Quote:
Originally Posted by IronSean
The drag from the moving parts (and it's actually mostly caused by the vacuum created in the engine sucking in air while it moves without fuel) is actually what gives you engine breaking, and can help save your brakes in the process.
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Actually the valves open and close as if the engine is still being operated, due to the camshafts still being directly attached to the crankshaft so it's the compression stroke of the motor slowing the vehicle down as there is very little resistance from the intake stroke (comparatively).
Engine braking to save brakes is pretty poor logic, brakes are cheap to replace whereas using the engine to slow down puts a not insignificant load on the engine and transmission which are much more expensive to replace as they wear out over time. Given the choice to slow down by downshifting vs. using the brake pedal it should be the brake pedal every time.
This argument comes down to how people define 'engine braking' differently. Some guys think it means racecar downshifting to stay in the powerband while others take it to mean (on the city streets) that you're just downshifting per your usual driving rpms (in this car usually between 2k-4k) and a lot of heated arguments result.
I think it's more correct to say "I leave the car in gear as much as possible and when slowing down this results in gas savings because the injectors shut down". At least for daily driving. You don't want to be the guy that's showing off by redlining down to the stop sign bragging about how you're 'saving your brakes' and then you need an engine rebuild well before what is considered normal.
