I just removed my gas tank tonight and there is 4 fuel lines connected to a looks like a by pass valve mounted above the tank in the top of the trunk pan hump. this little valve bowl thingy has one fuel line exiting it.

Does anyone know what this is for?

Yep, that's the vapor separator. Each of the 4 hoses going to it should go to 4 corners of the tank. It is basically an emissions piece. and it does help to provide proper venting of the tank.

Without proper venting the tank will go to vacuum and you can get an air bubble in your fuel line which can stop you cold.

A 5th line should connect with the vapor return line from the motor.

Starting in 72' that line connects to the charcoal canister. The fuel tank vapor separator is part of evaporative recovery system and also acts as the fuel tank vent.

do ppl still use these or are there more modern systems available?

Like especially if youre taking your car to the strip, in that means is this set up sill applicable for racing?

I chose to restore my system to full functionality for my resto project. Most of these cars by now have had all of the under hood components yanked because they were considered "Emissions" related. Fact is, a properly maintained and functioning evaporative control system has no adverse effects for engine tuning/performance, unlike some other power robbing emissions hardware from the day. With that said, do you need it? no. The tank does need a vent, a lot of folks plug off the tank vents, run a vented gas cap and reportedly have no problems whatsoever.

Check your FSM. Fuel cap is "pressure-vacuum relief" type. cap is vented to allow air in but won't allow air out unless it reaches a certain pressure so essentially tanked is vented thru fuel cap if you choose to block off vent tubes.

Goofed when I first posted this. Cap is "vacuum-pressure release" NOT "pressure-vacuum relief". Sorry if this led to any confusion.

“Vacuum-relief” does not equate to “vented”. After 38+years what are chances the cap is original anyway? If you plug off the vapor collection/vent nipples, make sure the tank is truly vented somehow.

So is there reproduced charcoal ventilaters that I could buy?

Stant makes replacement OEM fuel cap for 1972 Charger, both early and late. Easy to tell that venting works, you just suck thru the vent hole. Also blow thru hole to test pressure relief. It should take extra pressure but not excessive pressure. Thats the way mine works and that is how the FSM says to check it.

I run a 73 gas tank in my 74. Since the venting systems were different I capped them off. I run a cheapie parts store plastic locking gas cap, vented. Works great. When I ran the stock cap, the fuel tank would create a vacuum inside, with the aftermarket cap it does not.