im not totaly sure on the oem gauge but just from experiance with turbo cars you will be doing yourself a major favor by insaling a calabrated aftermarket gauge either on the a-pillar or somwhere on the dash, just because the oem gauges are rarely all that acurate and with a calibrated gauge its easy to dignose problems with the turbo faster. by the way your car stock should run right around 8-9 psi depending if it is a T5 or not.