MBC, boost control question?

[Gamble97]

Ok, so I've got my motor built, in and running. Also have my new GT3561 turbo in. I did not yet hook up a boost controller. I have a MBC laying around that I'm going to be using. Currently the wastegate is running off the vacuum line from the turbo. It's a dejon turbo, so pics are on www.dejontool.com if anyone wants to look. Here's my question.
If the wastegate that I'm running (12-22lb spring) is running straight vacuum why am I at 12psi? Shouldn't I be at 22psi? For the mbc install, I would just cut this vacuum line and put the mbc inbetween?
Basically, I don't understand how adding the MBC works, if it isn't going to give me more air pressure, how I can run more boost. Or does the MBC leak air creating less pressure to the wastegate and hold it closed longer.
As you see, I know nothing about how boost works. Someone help me out.
Thanks

 

[SeeYaAWD]

...just cut this vacuum line and put the mbc inbetween?

Yes.

...does the MBC leak air creating less pressure to the wastegate and hold it closed longer.
Thanks

Exactly.

 

[brute]

The spring (depending on adjustment) is in different states of compression. If it isn't compressed at all, it's not going to require very much pressure to push the ball up. Think of the ball like a door. The spring is holding the door shut. So depending on how much pressure is already on the spring, the ball is going to need just a hair more than exactly that exact amount of pressure to be pushed the opposite way. Once the boost overcomes the spring pressure, it enters the chamber and goes to the wastegate actuator. Here's some drawings I just came up with. Hopefully they'll help describe better visually what I cannot describe in words.

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Depending on the type of boost controller you have, these specifics can differ. But basically the tighter the adjustment screw, the more boost needed to overcome it.

Tighter = You'll run more boost
Looser = You'll run stock boost

 

[spectr019]

As much as an F my teachers would give me from that diagram, that's probably honestly the most useful picture I've seen. You laid that out really nicely up there. Thanks for the sketch!!

Ben

 

[donmagicjuan]

I love brute's drawings. I give him a D-.

 

[brute]

Don, a D- is passing, that's all I care about

I drew that up specifically for this thread, and as I was posting it, I figured it was pretty useful info, so I went ahead and added it to my Tech Article on How To Install A MBC. Paint is super easy for me to use, but sometimes my OCD kicks in and I start spending like 30 mins per drawing. Then I stop, , , , then continue on. I'm glad they are useful to some people. I'll try to keep the "quality" coming