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How could engine braking save fuel? Using any type of brake retardation is a waste of momentum and thus a waste of gas.Roland Ehnström wrote:About saving fuel, eco-driving shools actually teach you to use as much engine braking as possible. It actually saves fuel - and also gives you less brake wear. This is one of the (several) advantages of stick-shift versus automatic gearboxes.
A modern engine, when on over-run (i.e. coasting with no throttle) uses zero fuel (the only reason it turns at all is the torque produced by the driving wheels). If you were to do the same thing but with the clutch depressed then the engine would use some fuel keep the engine at idle - to not stall.ISLAMATRON wrote:How could engine braking save fuel? Using any type of brake retardation is a waste of momentum and thus a waste of gas.Roland Ehnström wrote:About saving fuel, eco-driving shools actually teach you to use as much engine braking as possible. It actually saves fuel - and also gives you less brake wear. This is one of the (several) advantages of stick-shift versus automatic gearboxes.
How could engine braking be more fuel efficient than foot braking? Fuel flow continues even at zero throttle so unless you turn off the ignition and then use the foot braking the next most fuel efficient way to brake is to throw it in neutral(whether in an auto or manual) and use the foot brake. But, we all know engine braking saves the brakes, but I dont do it(on the street) because that adds duty cycles to the engine and trans which happen to be alot more expensive to change than the brakes(which are designed to be easily changed).
Please provide your reasoning as to why engine braking gives higher gas milage, only thing I can think of is in a hybrid car, letting it "coast" actually activates the regen braking.
Edit: I see Ciro actually asked you first Roland.
I love being rightmajicmeow wrote:On all modern vehicles, the fuel injectors are actually shut off when the vehicle is coasting (or braking) IN GEAR. The engine does not need to fuel to continue rotating, as the mechanical connection to the wheels via the transmission keeps the engine moving.
If the vehicle is put in neutral or the clutch pedal is pressed down, the mechanical connection to the wheels is disrupted and the only way for the engine to continue turning is by restarting the injection process.
This method has been used on cars for several years now on many many different makes from Toyota, KIA and BMW to many exotic brands as well.
I dont know how modern a car you are talking about but no car that I have ever tuned completely turned off the the injectors on overrun... and I have personally watched the injector duty cycles on a engine scanner. On cars that I personally tune I do turn off the injection pulses during overrun, but I usually ask my customers first because most people are not used to the feeling of that much engine braking coming on so suddenly, it makes for a rather jerky ride that the manufacturers try not to have.majicmeow wrote:On all modern vehicles, the fuel injectors are actually shut off when the vehicle is coasting (or braking) IN GEAR. The engine does not need to fuel to continue rotating, as the mechanical connection to the wheels via the transmission keeps the engine moving.
If the vehicle is put in neutral or the clutch pedal is pressed down, the mechanical connection to the wheels is disrupted and the only way for the engine to continue turning is by restarting the injection process.
This method has been used on cars for several years now on many many different makes from Toyota, KIA and BMW to many exotic brands as well.
I'm talking BMW's, Toyota's, Honda's etc of the last 2-3 years. My 2008 Yaris does it, ALL new BMW 6 cylinder's do it, I've "heard" (yes, just heard) that the new honda iVtec engine also does, but I cannot verify this for sure. The new Audi's petrol and diesel engines do it (as of 2007 if I remember), so how modern do you need? How do you think manufacturers are getting 300hp from a 3L engine and still making 30+ MPG??ISLAMATRON wrote:[I dont know how modern a car you are talking about but no car that I have ever tuned completely turned off the the injectors on overrun... and I have personally watched the injector duty cycles on a engine scanner. On cars that I personally tune I do turn off the injection pulses during overrun, but I usually ask my customers first because most people are not used to the feeling of that much engine braking coming on so suddenly, it makes for a rather jerky ride that the manufacturers try not to have.
The effect is NOT harsh, it does NOT come on suddenly and it does NOT make a jerky ride. The engine is being overrun regardless. Fuel is usually transitioned off. If the ECM requires, it keeps the injectors running. I dont know why the ECM does some of the things it does lol :p. Driving a BMW 6 cylinder is to be driving one of the smoothest and most refined engines being produced today. They also get the best fuel mileage for an engine in their class.
When you talk about "tuning", what kind of vehicles are you working on? 
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