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[acosmichippo]

Hey Everyone

So a while ago I bought my first manual transmission car, and it's been a lot of fun. I've had some experience with manuals on friends' cars, and was familiar with them from general auto interest, so I got the basics pretty quickly. But now I'm researching the topic of engine braking, with respect to safety and general car wear. It has been extremely frustrating, because I've found people equally adamant that either method is totally unacceptable. There are people who swear engine braking is the "proper" way to drive and doesn't wear the engine or transmission at all, assuming you can match the RPM's to the transmission well enough to not slip the clutch [see the top answer on this page]. And then there are people whose arguments seem ok on the surface, but lack any actual evidence, such as "brakes cost less than an engine and transmission, so I don't engine brake" or "engine braking doubles the wear on the transmission because you use it twice as much".

Anyway, just wanted to pose the question here, because I know there are a lot of car enthusiasts, and a lot of you really know your s***.

[scotty]

I don't see why there would be a problem, if you did it properly, matched the revs appropriately and such. If not you could damage the clutch, or far more likely just wear it faster (i think this is the biggest potential problem area). I think the one thing about engine braking however, is that you might use a little more fuel. Emphasis on a little.

"engine braking doubles the wear on the transmission because you use it twice as much" - yeah this argument makes no sense, cause you aren't actually using it any more times Still one gear shift to change gear...

Don't take what i say here as gospel cause i never really looked into this exact thing myself, but the above is my conclusion by my logic.

I engine brake some times and not others, depends when i can be arsed...

[acosmichippo]

The topic of fuel efficiency is one that I actually did find an answer to.

Modern electronic (as opposed to mechanical) fuel-injection systems (that also includes TBI (throttle body) single-point injection) are equipped with throttle position sensor. In the event of overrun (higher RPM, closed throttle) fuel input is cut off, thus making it more efficient than coasting in neutral and using brakes alone (one supposed to brake with gears engaged anyway). Fuel kicks in only when engine speed (RPM) approaches to or below the idle speed to maintain it.

Information about fuel cut-off operation can be found in Bosch technical publication “Gasoline Fuel-Injection System K-Jetronic” (PDF, search for multiple occurrences of “overrun”):

Fuel metering is interrupted during trailing throttle [overrun]. Although this expedient saves fuel on downhill stretches, its primary purpose is to guard the catalytic converter against overheating stemming from poor and incomplete combustion (misfiring)

[…]

Cutoff of the fuel supply during overrun operation permits the fuel consumption to be reduced considerably not only when driving downhill but also in town traffic.

Similar data can be found on systems of other manufacturers. Some of them even allow the cut-off parameters to be modified (see adjustment of overrun for SManager software for s300 module for Honda ECUs — good illustration on how this feature works).

[bud]

having only ever driven manual cars i tend to have found engine braking does eventually put extra strain on the drivetrain and engine mounting. Think of the force required to slow the car down, the energy has to go somewhere, and if the brakes aren't taking that energy where do you think its going to go?

[Jabberwocky]

Engine braking all the way. I was told by my driving instructor, brakes are used in 3 conditions.
1 on hills
2 an emergency
3 when you did not anticipate the road enough


using phone, so beware of predictive text errors.

[bud]

Engine braking all the way. I was told by my driving instructor, brakes are used in 3 conditions.
1 on hills
2 an emergency
3 when you did not anticipate the road enough


using phone, so beware of predictive text errors.

your instructor wasnt a drunk was he?

[What's Burning?]

couple of points... automatic transmission also engine brake. The next time you're in an automatic car get it up to speed and then simply take your foot off the gas preferably on a level road and see what I mean.

The point of downshifting (I hate the term engine barking) is to keep the car as settled as possible. With downshifting you're able to maintain more speed in most situations.

Additionally, if you've ever heard the term heel and toe, then you know it's done all the time by pros and that basically all it is is a form for using both the brakes and the engine to manage a car through a turn. Key word being "both".

Lastly it all depends how you drive, but in the end you'll spend a hell of a lot more money if you're constantly bringing a car from 90 down to zero than from 90 down to zero with a couple of downshifts in between.

[scotty]

having only ever driven manual cars i tend to have found engine braking does eventually put extra strain on the drivetrain and engine mounting. Think of the force required to slow the car down, the energy has to go somewhere, and if the brakes aren't taking that energy where do you think its going to go?

A valid point, but it is still completely possible to use engine braking while staying well within stress and strain limits of the parts.

[What's Burning?]

if the brakes aren't taking that energy where do you think its going to go?

I'd say most of the energy is going into compressing the air fuel mixture in the cylinders. There is some energy absorbed by and dissipated as friction and heat by the drivetrain but that's no different than the energy that drivetrain would absorb under acceleration.

My point is, that you can save/prolong both by using both. You're also able to control and accelerate a car a hell of a lot better through turns with engine braking.

[acosmichippo]

if the brakes aren't taking that energy where do you think its going to go?

I'd say most of the energy is going into compressing the air fuel mixture in the cylinders. There is some energy absorbed by and dissipated as friction and heat by the drivetrain but that's no different than the energy that drivetrain would absorb under acceleration.

My point it, that you can save prolong both by using both. You're also able to control an accelerate a car a hell of a lot better through turns with engine braking.

This is close to what I have found so far too.

Engine Wear

As above suggests, power stroke is eliminated, ergo one of the most demanding energy loads on the engine is gone. In all, given proper care and maintenance, consensus is that engine braking does not add any statistically significant friction wear on the motor itself.

To test this hypothesis I did several searches on the subject via academic databases and Google Scholar (both with and without patents), and I have not found a single paper concerned with increased engine wear, but plenty discussing the methods to increase effectiveness of engine braking, as power of modern engines increased dramatically, and drive-train losses are reduced. As this U.S. Patent 5,146,890 (by Volvo) states (p.1 of “Description”):

When driving in hilly terrain, the wheel brakes should be used as little as possible, primarily for safety reasons. The average speed of the vehicle in hilly terrain is therefore greatly influenced by the available engine braking power, which increases the requirement for a more effective engine brake that will also be capable of reducing wear and tear on the wheel brakes and thereby improve running economy.
Gearbox Wear

Higher RPM by themselves do not mean that gearbox is being pushed beyond its design limitations. Few hills at higher RPM due to engine braking (given smooth transitions when switching) would not cause any more wear than, say, hours on end on the motorway pushing over 120 km/h (75 mph). If mountain roads is your primary area of operation then it would qualify as severe use (just like frequent towing), and would require transmission cooler anyway.

[darwin dali]

The point of downshifting (I hate the term engine barking)

I think that describes it pretty well though

[Jabberwocky]

Braking is wasting fuel, and therefor cost money.

[acosmichippo]

Or alternatively, "'over-accelerating' is wasting fuel".

[What's Burning?]

Define waste. Time is money and so getting there faster is a cost offset. Actually the more you earn the more you save by going faster.

[Jabberwocky]

better late in this world than early in the next