The best bang for the bucks is, IMHO, NGK Iridium $7/each. Better than BMW dealer pricing!

The larger gap is not an issue.

As I mentioned in my inital post, 2 & 4 prong plugs spark across the insulator surface, there's lower resistance because of surface ion alignment prior to spark.

At any given voltage a spark can jump around TWICE as far across a surface then an air gap.

FWIW, I pulled the OE 4 prong plugs at 105k miles and they looked good, 4 spark paths visible on insulator surface of all plugs.

what are You running in your 4.8is?

Good question:)I will let you know once I take the original ones out next week lol
What I know is that I'm going with the NGK iridium

I am going with the NGK also, I just installed OEM,they run Okay but ,Mike Aya and others with the 4.8IS say very good things about the NGK IR IX.............and better MPG.

No complaints with NGK plugs here boys