. I have one of those "colortune"kits that has a modified spark plug you screw in & it has a clear glass section down on the firing end & you can see the color of the flame! the sheet says you want a nice blue. trick as hell!
I have wondered if i could install a Colortune
and then aim my Harbor Freight video boroscope probe at the window of the Colortune,
and view the flame color while driving the vehicle.
I have heard that one challenge with the Colortune is squirming around to be able to get a good look at the window.
Spark plug choice wise,
the irridium tipped NGK's
set to the biggest gap your ignition can fire at redline rpm,
Are good value for the money,
and last a long time.