I just installed NGK Iridium, heat range 8 (bpr8eix) & immediately I experienced hesitation at high rpm & boost (20-21psi) Never had such issue with the previous set of plugs which was heat range 7! I reinstalled the 7s & that eliminated the hesitation.
A friend is suggesting that the new plugs might require gaping (decreasing gap from 0.8mm to 0.6mm) But I heard that Iridium plugs are not suppose to be gaped!

Any suggestion what the problem might be?

 

what mods have you installed that warrant an 8 heat range plug?

 

i have the 8's iridiums and i regapped them to 22 and it works fine.

 

Did you have any issue before regapping the spark plugs?

 

i always gap spark plugs to what i want. i think they come like 28-30 or so out of the box.