Dual Port Manual Boost Controllers
 

Functionally speaking, what is the difference between these two different styles of plumbing a dual port / tee style manual boost controller (MBC)?
http://lh4.ggpht.com/__pqkhEfdq8I/Sz...mbcinstall.jpg http://lh5.ggpht.com/__pqkhEfdq8I/Sz...400/schjv4.jpg

Not sure i get your 2nd drawing, why are 3 lines hooked up? The black knob style controller that BoostSciences has does have 4 ports, but only 2 are hooked up. Never seen it the way you have it plumbed in that picture.

I guess technically a ball and spring type controller could be a 3 port, but the 3rd port vents to atmosphere to prevent boost spikes. But you wouldnt use a ball and spring type with a dual port wastegate.

The BoostSciences drawing was taken directly from their website.

The theory behind the second drawing is that the bleed-style (as they are known) exerts pressure on the wastegate spring, keeping it closed until a threshold is reached, thereby preventing boost creep AND spikes simultaneously...just trying to determine if the first drawing effectively does the same thing.

FWIW, the BoostSciences MBC looks identical to the one that Lindsey Racing sells, and L-R have the same drawing on their website for plumbing with a dual port wastegate.

Also, to be clear, my application is on a 931, which as has the 930-style dual-port wastegate. Meant to mention that at the outset...

What type of controller are you using for the 2nd picture?

I am familiar with the 1st picture and have that style controller hooked up with a Tial dual port. It does the same thing, which is send the air signal to both sides of the diaphragm helping keep it shut as you build boost. Whether it does both prevent boost creep and spikes i do not know. I have just never seen a 3 port boost controller hookup like in the 2nd picture.

A fellow 931 owner is using the second type on his car. It's made by Forge, and they refer to it as a "bleed" style controller:
http://lh6.ggpht.com/__pqkhEfdq8I/Sz...0/FMICB051.jpg

Also, it apparently does not use a ball and spring, but rather a conical fitting on the end of the screw. The guy who is using this claims that the response is much smoother, less harsh than the ball and spring style.

I just looked at your thread on RL and saw you are refering to a Forge controller. If you look at the fitting instructions on the Forge main site it says that the bottom port is meant to vent to atmosphere.

"The bleed port on the manual boost controller is just to be left open bleeding into the
atmosphere. This reference is not to be connected to any other part of the engine."

Here is the link.

http://www.forgemotorsport.com/content.asp?inc=product&cat=0029&product=FMICB051

Right, I know, but the fellow I mentioned has the bleed port connected to the top of the wastegate ;-)