Having had recent boost problem I spoke to Ivan in the parts department at Metro Motors (very helpful guy) and it has come to light that in the pipework to the wastegate actuator there is a small brass olive that restricts the flow to the actuator and makes it stay closed for longer (produces 14psi instead of 7). Now in previous threads I have heard of people complaining of only pulling 7-8psi boost, if you are one of these people check this pipe to see if the restrictor is fitted.....