From the end on 2012 smart started also using FXU22HR8
F = Iridium
R = With resistor.
Obviously the electrode has to sit in the correct position in the combustion chamber.
The reach is the length of the 12mm thread mentioned previously.
The ceramic insulator is projected by 1.5mm and the spark position is 3.5mm.
Between where the power goes in and the spark comes out is a resistor (on the smart
OEM version), this controls the strength of the current to ensure optimal spark strength.
This is the gap between the centre electrodes and the surrounding earth electrodes.
Denso plugs come pre-gapped so you should not need to alter the spacing.
Performance Spark Plugs
They have taken their time but Denso have finally started shipping the Denso Iridium performance
sparkplugs to the UK. The part number is IXUH22. These are available from SmartMods.
If you have a preferred make of spark plug, simply match the information to that above.
Please remember that a lot of plugs claiming to be performance plug are anything but.
As is the case with the area of engines, there is a lot scientific rubbish out there.