What is this vacuum tank for?

[wtfisafleek]

It's apparently part of the airbox system, or at least it's on that parts page.

[Fleetw00d]

That tank and solenoid are to operate the intake bypass valve (#18). At engine speeds below 3500 rpm, valve 18 is closed and intake air only goes through pipe #13. Above those speeds, the valve opens and air is taken in through both #13 and #22 and #16. Just downstream of the valve is a connection to the resonator chamber that is supposed to reduce intake noise. If I remember correctly, the valve has to be powered (by vacuum) closed, so if you disconnect the electrical connector, the valve will remain open all the time for less restrictive feeding of air to the filter.

[wtfisafleek]

Ok I see now. I had my ideas, but the way #49 just stops, I wasn't sure. I'm guessing vacuum hose #49 leads to #33 (check valve?) and onto the small vacuum tank #38.

[Fleetw00d]

#49 goes on a nipple on #39 or #38 (it mounts on the fender wall just above the valve). #33 is way back where the vacuum comes off the plenum. Some models use just #17, eliminating the valve and secondary feed pipe. #17 just goes to the lower connection to the resonator chamber and the engine breathes only through the upper pipe.