sry guys but there is no magic number the stock valve is going to hold. if it leaks, it leaks. to the OP find a stock valve and try it out. if it works then you're fine, if it doesn't then get an aftermarket one. i'm not sure why you would have a valve that ONLY holds up to 14psi unless it's faulty and leaks past that boost. could be you just need to adjust the spring with a shim or maybe it's a china made pos. either way as you can tell everyone has their own opinions but ideally a stock valve should be fine. the real question is what else is done to the car? on an otherwise stock wry i wouldn't advise you to go past 16psi. you won't be efficient really at anything over that and are just raising the charge temp and losing power. now if you got some decent mods then it may be possible to run 18psi with some benefit

 

Spector intake
Grimspeed turbo inlet pipe
Forced performance 68 hta turbo
Perrin downpipe
hks hi power exhaust
Hks up pipe
Turbo xs frontmount
Ported throttle body and intake manifold
Deatschwerks 750cc injectors
2 step colder ngk spark plugs
Aps lightwieght flywheel
Exedy stage 2 clutch kit
Unorthodox racing lightwieght under drive

 

Turbo xs bov