If there is a need for some good motorsounds that can be controlled to a certain degree,
this is a good app.
Developed by Audiogaming that make plugins for things like weather, footsteps etc,
that could be considered pricey, the one for making motor noises is just 445 € for example!
This one is for free though and no publicity not even for their own products.
It has a couple of controls and six different motors.
Play Store link:
MotorsMob: car sounds