Adding both will raise the A/F slightly, but it doesn't necessarily mean it will be lean.

If you are boarding on lean before the install, then yes, it would push it into lean.

If your A/F is rich to normal before you add it, A/F will be good after installation.

 

So by adding just the spacer & not the mrev2, i will not run lean .. only if I do both right? I think I am just going to do the spacer.

 

there are other variables to consider... I had Stillen hi flow intake and cat back exhaust, a/f was fine… added MD ½” spacer, a/f was still relatively okay … added HFC, a/f went to **** and was running quite lean, got a re-tune, added some fuel to get the a/f in spec =

Some people have leaned out after just a few breather mods… the only way to know is to dyno with a/f

if all you have is spacer - it's doubful you will be lean

 

So Dyno is the only way to know if you are running lean or not. I don't even know where a Dyno is near me! (Louisville, KY)