I've got a '94 STi I, and as far as I know, it has the standard recirculating dump valve. I do notice that the turbo takes a bit to spool back up after a gear change. Will a new dump valve make a noticeable difference to this? Just a bit wary of sounding like a muppet - don't want a really loud PTSHHHHH!

 

You can buy an aftermarket recirculating dumper too, they dont all vent to atmosphere (ptshhhhh)

 

Yeah, but would it make any difference?

 

Louder the better...

 

It can make a difference, yes, but it's subtle.
I didn't really notice it until I changed back to the standard - at which point I put the aftermarket one straight back on again!

I have a feeling that many of the aftermarket BOVs are simply there to please those who want a noise & aren't interested in the potential 'between gears' improvement. I have only used the APS & HKS models - the HKS can be made to recirculate & is noticeably better than the standard one - but is seriously expensive! The APS one is a good half-way house: I don't think it's as 'quick' as the HKS (but I'd grown used to the HKS by then, so my standards had changed somewhat), but it's quite a bit cheaper AFAIK & recirculates from low boost & dumps to atmosphere at high. It's also not too noisy when dumping to atmos, which is a bonus.