Yeah plumb back might be the way to go.
I've got a GFB Hybrid bov. U can plumb back full, half, or have full atmo.
It's just a matter of replacing the trumpet with the screw in plug.
I actually prefer the flutter sound it makes now rather than the loud pshhhhht blow off sound.
I think you only really get that if you are running a pod and maybe exhaust.
As for fuel economy, cant say yet, only plumbed back yesterday.
And yes, looks to me too like the nissan fuel gauge is not proportional.
On a crappier note, the f*cker that sold me my car claimed the timing belt and 100k service had been done.
After chasing him up for the receipt he promised he'd dig up, he finally spits out that it hadnt been done.
So i'm getting it looked at today, coz now I have now idea what it actually needs.
I've heard others say, when you get the car, change everything regardless. Sounds like good advice.
Hoping it's got old plugs. Coz if it does, that might explain fuel economy too.