How much boost?

[J persons]

How much boost in PSI is generated by a stock 3.5 SHO with a tune? I have a OBD/MX dongle that connects to my cell phone, one of the screens on the app has a boost gauge that goes to 15 PSI. Today I pulled out to pass someone and it pegged past the 15 PSI mark. Would a 30 PSI gauge be enough? Or is the gauge not being truthful to me?

 

[Joshw0000]

The most I've seen is 19.5 PSI with a 3 bar MAP and a few bolt ons. With the factory 2 bar MAP, I believe it should stop around 12ish.

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[BradM]

I hit peaks of 20-21psi but my target is 18psi.