heres a bit i wrote about amals a while ago...



Amal valve,or boost control solenoid as its sometimes called, this is how the ecu controls the amount of boost the turbo makes ,like an elactronic bleed valve in effect.

it also allows the boost to have a peak and hold figure, as the boost will spike when the valve is opening, then return to its hold figure when it closes off at the top of the boost range.

some people do away with them and just fit a bleed valve in between, but then you can only run the hold figure of boost and not have a nice spike to give a tad more torque where its needed

the amal valve basicly stops the wastegate actuator seeing the full amount of boost pressure coming from the compressor housing ,it does this by opening and closing a electronic valve, which bleeds some of the boosted air to atmosphere



take this example ,your wastegate actuator is set with a small pre load, and will open at 15psi.

the turbo is making 15 psi, so the wastegate should open preventing the turbo from making any more boost, BUT the amal valve is opening and closing very quickly allowing 5 psi to escape to atmosphere, all of a sudden your turbo is making 20psi before the wastegate actuator can see the 15psi it opens at. HERE IS YOUR PEAK FIGURE,

Then as the rpm climbs ,the ecu tells the valve to stop opening and it stays closed, the wastegate actuator can now see the full amount of boost made by the turbo and only allows 15psi before it opens the wastegate to prevent any more, HERE IS THE HOLD FIGURE.
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