The Manual boost controller, Dawes Device or G-Valve, does nothing more than delay wastegate operation. This happens by the valve, which contains a spring and a ball bearing inside a threaded cylinder, lifting the ball off its seat when a certain pressure is reached. The pressure is set using a calibrated boost gauge adjusting the valve. if you set it for a stock 7 psi, then the wastegate will not operate until the 7 psi is reached. This means the wastegate is not modulated by the boost level. If you set it higher, more boost, better performance. This page from the late Gus Nahone will give you an idea. In fact, check out his complete site.

Gus

May he RIP.

I'm not familiar with the bleed system. I'm using a G-valve on my V70 with boost set to 10 psi. Performance is thrilling. I also have a pod mounted boost gauge. The 740 also has a G-valve.
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Warren Bain - '86 744Ti M46 >290Kmi, '99 V70Glt > 45K mi, '96 965 >100Kmi Wifemobile near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu.