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Since I just put the final touches on my new programmable electronic boost control setup I felt like canvasing you lot to see who's doing what for aftermarket boost control.

I initially played with fitting a bleed valve on the wastegate line after the boost control solenoid which kept the factory boost curve but lifted it slightly, but wasn't satisfied with the level of control, so I went and bought a solder-it-yourself kit from Australia (my home country) for AU$150 which is working very nicely. I've got it set up for about 12psi with absolutely zero wastegate creep. This kit's a bit unique in that rather than bleeding air away from the wastegate actuator line like the factory system, this is re-plumbed so that no air can pass the control solenoid into the wastegate line at all unless you pulse it. The kit takes injector duty cycle as input, spread over over 64 load points, and at each load point you define a duty cycle output to drive the boost control solenoid. 0% duty cycle means fully shut and hence nothing reaches the wastegate actuator at all.

Anyway.. of those turbo exec / turbo sri people out there who've done a modification - what have you done and why?

do you get any boost spikes or surges at part load?

No, it's very predictable. Because it's working off the injector duty cycle if you hold the car at a constant load point the amount of boost reaching the wastegate actuator is constant and so boost does not fluctuate.

The boost control strategy is different to what you usually find. In most factory systems, as you probably already know, the boost line from the manifold (or just before the throttle in this case) is connected effectively directly to the wastegate actuator. When the boost control solenoid opens it bleeds air away from the wastegate to the pre-turbo side of the inlet.

In this system you plumb it together differently. The boost line goes into the blocked port on the solenoid, so while the solenoid is shut the wastegate sees atmospheric pressure and stays closed. At load you start to pulse the solenoid and therefore allow boost to reach the wastegate. Apart from giving predictable control over the amount of boost and the shape of the boost curve this also completely eliminates wastegate creep.