How is this done ?

 

could be a simple amal valve on/off switch for next to nothing,

 

I dont think i have an amal valve ????

 

If you have an RST you have an amal valve as standard

 

it may have been by passed at some point

 

mine got by passed as many do when they fail.running of in car bleed valve wich is always on full as my car is unchiped so only runs just over7 psi

a dodgy amal valve can give u varied boost levels before a tuner bypassed mine it was running 4.3 psi

 

i looked today and i dont see an amal valve the pipe from the metering head as just been blobked off