Owners manual calls for 100K mi service interval for the iridium plugs, but I do drive quite aggressively. Just noticed over the past few thousand miles that the car doesn't quite feel as sprightly as it used to and I'm not sure what else to look at.

 

FSM calls for 100k and that's when I did it. The plugs still looked alright when I pulled them out and I didn't notice any difference after anyways. Your problem might be something else.

 

Agreed^^ No matter how hard you've pushed your G, unless you've done significant engine modifications it's unlikely the NGKs are the cause. Why not spend some money getting your car on a dyno and getting some baseline figures? That way your butt dyno will never be fooled again, or you can establish some problems.

 

did a few 3rd gear pulls with the torque app on and logged some knock events between 2000-4000rpm. Any clues?

 

Are you using premium gas? And if you're in CA maybe it's because of 91/E15 blend..

 

Try cleaning your throttle bodies. That has been a recurring issue for me once response starts waning.

 

I changed mine around 105k miles and they were not bad

 

93 octane e10. Top tier. Not the gas. Anyone think it could be false knock from something like a loose heat shield?

 

did that about 20-25kmi ago. Time again?

 

Changed mine at 82k on a xS Sedan, to GTR Plugs as recommended by R/T. I don't notice a difference tbh.

 

Sebastian@Specialty-Z told me to change plugs 15-20k miles. He see combustion leak by that time....

 

Spark plugs every 15-20K sounds like a waste.

 

Yeah, total waste of money.

 

Waste if OEM, but if your running copper's that's about right. Although I don't see as much love for copper here as I did in the Maxima forums.

 

Replaced mine at 100k....no difference in performance or gas mileage.