Boost control

[axaQ42]

No the pipe is brand new also we blocked that pipe for testing and the boost went skyhigh...so that proved that there is no boost leak.I have taken it apart and as it supposed to be ...evertyhing was nice and clean and ok.For me the only logical expalantion is the spring which is too weak.We are going to try to change it for a stronger one or just stratch this one for a a few mm.

[axaQ42]

Problem solved...as we thought the original MBC spring needed a nice stratch and a few "rings" cut off to get the right setting for the controller .

[#84]

Many interesting devices! The relief valve principle is really brilliant, so that no pressure at all reaches the wastegate actuator below a certain boost pressure.
However, I am very sceptic to all these devices which have as purpose to maintain the boost pressure even at higher engine speeds. A closed loop control would be fantastic, but as I understand it all these aftermarket electronic boost conrolers are excellent at keeping the boost at a certain level, but they have no functionality to adjsut boost v.s. speed. With the Q4 as an example; it boosts about 1,1-1,2 bar in the midrange with standard chip+turbo. If that boost could be held up to 6500 rpm, there would be no chance to supply it with enough fuel...

Anyway, I can see a few other strategies to a) have better boost build up b) have better boost control:

* Do not run the Pierburg Valve at primary boost build up - you will just re-circulate air through the PV to the compressor inlet.

* Use a two-way waste-gaste acuator. Put pressure on the closing side to help keeping the waste-gate closed during boost build up and on the opening side when controling boost at higher speeds. They do excist, but where do I find them?

* Use so called air injectors with inverted logic instead of Pierburg Valve.

* Run closed loop boost control within the ECU - RP-lab offers it now and I will order it soon

[Evodelta]

QU: "With the Q4 as an example; it boosts about 1,1-1,2 bar in the midrange with standard chip+turbo."

Is it really as high as that??

Your theory about the injectors not being able to produce enough fuel at higher rpm/higher boost is ok, but in practice most aftermarket chips overfuel anyhow, so the increased boost may even things out a bit - only an AFR test will tell the truth.

One-size-fits-all chips are crap anyhow, no two engines or conditions are alike, mappable ECUs are the only way to get it right.

[jimnielsen]

I have found that you can keep the AFR at about 12:1 with boost @ 1.1bar to 7000 rpm using the standard injectors, turbo, ecu. Properly mappable ECU's like autronic/motec - where you are not left to guess/experiment with the table values - would make it simpler.

[#84]

Evodelta:1.1-1.2 bar is with modified air filter and exhaust system, but that is pretty normal upgrades.

Jim: The exhaust back-pressure will be very high at 7000 rpm and 1.1 bar, so it is reasonable that there will be fuel enough. However, my point is that it is around this boost pressure you find the upper limit at top speed, but if you tune your engine you probably want to raise the boost pressure in the midrange and then a flat boost curve is not very suitable.

/A