[Nikolai]

Most important:

Boost gauge: shows, in kPa, bars, or PSI, how much boost your engine is seeing, so that you don't over-boost and blow an engine.

EGT (exhaust gas temperature): Shows how hot the exhaust gases are that are coming out of your engine. This is much more accurate than an 02 sensor, aka air/fuel ratio sensor (unless you have 800 for a wide-range lambda). Generally, if the temperature goes over 1600F, than you're running too lean.

Normal 02 sensors only provide a significant voltage difference around stoichiometric a/f (14.7/1), so you don't know accurately when your engine is rich/lean.

Wide-range lambda sensors provide a nice linear voltage output vs a/f, so they're the only acceptable sensor if you plan on having an a/f meter, but again, they're VERY expensive.

Other good sensors to have would be:

- fuel pressure (esp. if using a fuel pressure riser for fuel management)

-oil pressure
-oil temperature

Good Luck!
Nick