Talk:Engine braking

vacuum
Can someone write up more information on how and why this "vacuum" inside an engine magically slows a vehicle more than friction with the drive train? As someone who's generally competent--although inexpert--with physics, this sounds like a load of bullshit, so I'd appreciate more actual detail with useful information here. :)

'''Vacuum or compression has nothing to do with engine braking. Diesel or Otto engine never mind. Energy spent to create vacuum or compression is conservative and returned in the very next expansion. Just like any spring. Engine braking comes mainly from internal friction. Small part of it comes from pumping losses (air flow). Completely different thing is engine brake system on a big truck engine. It basically converts engine into a big compressor while braking. This whole page has to be rewritten. As it is it doesn't belong to any encyclopedia.'''206.116.101.49 (talk) 17:04, 21 February 2012 (UTC)


 * I'm not certain the article as-is reflects what's happening. There is an easy test for this, which I have done in the past on a friend's classic Mini which I had to turn over by hand to get the engine turning.


 * With the carburettor in place, and the spark plugs removed, I was able to turn the engine by hand. This was because the engine cannot compress any air when the plugs are removed. With the carburettor removed, and the spark plugs in place, it was impossible to turn the engine by hand. This experiment would appear to suggest that out of the "Suck Squeeze Bang Blow" of the four stroke cycle, it is the "Squeeze" rather than the "Suck" that causes the majority of the engine braking effect in a gasoline engine.


 * If you have a carburetted engine the same test can be carried out while on the move. Shut off the ignition while travelling down a hill. If you open the throttle at this point, the article suggests that any engine braking will be lost. This is not the case.


 * The rotational energy of the drivetrain is being converted into heat energy by compressing the air, and that energy is not fully recovered by the subsequent downstroke since the engine is designed to remove as much heat from the pistons as possible at all times, causing the temperature to drop, and the piston to be at a slight vacuum by the bottom of the downstroke. That's on a gasoline engine. The same is true on a diesel engine.


 * Any confusion here is with the addition of the "Jake Brake", which according to their website cleverly actuates the exhaust valve much earlier in the cycle, where "bang" normally would be. This releases the compressed air when it holds the most energy, and then closes the exhaust valve again, causing that piston to have to work against much more of a partial vacuum in the cylinder on the downstroke. That massively increases the braking effect.


 * JN5556649 (talk) 22:12, 17 January 2011 (UTC)

Where does waste heat go when creating a vacuum? While friction and drag from accessories contribute, much of the force in engine braking is due to pumping losses, with the cylinders trying to draw a vaccum against the closed throttle (as well as pushing air past the valves). Instead of the pistons pushing on the connecting rods, the connecting rods pull the pistons down. Vacuum braking force for each cylinder would be Patm-Pcyl * piston area. Drawing a vaccum actually cools the air though. The kinetic energy of the car must ultimately be converted to heat and be disappated into the air (presumably through the radiator and/or exhaust), but where in the process of creating a vaccum is the heat made and how is it rejected.--129.238.237.96 (talk) 18:22, 15 September 2011 (UTC) — Preceding unsigned comment added by 129.238.237.96 (talk)

Engine braking in a gasoline engine has nothing to do with intake vacuum; it is due to compression. This can be easily verified in your car by shutting off the ignition while keeping the throttle wide open. The car slows down just as much with the throttle open as with the throttle closed. — Preceding unsigned comment added by 70.71.27.207 (talk) 09:02, 29 December 2011 (UTC)


 * Your experiment will actually support the opposite of your argument. If you shut down a gasoline engine and open the throttle, the engine will run on longer than with a closed throttle - this is very noticeable if the vehicle is moving when you do it (don't try this at home, folks!).  It IS the restriction in the inlet that creates engine braking, not compression effects.  Yes, it is hard to overcome compression effects if starting from stationary, but once an engine is running and the flywheel has stored energy to smooth out the lumps, the 'effort' you put into compressing a charge of air will almost all be got back as a 'spring' effect.  You will lose a little energy through friction and heat losses, but negligible compared to the throttling effect in the intake. Weasley one (talk) 15:33, 17 December 2012 (UTC)

A major loss is from pumping air (moving mass is doing work). If the carb was sealed shut it would drag less because no air would be pumped. So 'vacuum' from a closed throttle certainly does not slow it down 'more'. Think of putting your hand on the end of a vaccum cleaner hose, the motor speeds up because it's doing less mechanical work. It would be helpful if someone would demonstrate this on youtube, drive an unfueled engine via prime mover whose wattage can be measured, try with throttle open, throttle shut, and valves stuck open. 146.115.72.218 (talk) 00:52, 1 April 2016 (UTC)

Some confirmations/clarifications/points: 1) The friction of the drive train plays very little part in engine braking, in fact the car industry has been actively reducing any source of friction in the drive train as much as possible! 2) The compression does take a lot of energy, BUT you get almost all of it back again, when it springs back during the expansion phase (EXCEPTION: If a 'jake-brake' is involved, as it releases all that compressed air and all the energy in that 'squashed air' is lost! Just to clarify, jake-brakes don't count here as they are an extra thing added to the engine. It's bloody confusing that in the US, when people talk about 'engine braking' they're usually talking about jake-braking!)

Regarding the use of the word 'vacuum', I'm coming round to the fact that it is slightly misleading; I have used the term because this is how it was explained to me, but reading your comments here, I think 'air-flow restriction' might help help people understand better; The simile in the Petrol section about the effort needed to suck air through a narrow straw vs. a wider one perfectly illustrates the core principle behind engine braking.

If you've ever driven an old diesel before they started blocking up the exhaust pipes with DPFs and EGRs and Turbos and such, you'd find that they can roll in-gear for a lot longer than petrol engines because they didn't have that air flow restriction sapping energy. This is also why diesels need vacuum pumps for the brake booster as they can't just tap off the throttle vacuum like petrol engines can.

Newer diesels feel like they have engine braking like petrols do, due to the afore-mentioned obstructions in the exhaust cause similar air-flow restrictions. I know in mine the car will coast for ages until the rpm drops too low and the turbo stalls, at which point there is a noticeable increase in drag.

For added confusion, I've noticed some petrol engines actually fully open (or shut) their valves when coasting and DFCO is active to avoid this air-flow restriction loss; Just one of many tricks petrol engines are using to try and get their efficiency up to diesel levels!

NB: When I say coasting, I mean lifting off the accelerator pedal *while in-gear*; Never coast in neutral or with the clutch pushed in! It's dangerous because a) You're no longer in full control of the car (No acceleration!) and b) If you're silly enough to do that, you're probably silly enough to try and re-engage the clutch without sync'ing everything up and risk over-revving the engine or frying the clutch! (Like if you accidentally go from 5th to 2nd instead of 4th, but worse) 77.102.205.126 (talk) 22:00, 7 September 2016 (UTC)

I have added a source to back up the claim that manifold vacuum is the source of engine braking in a gasoline engine. It seems like there was some controversy and some people are claiming that compression plays a role in engine braking which is false. Its a common misconception that I myself shared up until a couple of months ago.ApollosEclipse (talk) 02:58, 16 December 2019 (UTC)


 * If you look at the four cycles of a gasoline engine, you will find a simple answer:
 * 1) Intake stroke: with the throttle closed, the piston pulls against the vacuum in the manifold. This creates a
 * 2) Compression stroke, the force is reversed and the piston is pulled back towards top dead center with nearly the same force as was exerted on the way down. Like a reverse air spring. This creates a  and thus strokes 1 and 2 largely cancel each other out.
 * 3) Power Stroke: The piston travels down again, but there is no combustion, so the piston is pulling on the vacuum in the combustion chamber This creates a
 * 4) Exhaust stroke: The exhaust valve opens and air is allowed to enter the cylinder (reverse-flow from the exhaust system which is at ~1 ATM). This relieves the vacuum that was going to pull the piston back up. As the piston approaches TDC, this air is expelled again. This creates a 
 * Note that of the four cycles, we have (-1,+1,-1,0) Two of ths cycles cncle each other out (you can pick which ones), and one is zero, so we are left with just one cycle of net negative torque caused by the negative pressure on the top of the piston relative to the bottom of it. THIS is where engine braking comes from.
 * By relieving the vacuum in the cylinder, the exhaust valve opening at BDC acts like the inverse of a jake brake, effectively blowing off vacuum rather than blowing off compression.
 * So yes, it is not just vacuum, but the fact that vacuum is suddenly lost at the exhaust stroke that causes the net negative torque during engine braking.
 * It is also worth noting that an open throttle will change this radically; it only works if there is a vacuum developed on the intake stroke. Gary505 (talk) 03:57, 2 July 2024 (UTC)

reworking
This page needs reworking, in my opinion, and I'll try to do so soon if there are no objections. In an engine, the compression of air in the cylinder is approximately a reversible process. Yes, it takes energy to compress it on the compression stroke, and the gas heats up, but on the downstroke that energy is returned to the crankshaft and the gas cools back down. In a gasoline engine, engine braking during closed-throttle operation comes mainly from maintaining a partial vacuum in the intake manifold (between the closed throttle and the cylinders). Diesel engines are unthrottled, so they don't incur these "throttling losses" and don't provide much engine braking (it's also one reason they tend to be fuel-efficient); a jake brake on a (presumably diesel) truck provides engine braking by opening the exhaust valves at the top of the compression stroke, so that the energy used in compressing the air is lost, instead of being returned to the crankshaft. - Coneslayer 05:01, 2005 Mar 5 (UTC)

Sounds like you know about the subject, no objections here. Raazer 16:44, 8 Mar 2005 (UTC)

I agree - the article as it currently stands is completely wrong. Engine braking is the term used to describe the retardation effect when the driver lifts off the accelerator. As has been stated above and below, this is NOT from compression of the combustion charge, but from throttling effects in the air flow pathway. It appears that I am commenting nearly 3 years after the above and yet the article currently continues the phallacy of engine braking and compression. There are compression braking mechanisms, as described elsewhere, but the simple "lift-off" braking effect commonly known as engine braking is not correctly described. —Preceding unsigned comment added by Weasley one (talk • contribs) 15:24, 25 February 2008 (UTC)


 * Just checked back here and now fully happy with the article as written today! :) Weasley one (talk) 13:14, 4 June 2010 (UTC)

In order to slow down a car, you have to do work. Kinetic energy has to be taken out of the vehicle and moved somewhere. Having a (partial) vacuum on the inlet manifold will exert a force on the engine, but there is no energy entering or leaving the manifold as long as the partial vacuum remains fairly constant. Not so the cylinders. With a compression ratio of (say) 10, the air being sucked into the cylinder will be compressed around 10 times. Assuming an adiabatic compression, that would put up the air temperature from 300K to around 3000K. The heat transfer from the hot air to the cylinder head will be very good because the air molecules are hitting the cylinder head faster and faster and more and more often as the space above the cylinder contracts. As this air cools down during the expansion cycle the transfer of thermal energy from the cylinder head is not so good because the air molecules are hitting the surface less and less often and moving slower. You can do the same experiment with a bicycle pump. Just close off the outlet and pump away vigorously for a minute. You will notice that the pump warms up quite a lot (as will the pumper!), because the compression and expansion cycles differ in the way that the heat is transferred to and from the pump walls. The theory about the inlet manifold pressure slowing the engine is confusing force and energy. My chair is exerting a force on my backside to stop me falling to the floor, but there is no energy transfer. To move (kinetic) energy out of the car (braking) you have to do work. — Preceding unsigned comment added by 2A02:810B:87C0:CE4:173:3864:FC77:700E (talk) 02:30, 29 October 2020 (UTC)

Brakes, brakes, brakes
OK, we've got Engine brake (AKA Compression brake), Exhaust brake, Air brake (rail), and Jake brake (plus multiple suffixes for each e.g. -e, -es, -ing). Is there a better way to organize it? Just adding a category might not elucidate one as to the differences, if there are any, between the various types. Ewlyahoocom 10:51, 30 July 2005 (UTC)

- Jake brake seems like a popular name for an exhaust brake made by Jacobs, and could be a subset of that article. However, the jake brake article seems to describe the mechanism in clearer detail (and perhaps more correctly) by saying how the energy is dissipated by the release of the air from the cylinders.

The exhaust brake article is more extensive in mentioning the competitor of Jacobs, Pacbrake but seems confused as to the mechanism, and makes it seem the air never leaves the engine.

An air brake (rail) is very different from everything else and should remain in its own article. It mentions trucks, but refers to applying pneumatic pressure to activate regular friction braking. Also, compression brake probably is fine as a redirect. Exhaust brake/jake brake is a mechanism that does not exist in regular cars, but engine braking is possible in any car, so they are also distinct.

To remedy the number problem, I guess I'll, or someone else will come back to merge parts of exhaust brake and jake brake, hopefully maintaining all the information in the jake brake article. But Jake brake is actually an indivudual product, and merits its own article.Raazer 23:01, 23 August 2005 (UTC) -


 * Could we merge a lot of these pages together, including the section from Air brake (rail), into a new page about truck braking technology? Or maybe "large vehicle" braking systems? In some respects trucks and trains have more in common than trucks and cars. Ewlyahoocom 10:35, 4 February 2006 (UTC)


 * Agree that the section Other applications from Air brake (rail) be removed from that article; material not about railroad/railway air brakes does not belong in an article titled Air brake (rail). While I am certain that the section is out of place where it sits today, I'm not certain where the material does best belong.  Since truck braking is not an area of particular interest or expertise for me, I won't offer an opinion on this material's eventual home &mdash; those with more knowledge about that subject matter should decide.


 * I thought I'd point out that the disambiguation page for "Air Brake" lists a page (which is not created) for Air brake (commercial vehicle) which would be a good place to put all the truck-related air brake information. There is quite a bit over at Semi-trailer (now semi-trailer truck ENeville), which would be better put there, in addition to the stuff on Air brake (rail) and elsewhere. I don't think it should be moved to the Engine brake page though, since it's not really engine-brake related (it's about air brakes, which aren't engine brakes). I think there is enough stuff to have separate pages for the air braking systems of trains and trucks (and planes, and a separate page for anything else that uses them). We just need to condense all the truck stuff onto one page. There's definitely enough content, I think. -Kadin2048 02:26, 1 May 2006 (UTC)

I concur, Air brake (rail) should be just that, and not involve trucks at all.UbiquitousGeep 22:20, 15 February 2006 (UTC)


 * I will add, however, that the term Engine braking may deserve to be better qualified. There are a lot of different types of engine in the world. &mdash; JonRoma 18:59, 4 February 2006 (UTC)


 * I'll add to the mix by saying I added an article on retarders a little while ago(Retarder (mechanical engineering)), which also covers an overlapping area of this topic. I just thought I would bring it to people's attention in case a major rewrite/clean up of this topic area takes place.WLD 08:49, 15 February 2006 (UTC)

My two pence: FiggyBee 23:47, 9 June 2006 (UTC)
 * Rename air brake (aircraft) to speed brake, which as far as I'm aware is the more commonly used name.
 * Rename air brake (rail) to air brake, put a disambig link to speed brake at the top, and leave the section on trucks there. Air brakes on trucks are basically the same thing as air brakes on trains, and a completely different subject from engine braking.
 * I disagree. In my experience, "air brake" is used far more often than "speed brake" to refer to brakes on aircraft. Balfa 18:16, 11 December 2006 (UTC)

The braking effect is actually as a result of the compression stroke of the engine, both Petrol and Diesel. In fact the Diesel engine has more braking ‘power’ than the petrol because, as the wikipedia.org author states, the throttle of the petrol intake limits the air intake thus limiting the amount of air that can be compressed, and a vacuum doesn’t compress so well! Furthermore the diesel engine has much higher compression since it needs high compression for diesel ignition. (AfricaLionHeart) — Preceding unsigned comment added by AfricanLionHeart (talk • contribs) 06:01, 21 June 2011 (UTC)

question
Why are compression release engine brakes so loud? I'm also confused about whether there's combustion going on when the exhaust valve is opened at compression stroke (If anyone would care to answer). —The preceding unsigned comment was added by 71.10.233.117 (talk • contribs) 05:47, 9 September 2005.


 * I realise this answer is a bit late. In a normal engine cycle, the exhaust valve opens at the bottom of the stroke, when the gasses in the cylinder are under relatively low pressure.  The rising piston then pushes the exhaust gasses out.  However, with the compression release brake, it pops the exhaust valve at the top of the compression stroke, when the air inside is at many times normal atmospheric pressure.  This sudden release of pressurised gas is what makes all the noise - it's like  firing a gun.  The compression release brake also turns the fuel injection off (and there's no pressurised air in the cylinder any more to ignite it anyway), so no, there is no combustion. FiggyBee 23:15, 10 June 2006 (UTC)

You guys need to come over to Nairobi Kenya sometime, if you think the engine braking in your place is loud. we got commuter service mini-buses with modified exhausts that would rapture your ear drums. It sounds similar to passing all the exhaust gases from the engine through a whistle. there is no transport law governing exhausts so they try out doing each other as far as loudness is concerned. But at times there are police crackdowns on the said passenger vehicles to have the exhaust modifications removed But again, its what we like about them. Drop a line if you have any questions- +254 724394525. —Preceding unsigned comment added by 62.24.112.246 (talk) 13:01, 12 January 2008 (UTC)

Don't Merge
I don't understand why some of the Wikigeeks love to combine pages. This page is fine on it's own for several reasons:


 * Jake Brakes are a distinct item in trucking and vehicular braking
 * Jake Brake is a genericized trademark
 * The issue of compression brakes being banned on certain roads due to their noise has become a hot-button issue in many communities

I can't believe I'm actually taking the time to write my opinions on a Wikipedia article on friggin' JAKE BRAKES, but come on guys. It seems like every other article on here has some knob pushing for merging with another, semi-related article. Why not combine the articles on lard and apples, because together they make a pie? —Preceding unsigned comment added by 72.57.241.84 (talk • contribs)

"Compression Braking"
Is "compression braking" just a bad synonym for "compression release braking"? Compression release makes sense, but as the Jake Brake article tells, the compression itself is entirely countered by the spring effect in the inevitable expansion that follows, thus no net braking occurs. Balfa 18:23, 11 December 2006 (UTC)

Risks?
Are their any possible risks to the engine when breaking? For example if you use engine breaking on an steep hill, is there a point where you should use your regular breaks to prevent too much strain on the engine? amRadioHed 23:41, 10 January 2007 (UTC)
 * Actually that's a good point; May be worth adding to the article. The risk is basically that you can over-rev the engine. If you were, for instance, in 2nd gear going down a really steep hill, there is a good chance the engine braking won't be enough to stop gravity accelerating the car down the hill - The engine RPM will continue to increase until something breaks. In you're in that situation, it's important that you go up a gear and/or engage the friction brakes to slow the car down and stop the RPMs shooting up. (It'd have to be a bloody steep hill tho') 92.234.58.169 (talk) 20:56, 30 May 2014 (UTC)

Clarification
Yes. Please do clean this up. I was actually confused about the explanation. It seemed at first that all you were doing was explaining how a diesel engine works compared to a gasoline engine. I scrolled down looking for the description of the actual topic and realized you were trying to do that already. A bit confusing. —Preceding unsigned comment added by Theillien (talk • contribs) 11:40, 30 March 2007
 * I have tried to rework the design section to get to the procedure and the results of the procedure.Raazer 15:44, 7 April 2007 (UTC)

Confusion
The description could be misleading to whoever reads it. You should definitely go thru it and clarify the explanation. —Preceding unsigned comment added by Hbettis (talk • contribs) 14:34, 2 October 2007 (UTC)

fuel?
There should be information in the article regarding whether engine braking affects fuel economy. --Joy &#91;shallot&#93; (talk) 23:57, 15 December 2007 (UTC)
 * I was under the impression that injected vehicles will in fact not inject fuel when the throttle is closed and the engine is still turning. --GSchjetne (talk) 12:21, 20 May 2008 (UTC)
 * That's ridiculous. Then the engine would die every time you're at a stoplight and the foot is only on the brake. Novasource (talk) 13:17, 20 May 2008 (UTC)
 * It does indeed die if you do that - unless you have automatic transmission, where the torque converter performs the same effect as disengaging the clutch in a conventional transmission car. But this behaviour is completely unrelated to fuel injection. --GSchjetne (talk) 05:35, 30 May 2008 (UTC)
 * Fuel injection resumes once the engine speed is near the idle speed, of course. This behavior was documented in the shop manuals for my Honda Civic del Sol and my MINI Cooper S.  It's certainly not "ridiculous".  -- Coneslayer (talk) 13:55, 20 May 2008 (UTC)
 * I don't see how that would work without a direct connection between the rear wheels and the engine, and that can only happen with an automatic that is at coasting RPMs (torque converter lockup engaged) or a manual transmission. With an automatic and a disengaged torque converter clutch, the engine would immediately fall to 0 RPMs without any fuel.
 * Also, are you sure that "shut off" is literal? Could it not be euphemistic for "turned down to normal idle fuel consumption"?
 * Novasource (talk) 14:16, 20 May 2008 (UTC)
 * I'm not sure what the rear wheels have to do with anything in the cars I listed, and I'm sure that it's a full cutoff. The del Sol manual specifically indicated the engine speed at which fuel flow resumes (something like 1,000 rpm, from memory).  I don't know a lot about slushboxes, and I don't really follow your argument.  You seem to be suggesting that the engine is completely decoupled from the wheels during engine braking.  As far as I can tell, the wheels are still turning the engine.  Otherwise, what do you think is keeping the engine speed synchronized with the wheel speed?  -- Coneslayer (talk) 16:58, 20 May 2008 (UTC)
 * PS: See, for example,  (look for "Over-run fuel cut-off"), or  (search for multiple occurrences of "Overrun"). -- Coneslayer (talk) 17:10, 20 May 2008 (UTC)
 * Ah, you're correct. My bad. I was forgetting you would have to shift out of gear to cause the drop to 0 RPM, and that would apply regardless of transmission type. Novasource (talk) 18:17, 20 May 2008 (UTC)

It's good to see this information added, thanks. But, there is no explanation of what "overrun fuel shutoffs" are (or a link to an appropriate article). Does the common car made these days typically have this feature? --Joy &#91;shallot&#93; (talk) 01:27, 6 September 2008 (UTC) What about addressing the simple problem/question; when going downhill should people driving an automatic transmission downshift to 1st or 2nd gear or will they blow their transmission? —Preceding unsigned comment added by 76.242.91.183 (talk) 02:48, 13 October 2008 (UTC)
 * That would very much depend on the hill and the type of autobox; Generally it's best to let the car figure it out. If it's a really steep hill and the car is quite stupid, manually overriding it for a lower gear would be beneficial for the same reasons it is on a manual. It's worth noting that Toyota Hybrids will not engine-brake unless they are in B-mode (Normally the automatic regen-brake is enough, but as it stops working when the battery is full, B-mode can be needed on long hill descents). It's not recommended to use downshifts for engine-braking on CVTs as it can fuck up the belts, but you're usually okay with semi-autos (MMT, DSG etc.) and 'real' autoboxes (i.e. torque converters). Note there are very few circumstances you'd want to go to 1st gear unless the hill is dangerously steep; I don't think I've ever gone lower than 3rd personally except once where I got lost in Wales and had to go down a 45 degree slope (!!). That was f'ing scary lemme tell you...! 92.234.58.169 (talk) 21:07, 30 May 2014 (UTC)

Physics and Mathematics
What I am missing in the article is something about how the amount of engine break torque or power can be calculated. Maybe there could be a reference to some related article if this one is supposed to only describe the meachanics. There should be information available about how to calculate this, or at least some graphs from real life testing. Without the physics/mathematics behind the topic, I find it incomplete. —Preceding unsigned comment added by 85.227.143.102 (talk) 14:56, 27 February 2010 (UTC)

Legal implications section
This section only makes reference to legal implications in the last paragraph. The first two are irrelevant to legalities. — Preceding unsigned comment added by Abrusletten (talk • contribs) 17:44, 14 September 2013 (UTC)

Using engine braking and brakes together
Does it improve or reduce braking efficiency if using both regular brakes and engine braking at the same time?

January 2017
There are various problems associated with the idea that it is the closed throttle that creates engine braking: Conservation of energy: On a descent where if we used solely the brakes to remove the vehicles gravitational potential energy we would expect and do see very hot brakes(red hot discs) and heat emitted from the wheels etc. If it is the restriction through the throttle plate that removes/transfers the energy, we should be seeing red hot areas around the throttle intake regions.......but alas we don't, a law of physics would have to be violated for the closed throttle theory to be correct.

"Power/force" of a vacuum is often mentioned:  If the throttle was completely closed then the piston only has to overcome 15psi of outside pressure to move against the "power" of the vacuum, this is small compared to the pressure that occurs on the compression cycle where we can easily get 120-200psi(depending on revs and cam profile), this is where the serious engine braking occurs.

Also depending on the revs and profile, the more air that is sucked into the motor, the higher the dynamic compression ratio, this is why when testing the compression of an engine it must be done at WOT

Many have not tried this, but if have an old school cable throttle where one can switch fuel and/or spark off, then there will be slightly more engine braking applied if you use WOT.

The energy used in compression is returned in the power stroke, just like a spring? Well a spring with incredibly high damping factor would be more accurate! the compression is non adiabatic and the process of returning the stored energy in an internal combustion energy is well less than 20%. One only has to try turn a small engine(like on a motor mower) over by hand with open throttle and no fuel and see how quickly it stops spinning, and then compare when a spark plug is removed, the friction of the moving parts counts for little. One can also see this if you turn off a petrol engine doing say 2000rpm, it stops within a second, even if you give it WOT whilst turning it off.

So where does the energy go that would have turned the brakes red hot, it goes into heating the air within the engine when compression occurs, some getting transferred to the cylinder walls and some out the exhaust. The proof is in the pudding, go from closed throttle to WOT whilst engine braking with no fuel/spark and there will be basically small noticeable increase in braking going to WOT, rather than zero engine braking when full throttle is applied.

The article should be pulled down, I am not the first person to make these points and so far the original author has not made any attempt to address these issues. In regard to the references cited, they are wrong, being published simply does not make them correct, and wiki is simply just perpetuating the myth of those publications. I have a citation that is more powerful, the conservation of energy law, which is violated by the closed throttle idea, here is a reference: https://en.wikipedia.org/wiki/Conservation_of_energy  Sacspeed (talk) 03:19, 21 January 2017 (UTC)Sacspeed (talk) 03:03, 21 January 2017 (UTC) Sacspeed (talk) 21:54, 19 January 2017 (UTC)


 * The thing to understand is that Wikipedia articles should contain no original research (please click & read). Improving this article should consist of finding reliable sources, and citing them. The article should reflect whatever the sources say, nothing more. When you start reading the published experts (here's a couple examples, they all say closing the throttle increases engine braking. If you wanted the article to say anything that contradicts this, you would need to find and cite reliable sources (read Identifying reliable sources) which state this opposite position.Your arguments might serve as a motivation for editors to carry out further research into the sources to see if there is a controversy or disagreement among published experts on engine braking, but that's all unsourced opinions can do. Editor opinions are not "proof" of anything. You can believe it, but it's not relevant to article editing until there's sources to go with it.By all means, if you know of a published source that says it, then do cite it in the article, or identify the source here so other editors can make use of it. --Dennis Bratland (talk) 01:33, 20 January 2017 (UTC)