If I’m going to upgrade the throttle body on my 06 G35x to 75mm, is it recommend or necessary to install a plenum spacer?

 

You should do the plenum spacer simply because it's the single biggest bang for your buck performance mod. The throttle body upgrade alone will do VERY VERY little, you need a 3.5" intake along with that throttle body otherwise there wouldn't be enough airflow through the tube to even supply the throttle body. Keep in mind that the 3.5" intake will require an uprev tune as well.

 

I read yesterday that the plenum spacer does not do much for the 05-06 g35. Trying to see if that’s true.

 

Only if you have the rev up engine, most 2005-2006 we're still using the regular DE engine. Only the 6mt equipped ones came with the rev up.

Your X chassis was only available with the 5AT so no revup option.

The rev up doesn't benefit from the spacer alone, it also needs the MREV2 lower plenum which is a modified regular DE lower plenum.

The rev up with spacer and MREV2 is the biggest N/A HP gain.

The regular DE with a plenum spacer is the biggest N/A HP gain.

 

Thank you.