Looking back through some old posts, I found the part # for the Denso iridium plug is IK22 (thanks Qadsan), but when cross referencing the HRC racing plug on sparkplugs.com, it referenced against the IK31 plug. Both have the exact same specs, but different part #'s. Are they the same, or which one should I run? Also, has anyone tried the IK01-31 or IK02-31 Racing plugs? They're quite a bit for a plug ($35 ). Thanks.