I've heard through various sources that this is the plug to use in spec Miata racing because the longer threaded section takes up some of the combustion chamber giving a small bump in compression and therefore power.
Does anyone have any first hand experience with this?
No first hand experience but looking at the specs of the two I can't imagine that tiny bump in compression (probably under 1% difference, the difference is just in the tip projection) will make any measurable power increase.
A longer projected tip can give a better burn though, as it lights it off closer to the center of the chamber. That also has a similar effect to slightly advancing the timing.
Do you "clock" the spark plugs too? (clock means to buy 20 or more spark plugs and screw and unscrew until you find the 4 that keep the 'tang' (cathode?) in the optimal orientation for combustion).
In reply to Robbie:
They make washer/shim kits to degree the plugs too
I went to do it on my KA24E build when I had the head off and found that factory plugs with the correct torque were near perfect clocking.
We've been selling the ZFR6F-11 for a couple of decades 
We figure the extended tip gives a better burn by starting it closer to the center of the combustion chamber.
I don't believe we have ever burned through a couple of hundred bucks worth of dyno testing to verify a $12.95 set of plugs, though.
Keith Tanner wrote: I don't believe we have ever burned through a couple of hundred bucks worth of dyno testing to verify a $12.95 set of plugs, though.
I bet McLaren has. Of course, their spark plugs probably cost a lot more than $12.95 a set, too... :)
codrus wrote:Keith Tanner wrote: I don't believe we have ever burned through a couple of hundred bucks worth of dyno testing to verify a $12.95 set of plugs, though.I bet McLaren has. Of course, their spark plugs probably cost a lot more than $12.95 a set, too... :)
Back when I had my dyno I had several customers test out: wires (3 vendors), plugs (several vendors), fuels, oils, hub grease(!), etc
I recall there were some $25 / ea spark plugs that made some decent gains (> 2HP).
Kendall
We did test some of the magic plugs years ago and determined that they didn't work any better than the NGKs
When Miata owners start paying McLaren prices, we'll start providing a dyno chart with every single set of plugs we sell.
https://www.flyinmiata.com/ngk-extended-reach-spark-plugs.html 
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