23.psi on race gas I've been told by SGP..They are great all around turbo's but it depends on what you are after.If you just want a good all around turbo with not much more lag than stock, go for the 500's.If you are willing to do some more intake and exhaust mods you can get 600's to spool almost as fast as 500's..I kind of wish I would have gotten 600's.Speed is addictive..Oh well I'll just wait a while then I'll do the big turbo build up and go all out.I would suggest getting those injectors at the same time. You can usually get a set of nismo 555's for around $850.00,unless you are tight on cash..Good luck on it!! .......