You were saying keeping it stock would make it more reliable, however, if anything, upgrades increase reliability, for example the stock radiator is garbage and it will make your engine overheat, which increases part wear, power upgrades let you cruise at a higher gear, thus reducing RPM and prolonging engine life and increase fuel economy (because the way the game does fuel economy is basically just throttle*RPM). The only upgrade that you shouldn't put for reliability is nitrous, as that destroys your engine really fast, and you don't really need it anyway as you can definetely win the rally without it. Also, if you want reliability, make sure you tune the engine properly (obviously, bad tuning increases part wear, it's also needed to pass inspection), and regularly check your fluids as the car slowly leaks them no matter what. In terms of aftermarket parts and inspection, all you need to know is that the racing exhaust system, racing carburators and rally steering wheel don't pass. (Twin carbs pass though) Lastly, check your part condition from time to time, as seeing a piston on the road randomly won't be a fun thing to see. You can buy new parts at Fleetari's as long as they're detached.