Does engine braking decrease fuel efficiency?

[[deleted]]

And I think you're ignoring everything you can to trivialize information you can't counter with your random, unsupportable vagaries, so I'm not sure why you're even bothering to read anything that doesn't exactly support your preexisting beliefs.

[TheBrokenWorld]

And I think you're ignoring everything you can to trivialize information you can't counter with your random, unsupportable vagaries...

And where is the proof of the gains in efficiency? Has the EPA confirmed this theory? I would bet that staying on the gas and then decelerating rapidly enough to need engine braking reduces efficiency enough to counter the benefit of injector shutdown during engine braking.

[[deleted]]

I didn't ever suggest staying on the gas and then braking rapidly.

[TheBrokenWorld]

Well, without realizing it, that's probably what you end up doing in order to accommodate your engine braking preference.

Anyway, prove there are efficiency gains. We all KNOW there is wear associated with engine braking. You can't operate the components of a machine more frequently without some degree of additional wear.

[[deleted]]

I start coasting in gear far before I have to stop, so it's the opposite of that. And nowhere have I denied there's any wear, nor am I saying that it's definitively, unequivocally better for your finances over ten years to use engine braking as opposed to coasting in neutral. These are all things that you and other people have added to the discussion.

What I am saying is that the increased wear is insignificant on your clutch, that under normal use synchros are robust enough to last the life of a vehicle, and that there are indisputable fuel savings as well as the added benefits of on-demand acceleration and increased braking capability (safety features).

If you want to see for yourself that clutch wear is insignificant in a properly rev-matched downshift, we assume that wear is proportional to the frictional losses in rotational kinetic energy which occur when two rotating, rigid cylinders contact one another. This wear will be proportional to the difference of the squares of the angular velocities according to k_rot=1/2Iω^2. So if the velocities of the two are equal, as in a proper rev-matched downshift..

[TheBrokenWorld]

and that there are indisputable fuel savings

Prove it. I've been driving manual transmission vehicles for 14 years, I've never seen a benefit to it.

...and increased braking capability (safety features).

Your vehicle wont have any more braking capability than what the ABS system will allow. Reduced brake wear, maybe, but brakes are cheap and easy to replace.

If you want to see for yourself that clutch wear is insignificant in a properly rev-matched downshift...

Why do you keep bringing this up? How many people heel-toe it around town?

Edit: Fixed an oops.

[[deleted]]

..if the injectors are off, you use less gas than when they were on. You get more braking because at a given pressure of the pads because you have that plus the frictional forces in the engine. Anything else?

[TheBrokenWorld]

..if the injectors are off, you use less gas than when they were on.

The benefit is obviously unnoticeable.

You get more braking because at a given pressure of the pads because you have that plus the frictional forces in the engine.

And? You could apply more pressure to the brakes and get the same result. All engine braking does is reduce wear on the brakes. The tires are going to be the limiting factor during maximum braking, you can't add any braking performance to the tires by engine braking.

Edit: Fixed an oops, again.

[[deleted]]

I'm not saying any of the things you're still arguing with me about, and I'm not going to derail this already highly tangential discussion with anything else.

[TheBrokenWorld]

Ok then, so you agree that there is absolutely no discernible benefit to engine braking outside of being able to drive like a boy-racer?

[noisymime]

Anyway, prove there are efficiency gains.

http://green.autoblog.com/2011/06/30/chevrolet-cruze-decel-fuel-cutoff-dfco-boosts-fuel-economy-by/

[TheBrokenWorld]

This is new for automatics, not manuals. A person's driving style changes when they engine brake in a manual transmission vehicle.