As far as I know its not a problem on gr. My last tune made 270whp at 19psi, my mate made 295whp (1000cc injector)at 22 psi on oem pump.

Ive seen a 08sti with cracked ringland that tuner has to retard timing to avoid further damge, which resulted only 290whp with td06-20g, but his peak torque and power were very close unlike op's dyno graph. Give mao a call just to get a second opinion maybe?

using the Perth-WRX mobile app

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport