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cant turn down boost?

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djj624

Member
Joined
Jan 8, 2008
Messages
656
Whats up guys. Im having an issue with my MBC i have it turned up to 20psi and i cannot get it to go any lower? When i installed it i loosened the wastegate rod till it was nice and easy to pull over. Installed the mbc as you would an rjc unit only added a hose going in the car. Whats going on here? Ill take a picture being im going to my warehouse to take some snapshots of a gas rc car im selling.
 
Is your boost controller an RJC? I believe there's a number it can't be turned any lower to go.
 
Im thinking this might be because of the the main controller mounted in the engine bay next to the throttle body?

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It depends on the turbo and wastegate setup... hole size in the wastegate.... puck size.... which turbine housing..... and exhaust wheel design.... I have a friend with a 74GTQ that makes near 20 psi with the wastegate arm unhooked completely from the actuator....

I inquired about that to someone who should know... and he said it has happened to him before as well.....

I would have never guessed you could build any significant boost with the puck completely open.....but you can in certain cases...
 
Get rid of the restricter tee and run the hose that's going into that directly to the gate. Don't use any part of the factory control system.

EDIT: if you want to be able to control the boost from inside the car tee the bleeder into the hose that runs from the compressor to the controller. Here's a pic...try not to laugh. :D
 

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Nice pic (holding back) hahahahaha!!! just kidding i couldnt resist. Anyway which T are you talking about the metal mbc underhood or are you confusing it for the y that is connecting all the vac hoses? Im wondering why there are 2 mb controllers one in and one out.
 
If you're talking about my awesome picture then the square I have labled MBC only has one input (compressor side) and one output (gate side). The other line on the gate side is just part of the arrow I drew pointing to it. The verbal of how it should be set up is as follows.

One vacuum line going from the compressor to the mbc (line 1). Then one line going from the mbc to the gate (line 2). If you want to be able to change the boost from inside the car you can tee a bleeder valve into the line going from the compressor to the mbc (line one). If you do that you can set your minimum boost with the mbc and then use the bleeder to raise it above that point.

Edit: DO NOT use any part of the factory boost control system. DO NOT use the factory restrictor tee for anything.
 
One vacuum line going from the compressor to the mbc (line 1). Then one line going from the mbc to the gate (line 2). If you want to be able to change the boost from inside the car you can tee a bleeder valve into the line going from the compressor to the mbc (line one). If you do that you can set your minimum boost with the mbc and then use the bleeder to raise it above that point.
Isnt this the way i have it now?
DO NOT use any part of the factory boost control system. DO NOT use the factory restrictor tee for anything.
Im using the factory y/t to run the bleeder into the car? How would i get rid of it and still use the bleeder:confused:
 
I think i know what you mean now if so dont hesitate to call me SLOW!!

I now have the Y for the bleeder tapped in from the gate side and not the compressor side. Is this correct? Your saying to run a line from the underhood mbc to the compressor and T the bleeder into that? Then run the other side of the mbc directly to the gate?
 
Yes, that is EXACTLY what I mean. :smile: Also, if you're going to use the restrictor 'Y' then I would make sure the restricted port is going to your bleeder.
 
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