Firewall vacuum connection
 

I’m trying to figure out what this hose goes to. It’s centerline just behind the manifold and under the front strut bar studs. Sorry for the terrible pictures.

Looks like brake booster. Is it on the drivers side of the car?

It’s dead center of the car

It could be for the brakes, but, usually the vacuum line would take the shortest path from the intake manifold to brake booster housing unless Nissan decided to route it behind the bulkhead.

I don't think there is anything under the dash that is vacuum operated.

Check the work shop manual to see the diagram.

I keep forgetting to look for it on my car. I was working on it this afternoon. Too late now.

OP, take the cowling off and I imagine you can see what the vacuum line goes too.

It goes to the brake booster

Okay, everyone was right… it was for the brake booster. Is anyone running the Motordyne M370 manifold? The directions say that connection is where the PCV connects.

nah the pcvs are in the valve covers in front and go to the two front ports

Edit: you have an hr manifold that only has no "pcv" barbs, so you are going to have to y connect them and run that to a t on the brake booster barb.