I personally would go for Mazda OEM spark plugs as our Owner’s Manual (strongly) suggested. Although the OEM plug looks the same as NGK’s but twice more expensive, I do remember some SkyActiv tuner (OrangeVirus Tuning?) says they’re different and it’s very important to use Mazda OEM plugs. I’d at least try NGK, not Denso.
Yeah I actually ordered Denso's, returned, then ordered aftermarket NGKs. Engine hasn't blown up yet
