# Devices that claim to improve gas mileage **URL:** \ **Category:** Factual Questions\ **Created:** [August 27, 2007, 5:26pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120 "2007-08-27T17:26:31Z")\ **Posts on this page:** 15\ **Page:** 3
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [September 1, 2007, 10:54pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/41 "2007-09-01T22:54:48Z")
Hmmm. Here’s another anecdote found on the web: “One of my big rig drivers is claiming he’s seeing a 1 mpg increase OTR (500 Cat). I’m always willing to give anything a try, but it’s a limited availability (only a few retailers) or mail order only. The price is steep, but when computing out recommended ratios seems no more expensive than other additives. It appears that this additive is purely for a mileage boost, and does nothing for gelling or water.” Right now I’m personally sold on Fuel Power 3000. It claims small improvements, but it did perform in tests by the Southwest Research Institute. ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [September 1, 2007, 11:35pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/42 "2007-09-01T23:35:00Z")
[QUOTE=ralph124c] I’m intrigued by the possibility of using the waste heat from the IC engine, to power a smaller staem engine-would this make sense? Suppose your steam engine could recover 30% of the waste heat-that would mean an overall increas of about 20%-would that be worth it? There is one other possibility-ultra-low viscosity oils-do they make any significant difference? [/QUOTE] I have seen reports of an developer who has working on a 6-cycle engine. Added to the normal intake-compression-combustion-exhaust cycle are a water injection and steam expansion cycle. The claim was 20% more fuel economy. This idea has been kicking around for a while, and why not? As you correctly note, there’s a lot of waste heat in an IC engine. ---
**Author:** ![Cranky\_Old\_Man](https://avatars.discourse-cdn.com/v4/letter/c/e19b73/32.png) [@Cranky\_Old\_Man](https://boards.straightdope.com/u/Cranky_Old_Man)\ **Post date:** [September 2, 2007, 12:44am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/43 "2007-09-02T00:44:31Z")
Water injection schemes have been around as long as I can remember. It’s not new. How could a small magnet possibly effect gasoline? ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 2, 2007, 1:21am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/44 "2007-09-02T01:21:44Z")
[QUOTE=Cranky Old Man] How could a small magnet possibly effect gasoline? [/QUOTE] It ionizes its paramagnetic resonances to amplify the hydrodynamic turbulence resulting in increased plasmatic radiative output. Duh! Stranger ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [September 2, 2007, 1:22am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/45 "2007-09-02T01:22:28Z")
[QUOTE=Digital Stimulus] I’m glad this thread is open right now. I just got off the phone with my SIL, who mentioned [CA-40](http://www.ca40g.com/) to me (she said she heard about it via Ed Shultz from NPR, where it was getting heavy endorsements). I’d never heard of it before, and am approaching it with some skepticism; however, I’m going to look into it (in addition to following the links presented thus far in this thread). Does anyone have any knowledge of this product? (An SDMB search turned up nothing.) [/QUOTE] From their website: > [@](#): > > Usually only about half of the hydrocarbons in fuel are burned in an internal combustion engine. What the holy fuck? Half of your gasoline heads out the exhaust as unburned CO? OK…let’s think about this logically. And let’s set the wayback machine to an era when Cadillacs had tailfins, stockings had seams (rrrrrrow!), and America had promise. From: [http://epa.gov/otaq/consumer/12-miles.pdf](http://epa.gov/otaq/consumer/12-miles.pdf) > [@](#): > > Air pollution and cars were first linked in the early 1950’s by a California > researcher who determined that traffic was to blame for the smoggy skies over > Los Angeles. At the time, typical new cars were emitting nearly 13 grams per > mile hydrocarbons (HC), 3.6 grams per mile nitrogen oxides (NOx), and 87 > grams per mile carbon monoxide (CO). OK…let’s say a car would get about 15 miles per gallon back then. This means that every mile, about 7 lbm/15 = 0.466 lbm of fuel would be burned. Roughly - hey, bear with me, I ain’t getting paid for this. OK…that’s 211.67 grams of gasoline burned per mile. If a car typically produced 13 grams of unburned hydrocarbons, then that’s a combustion efficiency of 93.8%. Now since these are unburned hydrocarabons, the air weight does not enter into it. It does for the CO, but remember, CO is partially combusted - you just don’t get the same energy as a complete C + O2 -\> CO2 reaction. But hell, let’s assume all that CO yields no energy. So let’s remove the oxygen mass by the ratio of the weight of C/CO, and that’s another 87\*(12/28) = 37.29 grams per mile of carbon. So let’s say a total of 50.29 grams of unburned hydrocarbons per 211.67 grams of gasoline burned. That gets close to only 77% combustion efficiency. Yes, cars sucked back then. But now let’s go forward to 1970, when Corvettes were cool, hippie chicks were open to all sorts of “free lesbian love”, and we were stuck in a war far overseas for a cause no one really believed in anymore. Here we see that: > [@](#): > > 1970 Congress adopts the first major Clean Air Act, establishes the U.S. > Environmental Protection Agency (EPA), and gives the new Agency broad > responsibility for regulating motor vehicle pollution. The clean air law > calls for 90 percent reductions in automotive emissions. New cars must > meet a 0.41 gram per mile HC standard and a 3.4 grams per mile CO > standard by 1975; NOx emissions must be reduced to 0.4 gram per mile by > 1976\*. Now, you may say that “catalysts could be responsible for all that”, and it’s true that they would be in many cases, but not all I owned not one but 4 cars made after 1975 which had no catalyst, because they met the emissions limits. Including one 1979 car, the last year before catalysts were mandatory (IIRC) regardless. How efficient did combustion have to be for those cars? Well, my Honda Civic got about 35 mpg city at that time - so we can say that’s (7/35) .2 lbm of gasoline per mile. Or about 90.7 grams of gasoline per mile. Now, 0.41 grams per mile HC, plus [3.4(12/28) = 1.45] 1.45 grams per mile CO (again, assuming NO energy from the CO creation) yields about 1.86 grams of unburned hydrocarbons per mile. Overall, about 1.86/90.7 = 97.9% combustion efficiency. I can imagine that modern fuel-injected engines get better than that now, but I don’t have figures handy. Another data point I grabbed quickly gives these relations: > **[EPA Testing Methods](https://www.allpar.com/threads/epa-testing-methods.236662/?post_id=1085245075&nested_view=1#post-1085245075)** > > EPA Testing Methods > > EPA gas mileage standards were originally developed based on a mid-1960s project where surveyors were sent to all major United States cities to discover the conditions of a typical commute. Traffic was much lighter at that time,... > [@](#): > > ## Non-Catalyst Emissions at A/F = 14.7 > > ## HC output is approximately 17 grams/gallon CO output is approximately 383 grams/gallon NOx output is approximately 66 grams/gallon Total emissions about 466 grams/gallon Post-Catalyst (3-way) Emissions for A/F = 14.7 > > HC output is approximately 1 grams/gallon > CO output is approximately 62 grams/gallon > NOx output is approximately 5 grams/gallon > Total emissions about 68 grams/gallon For a 30 mpg car (105.8 grams/mile gasoline), the above emissions would be: HC: 17/30 = 0.57 gram per mile. CO: (12/28)\*(383/30) = 5.47 gram per mile. NOx - N/A Total unburned hydrocarbons: 6.04 gram/mile Combustion efficiency: ((105.8-6.04)/105.8) = 94.3% I may have got some numbers slightly wrong, but generally speaking, I think we see that the claim of “Usually only about half of the hydrocarbons in fuel are burned in an internal combustion engine.” is quite…strange. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 2, 2007, 1:41am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/46 "2007-09-02T01:41:54Z")
[QUOTE=ralph124c] I’ll telly you how: increase the air pressure in your tires by 10%. This will give a harder ride, but should be OK. Next, drive with a light foot on the accelerator pedal. Third, if stuck in traffic, shut your engine off. Idling for more than 1 minute used more gas than retarting. All of this costs nothing! [/QUOTE] Suggestion #2 is good, but #1 is suspect at best (running that higher than recommended pressure will give degraded roadholding performance and increased tread wear) and #3, while nominally more or less true is misguided. It’s true that you’ll burn more gas in idling for more than ~90 seconds than you will by starting the engine; however, by shutting off the engine the fluid layer of pressurized oil which keeps the crankshaft from contacting the bearings while rotating disappears and you get bearing wear in the engine, as well as increased use of the engine starter, reducing life. (Admittedly, this is much less a concern with modern cars running higher oil pressure than older ones, but such contact still occurs.) It’s also unsafe to turn off your engine in the middle of the road and serves to delay traffic when it does start moving. If you plan on being in the same position for more than a few minutes then it’s wise to turn off the engine, but if you’re in stop and go traffic the best thing you can do for your car and yourself is get out of it and take an alternative route if possible. **Una Persson** , I don’t have either my _Internal Combustion Engine Fundamentals_ or _Mark’s Standard Handbook_ here at home but those numbers look about right to me. The notion that you’re leaving half of the fuel unburnt is absurd. Stranger ---
**Author:** ![Merkwurdigliebe](https://avatars.discourse-cdn.com/v4/letter/m/74df32/32.png) [@Merkwurdigliebe](https://boards.straightdope.com/u/Merkwurdigliebe)\ **Post date:** [September 2, 2007, 1:58am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/47 "2007-09-02T01:58:33Z")
It’s hilarious how Americans react to higher gas prices. Well it’s getting expensive…Maybe I should sell the SUV and buy a small car? BUT WAIT! I could get the best of both worlds with the new GAS MAGNET! Europeans have switched to proven gas-saving technologies as a result of high gas prices. Everyone over there drives diesels and manual transmissions. So do I and my car can get no lower than 40 MPG ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [September 2, 2007, 2:11am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/48 "2007-09-02T02:11:15Z")
[QUOTE=Merkwurdigliebe] It’s hilarious how Americans react to higher gas prices. [/QUOTE] It has nothing to do with Americans and high gas prices. Fuel-line magnets and other chimerical gas savers have been popular ways to bilk people of their money for a very long time. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 2, 2007, 4:18am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/49 "2007-09-02T04:18:38Z")
[QUOTE=Stranger On A Train] It ionizes its paramagnetic resonances to amplify the hydrodynamic turbulence resulting in increased plasmatic radiative output. Duh! Stranger [/QUOTE] 8/10. You would have got 9/10 if you’d used the word “harmonic”. ---
**Author:** ![Digital\_Stimulus](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Digital\_Stimulus](https://boards.straightdope.com/u/Digital_Stimulus)\ **Post date:** [September 2, 2007, 3:38pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/50 "2007-09-02T15:38:08Z")
Thanks all for the info. After I posted, I got caught up in Saturday chores; however, bedtime reading consisted of following up on this. Looking at the CA40 “How it works” page (which appears bogus if one actually tries to understand it) inspired some late night googling and wikipedia reading. ( **Una Persson** , thanks for the numbers; I was trying to find something comparable, but got sidetracked by this [“automotive gasoline FAQ”](http://www.turborick.com/gsxr1127/gasoline.html).) Interesting, but I have some technical questions – I’d like to understand combustion and its related chemistry a little better and, more to the point, what is wrong with the CA40 “explanations” so that I can explain it to someone else later. I note that a bunch of the following (but not all) fall in the realm of “WTF is this nonsense?” 🙂 [ul] [li]What does the unit “lbm” stand for (as in “This means that every mile, about 7 lbm/15 = 0.466 lbm of fuel would be burned.”)?[/li][li]Is it at all possible (not likely, I understand) that their claim about “half of hydrocarbons in fuel are burned” has some non-standard reference? What I mean is, it boggles my mind that they’d cite such a blatant falsehood; acknowledging my own ignorance, I have to at least admit the possibility that the obvious explanation (it’s bullshit) isn’t justified.[/li][li]They say that “When CA-40 is added to fuel the calcium bonds to hydrocarbons within the fuel”. What? If it _were_ to “bond”, wouldn’t it be an exothermic reaction? (That is, the chemical bonds would only take place if a more stable molecule were to form, which would require breaking existing bonds and releasing energy.) I’d think this would be a **bad thing** to have going on in one’s gas tank.[/li][li]They claim that the calcium causes a “more efficient burn of the fuel” – what is it about the molecular structure of fuel that makes one type burn more efficiently than another? (From the FAQ I linked above, I’m guessing one thing might be simple chains of carbon/hydrogen atoms, with few “rings”. Another would be the phase change temperature properties of different fuels.) Is there _any_ reason that the addition of calcium would “increase burn efficiency”?[/li][li]Is there any role of “thermoelectricity” and/or “piezoelectricity” in combustion? More generally, I suppose, does electricity (at least, in common parlance) have anything to do with combustion (beyond the initial spark)? I was under the impression that it was the energy of the heat produced by the initial explosion that caused the rest of the burn (I think it’s called the “burn front”). Is that correct?[/li][li]By “longer, stronger push during combustion”, I took it to mean that “longer” referred to the length of time over which combustion was taking place. I’m not sure what “stronger” might mean here: A greater volume of post-burn gas? A higher temperature of burning? Something else? Either way, it seems to me that the two are in opposition; a “longer” burn would necessarily result in a weaker explosion. Do I have that right?[/li][/ul] I think I might have to pick up that Moran book at some point for recreational reading…thanks for that recommendation, **Stranger**. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 2, 2007, 4:59pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/51 "2007-09-02T16:59:21Z")
[QUOTE=Digital Stimulus] [ul][li]What does the unit “lbm” stand for (as in “This means that every mile, about 7 lbm/15 = 0.466 lbm of fuel would be burned.”)?[/ul][/li][/quote] Pound-mass, as opposed to the more commonly used pound-force. lbm is technically part of the foot-poundal-second system (where a poundal is a unit of force scaled to the pound-mass) rather than the more common foot-pound-second system (where pounds are a unit of force and slugs are the unit of mass). In practice, non-technical people (and even a large number of engineers) tend to use pound-force and pound-mass together, and (hopefully remember to) throw in the 32.2 ft/s[sup]2[/sup] conversion factor where appropriate. [QUOTE=Digital Stimulus] [ul][li]Is it at all possible (not likely, I understand) that their claim about “half of hydrocarbons in fuel are burned” has some non-standard reference? What I mean is, it boggles my mind that they’d cite such a blatant falsehood; acknowledging my own ignorance, I have to at least admit the possibility that the obvious explanation (it’s bullshit) isn’t justified.[/ul][/li][/quote] It’s just complete nonsense, as **Una Persson** ’s calculation demonstrates. I’m sure there’s some kind of technical loophole they can cite–for instance, when ignition is just starting, or the intake manifold is cold, or whatever–but if you were kicking out that much unburned fuel and the corresponding amount of unused oxygen the exhaust management system of a modern car would be going crazy with warnings. [QUOTE=Digital Stimulus] [ul][li]They say that “When CA-40 is added to fuel the calcium bonds to hydrocarbons within the fuel”. What? If it _were_ to “bond”, wouldn’t it be an exothermic reaction? (That is, the chemical bonds would only take place if a more stable molecule were to form, which would require breaking existing bonds and releasing energy.) I’d think this would be a **bad thing** to have going on in one’s gas tank.[/ul][/li][/quote] Yeah, it’s total crap. I suppose there might be some kind of weak, low energy hydrogen bonding going on between their additive and the fuel in the tank, but it can’t be much before going to equilibrium. This is just an example of craptastical use of jargon. [QUOTE=Digital Stimulus] [ul][li]They claim that the calcium causes a “more efficient burn of the fuel” – what is it about the molecular structure of fuel that makes one type burn more efficiently than another? (From the FAQ I linked above, I’m guessing one thing might be simple chains of carbon/hydrogen atoms, with few “rings”. Another would be the phase change temperature properties of different fuels.) Is there _any_ reason that the addition of calcium would “increase burn efficiency”?[/ul][/li][/quote] I’m not a combustion chemist so I can’t offer a definitive answer to the question, but if it did so by any normal process people, and particularly the automotive industry which is constantly being pushed for higher efficiency and complete combustion would be all over it. [QUOTE=Digital Stimulus] [ul][li]Is there any role of “thermoelectricity” and/or “piezoelectricity” in combustion? More generally, I suppose, does electricity (at least, in common parlance) have anything to do with combustion (beyond the initial spark)? I was under the impression that it was the energy of the heat produced by the initial explosion that caused the rest of the burn (I think it’s called the “burn front”). Is that correct?[/ul][/li][/quote] Technically I suppose you could apply the term “thermoelectricity” to any chemical reaction as they involve the exchange or breaking of electronic bonds. In practice, thermoelectricity is use to refer to the class of phenomena that result in a measurable electical potential that occurs due to a chemical or solid state reaction, such as what happens in an electic battery or the Peltier Effect used in thermocouples. Piezoelectricity is the generation of electricity via an imposed deformation and resultant stress on a crystaline or polymer matrix, and are used in pressure sensors, microphones, small actuators, and other devices that convert stress or pressure into electricity. I have never heard of a fluid demonstrating piezoelectric property and lacking, as it does by definition, a structure, I don’t see how it could. I call a totally bullshititudinous use of technobabble here. [QUOTE=Digital Stimulus] [ul][li]By “longer, stronger push during combustion”, I took it to mean that “longer” referred to the length of time over which combustion was taking place. I’m not sure what “stronger” might mean here: A greater volume of post-burn gas? A higher temperature of burning? Something else? Either way, it seems to me that the two are in opposition; a “longer” burn would necessarily result in a weaker explosion. Do I have that right?[/ul][/li][/quote] Combustion occurs all through the power stroke and tails off on into the exhaust stroke. Power output from combustion is complicated, as the gas expands it cools, so if you can continue combustion during expansion you’ll get more energy. In fact, a major push in engine design over the last twenty-five years is to get better fuel-air mixing and more complete combustion (hence, multiple intake and exhaust valves, hemispherical or swirled combustion chambers, turbocharging, supercharging, MillerCycle-type supercompression, variable valve timing, et cetera). However, the fuel is what it is. The additive is either a more energy-rich substance than the gasoline (and thus changes its properties) or the whole claim is nonsense. [QUOTE=Digital Stimulus] [list]I think I might have to pick up that Moran book at some point for recreational reading…thanks for that recommendation, **Stranger**. [/QUOTE] Warning: Moran and Shapiro is not light reading; it’s a college level textbook on engineering thermodynamics, and I don’t think it has much if anything to say on internal combustion engines beyond a theoretical discussion regarding the Otto and Diesel cycles. You’re probably better off with something like _Internal Combustion Engine Fundamentals_ or the _Bosch Automotive Handbook_ if you want to know about applied thermodynamics with respect to automotive engines. Stranger ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [September 3, 2007, 2:13am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/52 "2007-09-03T02:13:52Z")
**Stranger** answered your questions fairly well, I see. [QUOTE=Digital Stimulus] [li]What does the unit “lbm” stand for (as in “This means that every mile, about 7 lbm/15 = 0.466 lbm of fuel would be burned.”)?[/li][/QUOTE] As Stranger said, on this planet assume lbm = pound for practical purposes. I had professors in school who brutally drilled lbm and lbf into us as the “proper” ways to refer to mass and force in the US system. [Quote] [li]Is it at all possible (not likely, I understand) that their claim about “half of hydrocarbons in fuel are burned” has some non-standard reference? What I mean is, it boggles my mind that they’d cite such a blatant falsehood; acknowledging my own ignorance, I have to at least admit the possibility that the obvious explanation (it’s bullshit) isn’t justified.[/li][/QUOTE] Oddly, I spent some serious time Googling for “internal combustion engine efficiency” and other terms last night, and came up with very, very few references. In fact, if I had been able to find authoritative cites which were online, I wouldn’t have done any math. Having had multiple graduate courses on internal combustion engines, I knew I could do some quick math and show that something on the order of “half are unburned” was clearly false. However, it’s very possible that the average person really does think, or would easily believe, that half their gasoline isn’t burned. Remember, the average American, I’ll wager, _has no clue at all_ about how an internal combustion engine actually works. [QUOTE] [li]They say that “When CA-40 is added to fuel the calcium bonds to hydrocarbons within the fuel”. What? If it _were_ to “bond”, wouldn’t it be an exothermic reaction? (That is, the chemical bonds would only take place if a more stable molecule were to form, which would require breaking existing bonds and releasing energy.) I’d think this would be a **bad thing** to have going on in one’s gas tank.[/li][/QUOTE] It sounds like flim-flam bullshit to me. [QUOTE] [li]They claim that the calcium causes a “more efficient burn of the fuel” – what is it about the molecular structure of fuel that makes one type burn more efficiently than another? (From the FAQ I linked above, I’m guessing one thing might be simple chains of carbon/hydrogen atoms, with few “rings”. Another would be the phase change temperature properties of different fuels.) Is there _any_ reason that the addition of calcium would “increase burn efficiency”?[/li][/QUOTE] Well, it’s true that engines aren’t 100% efficient, and so claims can always be made that _something_ could increase combustion efficiency. It’s possible that some chemical, some catalyst, some process could increase combustion efficiency by a partial fraction of a percent. But at what cost? And with what other drawbacks? [QUOTE] [li]Is there any role of “thermoelectricity” and/or “piezoelectricity” in combustion? More generally, I suppose, does electricity (at least, in common parlance) have anything to do with combustion (beyond the initial spark)? I was under the impression that it was the energy of the heat produced by the initial explosion that caused the rest of the burn (I think it’s called the “burn front”). Is that correct?[/li][/QUOTE] If I understand you, then generally speaking the single spark is all that’s needed. However, multiple spark engines have been known and even appeared in production cars, and the benefits have typically not been worth the extra effort. In race cars, especially large displacement engines, I believe that multiple spark plug cylinders are used effectively. [QUOTE] [li]By “longer, stronger push during combustion”, I took it to mean that “longer” referred to the length of time over which combustion was taking place. I’m not sure what “stronger” might mean here: A greater volume of post-burn gas? A higher temperature of burning? Something else? Either way, it seems to me that the two are in opposition; a “longer” burn would necessarily result in a weaker explosion. Do I have that right?[/li][/QUOTE] I think the concept you’re looking for here is brake mean effective pressure, or bmep. And it gets quite complicated to explain, but generally speaking things which increase the mean effective pressure (forcing down on the piston) over the expansion cycle of the piston result in increasing the torque of the engine. Since power is torque times rpm over a constant, it then can increase the power of the engine. > [@](#): > > I think I might have to pick up that Moran book at some point for recreational reading…thanks for that recommendation, **Stranger**. I recommend the books **Stranger** recommended. I have both of them sitting right here beside me, in fact. ---
**Author:** ![Emilio\_Lizardo](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@Emilio\_Lizardo](https://boards.straightdope.com/u/Emilio_Lizardo)\ **Post date:** [September 5, 2007, 1:29pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/53 "2007-09-05T13:29:31Z")
[QUOTE=Stranger On A Train] the thermodynamic efficiency of the Otto Cycle (or similar four stroke cycles which drive most gasoline-fueled engines) is limited by the difference in temperature between the temperature of injected fuel and air and the combustion temperature of gasoline. [/QUOTE] Does this mean that a device to warm the fuel-air mixture before it is injected into the cylinder might improve mileage? ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 5, 2007, 2:55pm UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/54 "2007-09-05T14:55:47Z")
[QUOTE=Emilio Lizardo] Does this mean that a device to warm the fuel-air mixture before it is injected into the cylinder might improve mileage? [/QUOTE] Probably not. The compression stroke of the engine heats the air fuel mixture in the cylinder to just under the auto ignition temperature of the mixture. If you pre-heated the mixture, then during the compression stroke it would ignite spontaneously, causing emissions to go up and power to go down. Many cars do have a TAC (thermostatically controlled air cleaner) that does pre-heat the air on cold engines to stabilize the idle, and lower the emissions during cold start and warm up. If the thermostat in the TAC fails, and hot air is directed to a warm engine both emissions and power are affected negatively. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 6, 2007, 12:31am UTC](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120/55 "2007-09-06T00:31:44Z")
[QUOTE=Emilio Lizardo] Does this mean that a device to warm the fuel-air mixture before it is injected into the cylinder might improve mileage? [/QUOTE] You have it backwards. The greater the difference the greater the ability to do work. If you heat the mixture before it goes in, you have _less_ of a useful temperature difference. Plus the energy you would use to warm the mixture would have to come from somewhere. [Previous page](https://boards.straightdope.com/t/devices-that-claim-to-improve-gas-mileage/417120.md?page=2)