legacycentral bbs

Has anyone actualy done a MBC or bleeder valve after the stock boost conlroller? I've heard not to but I saw on the rsliberty site that the boost controller is not open loop. So it just pulses at a steady predetermined rate. That would explain why I get 10psi with the stock boost controller, my exhaust and turbo. I'm thinking a MBC won't work well but a bleeder should.

You mean the stock control is open loop...

It isn't closed loop but it isn't completely static either, from what I understand... it does vary the duty cycle based on some of the sensors and stuff. For example, it will try to give you more boost if barometric pressure is low. But it doesn't have a closed feedback loop with a desired value.

What advantage do you expect to gain by using an MBC in conjunction with the stock boost controller? I agree with you that a bleed after the stock solenoid would get you increased boost, but it's a little weird to have two bleeds in series. Why not just replace the whole thing with a ball-and-spring valve?

No real reason, I just remember somebody say you couldn't.
Could you say, make an adjustment to the duty cycle.... ???

You can, but it just kind of throws the dynamics out of whack since you have a less predictable nonlinear device in the middle of it.

You may be able to trick the ECU into changing the duty cycle by, for example, convincing it you're up in the mountains rather than down at sea level; I don't know. It would be interesting to try.

It would probably be simpler to make a replacement controller for the solenoid.

Note that the stock boost control does not have a fixed duty cycle. It varies the duty cycle with throttle position (and perhaps something else) from around 0% to around 50% (very roughly).

Huh. I wonder if one could make a simple inline boost controller that would simply increase the duty cycle using a little one-shot triggered by the rising edge of the ECU's output line. That kind of controller might even work without having to cut any wires (it could just tap into the ECU's boost control solenoid wire). It could just lengthen each pulse by a fixed amount, increasing the pressure bled off. One of these days I'll try to come up with one of these. In a sense it would be like a tiny turbo timer.

I get so many ideas while writing posts on this BBS. I love this place. If only I had time to try them all out.

I had mine setup exactly like that -K- turbosmart type one bleed valve and the standard boost solenoid, with a one way valve on the map sensor to eliminate boost cut, very dangerous to the motor. I was running a maximum boost spike to 20psi and settling back to 17psi by redline, the funny thing is now i run a bleed valve on the map sensor and a bleed valve from the turbo compressor outlet to the wastegate line and its running 15psi max spike settling to 13psi by redline and its going faster than before, because it is running the standard fuel map (just a little bit leaner) because of the bleed valve on the map sensor, and with the bleed valve on the map sensor you can successfully trick the computer into thinking it is running 14psi when it is actually running 16psi.I have raised the std fuel cut of 14.7psi to 17.5psi just by using a bleed valve on the map sensor.