Originally Posted by bradleyland
In what way would it help? What is the benefit of knowing your boost level in a stock car? Once you're modded, I totally understand, but stock, I just don't see the benefit.
Peak boost is not necessarily peak power (horsepower). Peak boost will often correspond with peak force (ft-lbs/newton-meters), but if you're driving for performance, you're more interested in power band and power peak.
If you're interested in knowing where your engine performs best, go do a dyno run. They're usually pretty cheap. If you're running stock, you can just Google image search for 135i N55 dyno and browse the results to get a feeling for where your car is making power.
If you're drag racing, you're most interested in determining shift points. Those are based on acceleration profiles for each gear. Peak acceleration should occur with peak power, so once you have a dyno, you know your shift point (or roughly). With a turbo car, you can sometimes benefit from short shifting a bit. If you really want to know, you get an accelerometer app for your smartphone, and you datalog an acceleration run in each gear. You combine the plots, and you look for the cross-overs. That's your shift point.
Well it would help at the very least in simply knowing that the turbo is at full boost. Just like the red line on your RPM gauge.