All before the patch
All british planes have boost, first you have to engage the "boost cut out" , than you are able to push the throttle from 100% too 110%.
IF there is a boost effect actually, that have to tell you other persons. At least in the Spit II there is a additonal perfomance.
German planes with boost are 109, 87 & 88.
In them you have to engage the "WEP" button.