the exhaust wont flow as good. i recommend for the best flow is to just take a broom stick and punch a hole in it and make sure it is on the right direction.
+++ If that nonsense is what you think the right answer I am glad there's no chance of you ever working on my car. For a start I doubt it's even possible to fit it the wrong way round, but if it was then it probably would not work correctly so would need re-fitting correctly.
It will tell you it can not read the discc
It is illegal to remove a catalytic converter from any road vehicle.
You cannot physically put a clutch disk in backwards unless you force it together. If you do this you will destroy the clutch disc and possibly other clutch components.
pcv valve wont work properly
It rotates the other way. Yeah, right. You CANNOT put a flywheel on backwards. It's not physically possible to mate the flywheel with the crankshaft unless it is the correct direction.
You could have blown fuses, melted wiring or damaged computers.
You will risk doing damage to the catalytic converter(s).
When you connect the battery backwards you can cause major damage. You can blow the alternator or its fusible link. You can destroy electronics, particularly the various computers - and these are not cheap.
the flywheel in an auto is called a flex plate yes it can be installed backwards, but it will cause problems the ring gear for the starter will not be at the correct distance for starter to engage. the torque converter for the transmission bolts onto the flex plate. the flexplate has balancing weights on it. these weights will be in the way of properly mounting the torque converter
Rotors can only go in correctly one way and will usually snap in place. If you manage to put one in backwards the car will not start and it will likely tear up the cap and rotor.
Most of the time you cannot put these on backwards because the filters normally have a big end and a small end. Most are labeled in and out. But if this happens, the car will not run correctly when it is started because it will not have enough gas.
It will probably overheat. answer= thermostat will not open and will prevent the flow of coolant . which will in turn do damage to your engine