with just the black maxx I am only pushing like 29 psi of boost with the fleece i am pushing 32-33, that is still in the map of the turbo. You can close it all the way and the turbo spool is faster, or you can close it and its alittle laggy and smokes alot like a smoke switch, this is while taking off, while cruising you can close it and the boost will go up to about 7-8 psi and the egts will drop a couple hundred degrees on my truck, or you can open it up for fuel milage. If you starting to lug alittle going up hill and ita almost ready to downshift you can close it and it will spool you up and pick up power. Running with it closed on top end it will clear all my smoke away, or likewise with it open it will dump alot of smoke, I just barely started playing with it alot, so learning more things with it. I might be backwards on my open and closed though, but I think I got them all right.