Am I right in thinking 0.7bar at the wastegate actuator should open the wastegate? I want to check it's OK because I'm having problems with overboost with the standard 2-port solenoid and also with a Dawes MBC when I tried that (car is MY00 with boost target 20psi). Fuel cut heaven occurs in 4th or 5th if I floor the throttle from low speed. The boost builds and reaches 23-24psi and stays there until the inevitable happens. If I floor it at higher revs with the turbo already spinning some then the boost control is much better but hardly confidence inspiring.
I'm thinking a simple test would involve running a pipe from the turbo nipple to the actuator, connecting a boost gauge to the manifold, and looking for a max boost of 0.7bar when driving. If I use a regulated independent air supply, is there a specification regarding when the actuator arm begins to move and how far it should move as I increase the pressure?
Kevin

 

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You say that target boost is 20psi; what dictates this?

Boost generated will increase with engine load therefore the higher the gear the higher the pressure. If you're setting up the boost control system to achieve target boost in say 3rd gear it will overshoot in 5th, unless the boost controlling device has compensation functions for gear such as some Subaru ECU's and the Apexi AVCR.

 

Does this mean an MBC will always be a bit rubbish because it needs to be set up to give its maximum boost in 5th and therefore you have to accept that in lower gears the car will then run lower boost than it could do to prevent overboosting in 5th? And why such a massive (3-4psi) difference in held boost between flooring from low revs or after revving out in the previous gear?
My original problem was that not long after having the car EcuTek mapped I found it would sometimes cut out (fuel cut?) briefly, usually if flooring the throttle from low revs in 3rd gear, the cut-out usually occurring around 6000+ revs (strange really, as boost is tailing off at this point anyway).
I connected a boost gauge and found in 3rd boost peak at 21.5psi and settled at 18.5psi before tailing off to 15psi at the redline. In 4th peak was 20.5psi, settling at 19.5psi before tailing off to 14psi at the redline. I didn't try in 5th because the other half scares easily.
I figured I would try an MBC as I thought I could go for a stable 20psi tailing off to the redline, so might even gain a bit of performance but get rid of the cut-out.
But as I said in my first post I just couldn't get the boost stable. I've since tested the wastegate - it starts to open at 9psi, is half open at 13psi and is fully open (rod moves out about 12mm) at 20psi and doesn't lose pressure so I assume it's fine.
The strange thing is since reconnecting the boost solenoid, the original problem is worse than before. It now hits 23psi peak in 3rd with that. The solenoid isn't very old but I'll clean it in case it's sticking to see if I get back to how it was in the beginning.
Can I expect better from the MBC or am I going to end up putting a bigger restrictor in the pipe from the turbo nipple to reduce boost?
Kevin