I wish theyd change the name of the PBV - its just an adjustable fuel pressure regulator - not so catchy I know but a lot more honest!
On a 16v some people report good gains with a PBV and others dont. This is because of the different states of tune that the 16vs run, including induction and exhaust work, head work etc.
I think if you wanna get serious with tuning a 1.8 16v lump you cant do without a PBV just to give you that adjustability with the air/fuel ratio that you need to get everything spot on. The ECU doesnt have enough control to tackle the fuelling on the edges of its map...eg a high flowing filter, rammed with air at 100mph+, at 6000-7000 revs. The injectors cannot control fuelling simply using a fixed fuel pressure and varying duration under these circumstances...the engine can be seen running lean and this *is* detectable on the road.
The most practical way to get round it is to raise the fuel pressure using a PBV (slightly) then reprogramme the chip to shorten the injector durations when the extra fuel isnt needed. Anyway, hopefully youll get the main point, that a PBV is something to consider once youve done a lot of external mods to the lump but you dont need it before.