4 ms·

When you coast with engaged clutch, you will engine brake True Energy doesn't go to the engine for free. Adding the fuel to counter the engine braking i

When you coast with engaged clutch, you will engine brake True Energy doesn't go to the engine for free. Adding the fuel to counter the engine braking is less efficient than letting the engine run idle while coasting due to losses in the power-train It is a bit hard to understand where you're trying to go here but assuming that you state it takes fuel to 'counter the engine braking' you're wrong. Engine braking is just that, using the engine as a brake. The engine is used as a pump, air (and only air, no fuel is added) is compressed, the air heats up, this heat is dissipated by the cooling system. That is where the energy actually goes, as heat. Losses in the power train only add to the braking effect. This is also why it is a bad idea to use engine braking with a 2-stroke petrol engine: 2-strokes rely on oil mixed in with fuel for lubrication. When using the engine as a brake no - or hardly any - fuel is added to the incoming air while maintaining high engine speeds, starving the engine of lubrication.

Dylan16807 10y ago
They're talking about the situation where you're coasting and don't want to brake.
3poundkilograms 10y ago
It's a bit hard to understand where you're trying to go here but assuming that you state it doesn't take fuel to "counter engine braking", you're wrong. Engine braking is just that, using the engine as a brake. If no fuel is added, pumping losses will make it act as a (relatively weak) brake. If you want to coast without braking, with the clutch engaged, you will need to inject fuel to counter the pumping losses of the engine, losses which are higher if the engine is not idle. Losses in the power train add to the braking effect, which must further be counted with additional fuel. If you're going downhill with clutch disengaged and maintaining your speed, engaging the clutch will very likely increase your fuel consumption for the same task (maintaining speed). Automatics have a coasting gear (usually the last or only overdrive gear) for this very reason. (Sorry, I had to do that.) Side notes: 1. Coasting is not braking. People seem to be mixing "coasting to a stop" and "coasting" in general. Engine braking, when your intention is to reduce your speed, is more efficient than friction brakes, but coasting does not mean that you intend to reduce your speed. 2. Who drives a car with a 2-stroke petrol engine? :)

Dylan16807 10y ago

They're talking about the situation where you're coasting and don't want to brake.

3poundkilograms 10y ago

It's a bit hard to understand where you're trying to go here but assuming that you state it doesn't take fuel to "counter engine braking", you're wrong. Engine braking is just that, using the engine as a brake. If no fuel is added, pumping losses will make it act as a (relatively weak) brake. If you want to coast without braking, with the clutch engaged, you will need to inject fuel to counter the pumping losses of the engine, losses which are higher if the engine is not idle. Losses in the power train add to the braking effect, which must further be counted with additional fuel. If you're going downhill with clutch disengaged and maintaining your speed, engaging the clutch will very likely increase your fuel consumption for the same task (maintaining speed). Automatics have a coasting gear (usually the last or only overdrive gear) for this very reason. (Sorry, I had to do that.) Side notes: 1. Coasting is not braking. People seem to be mixing "coasting to a stop" and "coasting" in general. Engine braking, when your intention is to reduce your speed, is more efficient than friction brakes, but coasting does not mean that you intend to reduce your speed. 2. Who drives a car with a 2-stroke petrol engine? :)