Quote:
Originally Posted by ps2fixer
Prime example is semi trucks use a jake brake to basically block of the exhaust to increase pressure in the engine and to slow down the truck faster.
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The classic Jake brake actually blows compressed air out the exhaust by opening the exhaust valve during compression -- thus the loud noise. This reduces the air spring effect (where the energy used for compression is returned when the air expands on the down stroke).
Exhaust brakes are more likely to be used on light duty diesels.
I agree that there is not much damage from engine braking with well-designed systems. An exception: On dirt bikes, compression releases used to be common, and they could suck in dirt and do some engine damage.
On ordinary spark ignition cars, meaningful braking requires downshifting, so engine rpm goes up, possibly increasing engine wear more than the brake wear reduction, but I doubt that studies have been done to really quantify the costs. Now engine braking (via downshifting) is not used even in racing, so it is probably a moot point.
For economy, it is best not to brake at all, regardless of the method... unless it's via regen, but even then, coasting is the better alternative if traffic allows.