[aleh]

When breaking with engine, the kinetic energy of movement is converted to heat not via friction (like breaks do) but via compressing air in cylinders which does not cause extra wear on anything.

[CoffeeDregs]

I think you're referring to "Jake Braking", which is very noisy and is banned in many towns (in California).

https://en.wikipedia.org/wiki/Compression_release_engine_bra...

[Unklejoe]

"Jake Braking" is similar, but pertains more to diesel engines which have a special valve to support this since they work differently.

Engine braking on a gasoline engine is actually quieter than normal operation.

[mmagin]

At least the manufacturers of those products assert that correctly installed ones are no louder than the diesel engine in normal operation.

http://www.jacobsvehiclesystems.com/about-us/environmental-h...