Engine Braking With Manual

[Manorness7]

I am curious to know if you engine brake by downshifting and letting of the throttle completely if it uses more fuel than it would to just use the brakes. And if it uses more or the same amount, how much is it really? Is it worth worrying about? I have been wondering this for awhile since engine braking obviously saves a lot on the brakes... Thanks in advance!

[Petrified.Rabbit]

i am not sure about the aveo, but on a lot of cars when you engine brake, the car uses no fuel. (vw with apr chip for example)

[Manorness7]

That's strange, wouldn't you figure it would use more fuel due to the fact that you're increasing rpms each time you shift? But then again you're not pushing on the throttle to so in a sense the engine is just rotating faster causing more friction, not actually being fueled to do it.

Edit: I found a topic on http://www.dailyfueleconomytip.com:

This is what one guy posted and it makes perfect sense:

Eric April 29, 2008 at 3:04 am

Wow, I was checking out the thread and I can’t believe that people are actually arguing over a common-sense concept! Engine braking is transferring the car’s kinetic momentum energy to the energy needed to overcome the engine’s compression cycle. Since the energy is moving in the opposite direction.. from the transmission to the flywheel, to the crankshaft, to the connecting rods, to the pistions, etc… there is no need for an “explosion” from the piston to overcome the next compression cycle.. the energy is already there (car in motion). To make a general statement that more RPM’s means more gas consumed is really looking at this situation blinded. You can actually cut the gas line to the engine and will continue to run at those high RPM’s as long as the car is still moving downhill. Once the car reaches flat ground it will come to a stop since the energy needed to overcome the engine’s compression will no longer be there.
Maybe the confusion with thinking RPM’s with a moving engine = gas consumption is coming from the ancient days of carburetors which are still used today on our gas powered lawnmowers. The concept there is that the gas is drawn into the cylinder by the “venturi effect” where the air intake for the engine passes over the gas line and creates a gas line suction (kind of like blowing over the top of a soda straw you can see the liquid rise up the straw). So, in this kind of engine.. YES, fuel is consumed whether the engine is actually running by combustion or by being a brake since in both cases air is still being drawn into the engine forcing gas to flow in as well.

THIS IS NOT THE CASE with fuel injection engines. With the ignition turned off ie (fuel pump and injectors not running) the only thing that is entering the cylinder if the engine is in motion from braking the car is air itself.. no fuel at all.

I hope this sheds complete unfiltered light on the topic at hand.


That helped me a lot and I hope that helps other people that may have been thinking the same thing I was. It does seem important to me to know that maybe it isn't such a good idea to do all the time though, because it would put more wear and tear on the powertrain and such. But if you are going down a nice hill and you need to hold your brakes the entire way, it might be better to shift down a gear or two and engine brake.

[ontarian_frog]

At a certain speed, the aveo doesn't use any fuel when you lift off the throttle. Below that speed, the engine will be using fuel, but only to keep the A/F ratio to about 14.7:1. Since the throttle plate is closed, Very little air gets into the engine, therefore very little fuel gets used.

In other words, it doesn't use any more fuel than if you were braking normally and possibly less.

[Petrified.Rabbit]

it does not cause any excessive wear to anything either.

like i said i dont know the exact aveo specs, but lifting off the throttle to brake with the clutch in returns the engine to idle. using the engine rpm to slow down the engine keeps cutting fuel till it reaches idle. so no gas versus idle

[Manorness7]

But powertrain components are still turning (faster), so it's going to wear a little bit more, not excessive wear though like you said. It just won't use fuel to do it, which was the main question I had.

[Pontiac1976]

Well it might burn a little on the sec. But it cheaper and easy to replace brake pads & shoes then trans clutch.
So it all boils down to how long you want the clutch to last.

[ontarian_frog]

If you practice double clutching and matching the engine and transmission speed, the clutch is not even wearing out... I almost always double clutch and match the speed of tranny and engine when I downshift. Makes for a less jerky ride and the clutch doesn't slip while the engine rev's up to match the transmission speed.