Hi all, I'm trying to work out the last few bugs on my twincharged system (see 3rd gen section if you're interested). I'm trying to figure out how to bypass the supercharger when the throttle body is closed.

I was thinking a dual port wastegate, with the side port (boost reference) connected to the supercharger side of the throttle body. And the top port (vacuum reference) tied to the manifold side of the throttle body.

That way, any time there is a pressure differential between the sides of the throttle body, the wastegate will open and allow air to vent or enter.

The part I'm having trouble figuring out is the spring size in the wastegate. I understand how a wastegate works, but don't understand one item.

The wastegate will not open if there isn't a line hooked up to the manifold (to push the diaphram open), no matter what size the spring is. I think I'll need a very light spring to make what I mentioned above work.

If I just remove the spring entirely, will the wastegate open any time there is the slightest difference in pressure between the two ports? Or will it just flop open whenever it wants.

Since it doesn't matter which spring size is in there when no pressure source is hooked up (wastegate stays closed), would it still stay closed without a spring at all and no ports hooked up? That is the part I don't quite have a handle on.

 

An external wastegate can be forced open if there is insufficient spring pressure. The force working on the poppet valve at the bottom will push it open.

 

I would think a standard BOV would work -

It operates on pressure differentials. When the throttle body is closed (VAC) and there is positive pressure (SC side) the vac will pull open the bov while the pressure will also push it open.

under equilibrium the light spring will hold the valve shut (boost with throttle open in your case).

The principle should work on syncronous (idle) operations just like transients (throttle snaps) on your case.