I've been abusing my car again, in ways that would make most take a big step back!
Having established that I could keep the waste gate close all the time and produce over 30psi, I was left pondering a way to control the boost to stop the ECU fitting.
It came to me while I was in one of those half consious moment, while I was deep in though trying to get to sleep.
I rigged up the same pieces as before but in the order shown below. I'll start by explaining how the standard setup works for those who don't know.
The turbo waste gate diverts exhaust gasses around the turbo turbine, in order to reduce it's speed and thus reduce the boost pressure it produces. The waste gate on the 1.9CDTI is normally open which mean the gasses bypass the turbine and the turbo doesn't spin up. This must be for safety, if it goes into limp home mode for example. There is a vacuum line from the engine to the waste gate that the ECU controls, so that it can close/open the waste gate to control boost. Still there?
Right, now what I did was to grab a DC vacuum pump, a 'T' piece, a mechanical bleed valve (boost controller from Halfords) and some pipe. I then connected the vacuum pump to the waste gate through the 'T' piece to hold the gate closed all the time (all the gass flowing over the turbine for max pressure). The third leg of the 'T' piece was connected to the normal vacuum line via a variable restrictor (my modified boost controller). The normal vacuum line varries the vacuum as I said, so without the restrictor the system would act pretty much as normal with the vaccum being released by the ECU controlled line. Because of the restrictor though, my vacuum pump holds the waste gate closed more than the ECU would and as such I get a crude adjustment to the level while leaving the ECU more or less in control.
The result is that boost now peaks at upto 28psi on over boost (as apposed to 24psi) and holds at 24-26psi (as apposed to 22psi).
Don't know what the bhp/lbft result is as yet but hope to get some figures next weekend or the weekend after. Doesn't suffer from increased lag and I've abused it in sixth upto ... well more than one should and it didn't complain.