swapped to all 9s form 7s/9s. Doesn't run real well on boost until it's really really warmed up. Is it the plugs? Cat maybe?

 

I would assume it would be longer warm up times, but no more than like a 5-10 second difference.

 

I don't think it is really a engine temp issue as much as a plug temp issue.

How much boost are you running? Where do you drive the car, on the street, auto-x, drag or road course?

The 9s will tend to foul easier than the 7s because the plug runs cooler (not the engine). Use 9s if you plan on running the car hard a lot under boost, not just driving hard on the street (7s are fine for that) but if your dragging it or running road courses.

 

My take on this is that plugs supposedly reach "self cleaning temperature", the optimum temperature for them to operate. Different temperature rated plugs have the core nose of the plug recessed certain distances under the face of the electrode depending on the design combustion chamber temperature. "Hotter" plugs have a deeper recess which makes a longer path for combustion heat on the plug electrode to dissipate to the rest of the spark plug and the engine head or rotor housing. Cooler plugs have shallower recesses so that hotter running conditions will not overheat the electrode to the point of it melting or setting off preignition or detonation. At least that is what some repair manual said (haynes probably).

 

thanks for the replies. i run 15 psi of boost. street only, but i do drive it hard. I never get into boost until the engine is around 80C or so by the pfc. It misses a lot even at 10psi. Later when the car is fully warm, around 90C I never have any issues.