probly been asked many times but i hav a hawkeye wrx and what is the restricter pill for and is it needed?

 

The pill is in the pipe from the manifold which goes to a 'T' connection, this then goes to the turbo wastegate nipple and boost soleniod. It is used to restrict the pressure from the manifold to the turbo wastegate and soleniod, the smaller the hole in it the higher the boost pressure. I think it also smooths out the changes in pressure these devices see. It cannot be used on its own to tune a car but is used with other mods such as remaps and they are an essential part of a std car's set up. If you've lost it they are less than a £5 from Subaru.

 

Broadly BV has it right, when the boost control solenoid is open, air flows through it from the compressor via that restrictor (or pill, not restrictor pill!), without the flow restriction of the pill the BCS can't flow enough air and therefore won't won't work properly and drop the pressure seen by the actuator below that of the compressor outlet.

Simon