Electronics 2000

This is for automotive use, for exhaust systems.. Having a butterfly valve which opens or blocks the exhaust to affect noise volume but unsure of how to control said butterfly valve

i need something that can allow the value to turn 45 degree's but also allow to be set at a degree between 0 and 45 for different exhaust tone

Any idea's??

You could use a stepper motor, but this gets complicated very quickly and probably requires a microcontroller in order to make it work well. One of the complications is that each time the circuit starts up it has to reset the position of the stepper motor.
Also consider that anything you fit in a car has to be pretty resistant to hostile environmental conditions (temperature, humidity, vibration, interference on power supply).

Me, I'd use a bowden cable and a bicycle gearchange lever