hi all,
i'm a new member, i've had 3 imprezas and just bought my forth, a 51 uk300. this seems to be a good forum with lots of noligable folk. a quick question , feel free to rib me if its a silly one.
whilst the turbo is winding up the dump valve seems to be releasing air at full throttle, is this normal as i have never had a dump valve do this before. i don't know what valve it is but the previous owner was told it was a good one..

 

Sounds like the dump valves spring is weak as the dumpvalve should only dump when you release the throttle, if your on full bore and have reached max boost the only thing that should be releasing should be the wastegate.

Oh i forgot to ask if this was the standard dump valve? or aftermarket?

 

it is an after market valve, it has GFB stamped on the front, here is a pic

 

And your sure it's not the wastegate thats dumping due to to reaching max boost?

 

i don't think so, it starts hissing at low revs, theres no way its up to full boost when it starts hissing..
i have searched for the company on google, the valve is a hybrid so you can either have it dumping air to atmostsphere or a 50/50 recurclation. it all seems odd to me.
has any one else on here have a gfb hybrid dump valve?

 

TBH i have never heard of them, and it may be that the spring inside is keeping the DV open therefore venting air. Which either means it needs adjusting or changing.

 

gfb stands for "go fast bits" they are a good company, and i have heard good things about them, however i cant shed any light on your problem, sorry.