Coasting or Engine Braking: Which Is More Efficient?
When you’re out for a blast through the canyon, you can consider philosophical questions, like efficiency in a Corvette.
We ran across a YouTube video from Jason Fenske at Engineering Explained that answers a question we’ve had for a while: Is it more efficient to coast or engine brake down a hill? Now, the debate isn’t totally settled, since he narrowly focuses on what is more ‘efficient’ and ignores the other factors. But, call us more informed.
To start, he notes that his findings only apply to modern cars with electronic fuel-injection. Jason is driving a 2016 Subaru Crosstrek with a manual transmission, but the same principle applies to modern Corvettes with the manual or automatic. What did he find out? It’s more efficient to engine brake, than to coast.
When you coast, the engine uses a tiny amount of fuel to keep the engine idling. If you have ridiculous cams, it uses even more. When you engine brake, the computer shuts off the fuel injectors, which means the engine is burning no fuel. Gravity keeps the car moving down the hill, while the engaged transmission means the engine keeps turning, along with all its accessories, all the while not burning a drop of fuel.
Though it is more efficient on a straight hill, there is a situation where coasting is more efficient. When going down a set of hills that are consecutively smaller, letting the car gain speed while coasting lets it make it up the next hill without having to put the car in gear. Think rollercoaster. If you were engine braking you’d use no fuel going down the hills, but would invariably use lots of fuel going up the next one.
The real answer to which is more efficient is, to quote Jason, “It depends.” Though driving your Vette efficiently just doesn’t sound like a good time, it’s a good way to keep track of overall engine health.