.... if memory serves me correctly.

This means that the total pressure going into the engine with the turbo spun up is going to be 1 bar (atmospheres) for the good old stuff we breathe, plus another 0.65 bar that the turbo gives.

Presumably, the gauge you are thinking of buying starts at zero, and measures the pressure excess above atmospheric. If so, the 1.5 bar max on the gauge will be fine. If, however, I put my Physicist hat on ( I max out at 0.1 Sheldons [big bang theory, late on Ch4 on Tuesdays] ), your gauge reads Absolute Pressure, ie that above vacuum, then you'll run off the end at max boost.