I am about to install a few mods which is a k&m air filter and plenum spacer. I am thinking that my air to fuel ratio is going to change with these two mods. Will I need to get the ECU remapped or will it auto compensate. I am running a stock 350z GT4 rev up engine

 

AFR isn't going to change, but you'll suck a lot more dirt and grit into the engine with a sh!tty K&N filter. Maybe hotter air, too, depending on which one you install.

 

What do you recommend for the intake other than FI

 

Nothing wrong with the original airbox and filter on that car. Use an OEM Nissan filter or a Purolator.

 

^This.

- Another FYI for the future.. Do not use ANY oil-based air filters with these motors. They are not needed, and the petroleum will eventually start to break down the scrubbing-sensors within your MAF sensor. The pleated paper(OEM style) air filters are all you need for N/A.

 

It doesn't matter how many modifications you put on the car, the ECU will do the compensation which is why we have to get it remapped to see any benefits.
You might as well do the exhaust too before remapping if you're staying NA with basic bolt on parts.