Sure. In theory, it's really simple... but the mechanical portion of it can make or break the setup.
Originally Posted by turbo2.24.1990
A microswitch is placed in just the right spot so that when you're in first gear, the switch is engaged. Thus, when you're in 1st gear, the switch is on... and when you're in any other gear, the switch is off. If you wire the switch up to your multi-stage boost controller in the right way, you can have it trigger one stage of the controller (in this case, the low boost stage) and then when its off, have the other stage kick in giving you full boost.
This could be achieved pretty simply. If we operate on the idea that the "stage" with the lowest boost will always "win" (as in the lowest boost stage will always trigger the WG first) then we can use a manual boost controller to limit our maximum boost and use a simple solenoid valve to control the low stage, or even multiple stages.
Picture it as such:
The solenoid, "max boost" MBC and N75 valve all get the boost source from a tee. Their output is also merged with a tee and goes back to the wastegate.
Boost Source ---> MBC (max boost) ---> wastegate
solenoid (with another MBC inline)
The solenoid has a MBC inline with its output. This MBC is how you set your "low boost" stage. The microswitch, when you were in first, would trigger the solenoid "on" and let the boost pressure hit the MBC, which once it exceeded the low boost setting, would feed the full boost pressure to the WG and thus opening it and limiting boost.
In all cases, the "max boost" MBC will always feed pressure to the WG when hit. If you're under max boost, though, your boost level will then only be able to be limited by the MBC behind the solenoid... and only if the solenoid is energized (on).
You get the benefit of part throttle control via N75 and the benefits of the a hard cap on boost (overboost protection) along with your 1st-gear-limited boost control via the microswitch/solenoid.