csburdick

REV App Turns iPhone Into Performance Driving and OBDII Diagnostics Tool I see you're a skeptic in all aspects ;) Horsepower can be estimated based on weight of the vehicle and velocity. HP is usually calculated based on torque as you said, but can be estimated if torque is not known, based on your speed after a certain distance - say, a quarter mile.

REV App Turns iPhone Into Performance Driving and OBDII Diagnostics Tool It's very useful to be able to clear check engine codes when diagnosing a problem. For example, if you get a check engine code that is a temporary problem and fixes itself, many times the code won't clear itself even though the problem is fixed. Also if you've replaced the part that caused the light to trip, you want to reset the code and drive for a bit to make sure the code doesn't exist any more.

REV App Turns iPhone Into Performance Driving and OBDII Diagnostics Tool Bristol: It reads directly from the OBDII port, and many cars provide MPG readings through it. It's not an estimation; it's what the car is telling the device that it's getting. Also, not all readings are available for all cars through this device, so if the car's CPU doesn't read MPG, it won't display on Rev.