Going to get my spark plug TSB performed next week. Should I upgrade my spark plugs and have them replace them while they are at it? If so, will I see HP gains if I buy a better plug?

 

My car feels peppier with the TSB plugs in. Probably Placebo effect.

I don't know if the Denso Iridiums did anything. Someone told me they need to be changed frequently for best performance. Don't know if anyone can substantiate?

 

New plugs, no matter what kind, will make the car seem a bit peppier for a while. That said, I still think the Denso iridiums make a difference, especially when gapped fairly aggressively (40-45 mils). They do need more frequent replacement than platinum plugs, though.