I have a Hallman MBC and a HKS WG.
(after searching)
I've read some different ways to hook up the MBC to external WG's.

one being, leave the top nipple on the WG open and put the boost controller output to the bottom nipple. Instead of manifold pressure opening the WG, a differential pressure opens it. Example, Manifold pressure is 1bar, and the WG sees .6bar (which the spring is rated) and boost is limited to 1bar.

PRO: 1 less vaccum line.
CON: ???

The way I have it set-up is manifold pressure on the bottom nipple (if top nipple left open, boost is limited to the spring rate) then the output of the MBC to the top. Now, the thing is...if the boost controller is SHUT, boost is limited to the spring rate (or slightly higher, since a small amount of pressure will fill the chamber with the spring). Opening the MBC allows a differential pressure into the top of the WG. In a way increasing the spring rate, air pressure + spring rate is now what limits boost. <-- anyone see a hole in this story??? IF the MBC is WIDE open, the WG will never open. i.e. Spring Rate + MP > MP

I assume there are two nipples on a wastegate for a reason. I'd like to think, that the added air pressure to the spring keeps the WG shut "longer/better" to get faster spool.

I'd like to hear some thoughts, before I start rerouting vac lines and running tests to find out it makes a 1/2psi - 250rpm difference

Someone entertain me.

TIA.



for some reason, I like the idea of a ball, 2 springs, and a diaphragm keeping my motor under control so it doesn't self destruct YOU CAN ONLY HOPE TO CONTAIN IT

 

Run the output from the MBC to the bottom nipple on the wastegate and leave the top nipple alone. This is how I connected on my friends 400HP T2 that had the standard 40mm HKS wastegate and a manual boost controller (ball and spring that I made using the Grainger pressure reilef valve). If you were using an electronic BC then that's a another story as differential pressure and the solenoid valve is in the equation. The MBC is much simpler to connect and use but you may have a short boost spike then it will settle down. Just make sure that the output hose from the MBC to the lower nipple on wastegate is kept short as possible.