Manual Boost Controller

[rich850t5]

OK so i have a boost gauge set up to monitor mbc settings,i have it currently set at 13psi however i can turn up the boost to 21/22psi and as long as i stay in sport mode it wont cut the timing but if i use econ mode it will cut back at 15psi QUESTION 1:WHY IS THIS?when it reaches 15psi it just picks up the front end points it at the sky and screams off up the road as if ive hit the nitro button boost goes up to 21 then drops back to 15 and holds this through the rest off the gears(auto)QUESTION 2 AGAIN WHY IS THIS? a confused t5 owner!oh and QUESTION 3 WHAT IS GOING TO HAPPEN IF I KEEP LETTING THE TIMING CUT BACK(IE DAMAGE TO ENGINE)?

[CAMO]

Just changed my bleed valve for a MBC- a great deal better+ now running nearly 1.0 bar boost on standard chip!

[dj_rog]

OK so i have a boost gauge set up to monitor mbc settings,i have it currently set at 13psi however i can turn up the boost to 21/22psi and as long as i stay in sport mode it wont cut the timing but if i use econ mode it will cut back at 15psi QUESTION 1:WHY IS THIS?when it reaches 15psi it just picks up the front end points it at the sky and screams off up the road as if ive hit the nitro button boost goes up to 21 then drops back to 15 and holds this through the rest off the gears(auto)QUESTION 2 AGAIN WHY IS THIS? a confused t5 owner!oh and QUESTION 3 WHAT IS GOING TO HAPPEN IF I KEEP LETTING THE TIMING CUT BACK(IE DAMAGE TO ENGINE)?

The ignition timing does not effect the boost level at all. The boost levels should be the same for both sport and econ mode if you have a MBC fitted (and even if you don't I think).

21 psi sounds rather too high to have set the MBC - but I am not sure that this is the pressure you have set it at. I think you are getting serious pressure spikes which are taking you up to 21 psi. This is because you have tightened the waste gate actuator. You don't need to tighten the WGA if you have got a MBC installed. The reasons for tightening the WGA are to keep the WG shut for longer when the boost is building. As you have a MBC installed, waste gate creep will not occur as the WGA will not "see" any pressure until the MBC pops open. Running with a tighter WGA will just give you potentially dangerous spikes. Put it back to standard!


Hope this helps and you haven't trashed your engine already...

[dj_rog]

Matt, when i was thinking about an MBC, there was a lot of confusion from various people about MBC's being different from bleed valves and so on. I have come to the conclusion that the two things work in exactly the same way. My valve has two ports, but has a hole in the valve body for air to bleed from. The valves with three ports are just the same, but i beleive can be fitted in the car, so they can be adjusted while driving. the 3rd port in this case has a tube fitted to it which terminates with an open end anywhere in the engine bay. I would imagine that this particular valve could be fitted in-car or under the bonnet.

I replied to a similar sort of question in another thread.
I bought a MBC (2 ports) off ebay and fitted it to my car. I could not adjust it to give me low enough boost levels. I took it out and had a look at it and noticed it had a hole on the body of the MBC. I worked out what was happening - when the ball baring in the controller was lifting to moderate the pressure on the high pressure side, air was bleeding out though this hole causing a low pressure in the line to the WGA which closed the WG which caused the turbo to generate a higher pressure than I wanted.

I blocked the hole on the body of the MBC and found that I could then adjust the MBC to give me the pressure I wanted (about 0.9 barg).

So, if you buy a MBC and it has a hole on the body, block it up!

any questions - please ask me...

R