Trying to see what are a few mods I can do to my car to gain some more horsepower besides cold air intakes and plenum spacer

Intake, exhaust, cams, ECU tune... remove parasitic systems (ie Air Conditioning)... reduce rotating mass... reduce vehicle weight. There's more ideas out there, search, post, and utilize your membership.

Do you have a stick shift or paddle shift? New or used? Still making car payments (this would matter)?

Have fun and welcome to NICO Club!

Exhaust is one of the biggest improvements you can make for awesome results.

Same here. My mufflers were damaged before I got my '11. I can't find any specs on the sizes, etc. for the exhaust system. Do you have any idea of the inlet/outlet diameter of the resonators behind the cats? I have a cheap muffler shop nearby with an option of going full 3" cat-back (res delete) but in all honesty, the resonators do very little to restrict power and I believe Infiniti worked specifically to get a particular, unique sound when they developed the resonators. I don't need it to be louder in the cab anyway. I did however check out a few tech examples of 2.5" vs 3" pipes. The 3" pipes performed better than the 2.5", which I believe is the stock piping. The new mufflers I'm getting have 3" inlets/4" out. I'm in CA and to get a CARB official stamp on a set of headers is ridiculously higher than other states & not in my budget. PostalsQ - I have had headers on other cars and there is a noticeable improvement. How are they working out on your Q70? (That's the M version of the Q, correct?)

Again, I can't seem to find any specifics so any help would be greatly appreciated!

Thanks for all the tips and ideas!

I find conflicting data on OEM pipe diameters. I'd take a tape measure and get under the car and make a few of my own measurements if I were you. I did find that most measure at 2.375" with some claiming a smaller pipe right at the muffler. I'd look into 2.5" piping with smooth curves.