The Best Way To Compare Engine Efficiency - BSFC
Brake Specific Fuel Consumption - How Massive Engines Can Be Efficient
Comparing Engine Performance: BMEP -
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Brake Specific Fuel Consumption (BSFC) is a great way to compare the efficiency of engines. It's often referred to in units of g/kWh, (for example: 200 g/kWh) and represents the amount of fuel flowing into the engine versus how much power the engine actually makes. BSFC is directly correlated to the efficiency of an engine. The lower the BSFC, the more efficient an engine is.

In this video we'll define brake specific fuel consumption, show how it correlates with efficiency, look at a BSFC map, compare BSFC with RPM, air-fuel ratio, and engine size, and talk about ways of optimizing BSFC. We'll also look at how you can analyze the BSFC of your car engine if you have an MPG readout. This is helpful in determining what the best gear to be in for maximum efficiency.

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  • Engineering Explained
    Engineering Explained

    BSFC also helps explain why cylinder deactivation is a thing! For example, a V8 going down to four cylinders means those four cylinders have to make more power per cylinder versus eight cylinders. That puts them at a higher load, which is more efficient, and thus fuel economy improves during cylinder deactivation! If you haven't yet, I'd also recommend learning about BMEP, which is another great way to compare engines:

    • 看海人

      @Asakha A. Wolf Do not know if it is more efficient. It does have good low rpm torque. Maximum torque is achieved at 1400 rpm. If you are lazy driver like me, I like high low end torque.

    • Matt Dunlap
      Matt Dunlap

      This method does not work because it doesn’t include the btu content of the fuel per weight. This method only works to compare the engines using the same fuel. Because I could make all road Diesel engines about 10% more efficient by switching them to bunker fuel because similar mass but bunker fuel is about 10% more energy dense. Also should note that diesel and bunker fuel pollute like crazy as fuel because less refined it tends to have more btu per unit but is also much dirtier in emissions of really nasty things like sulfur dioxide

    • Matt Dunlap
      Matt Dunlap

      @Михалыч Наливай I don’t see how they are more efficient as the fuel has 20% more btu per the same weight in gas so it would need to produce 20% more work from the same weight in fuel just to match the gas efficiency.

    • Brian K
      Brian K

      @A Balakrishnan lower surface area per volume

    • Cracked Emerald
      Cracked Emerald

      I wonder if you could pipe the air pumped by the deactivated pistons into the active ones.

  • Carlos Henrique Pfiffer
    Carlos Henrique Pfiffer

    I would like to hear your thoughts about the mercedes F1 engine and their 50% efficiency engine !

  • Md Nazmus Sakib
    Md Nazmus Sakib

    Also thanks to Pulkrabek!

  • Jason Parry
    Jason Parry

    not your best video- was hoping you would compare the Bsfc of various production engines from different manufacturers

  • Petros Drakoulis
    Petros Drakoulis

    Jason, is there any way, by calculating something on the dyno graph, to find the exact maximum efficiency rpm spot?

  • Aleksi Joensuu
    Aleksi Joensuu

    Of course, engine efficiency is not equal to transport efficiency: If you're only using your semi truck which you could somehow get to make 20MPG, to only transport one person and no cargo, then of course it would be much more efficient to use that moped that gets 30MPG. I suppose most people don't, obviously, use semi trucks for personal transport, but there is a point here: If you're regularly driving a 5 person passenger car alone - then you're not being too efficient. :) How much power per unit of fuel also isn't the only thing that matters if you're purely interested in going fast: consider, say, a 70hp motorcycle in comparison with a 200hp car - you might have a fair amount quicker acceleration times for the fuel you're using.

  • J H
    J H

    Friction losses are also proportional to surface area, so same effect as heat losses.

  • Helmut Girod
    Helmut Girod

    Miles? Gallons? wie wärs mit Kilometer und Liter?

  • Matt Dunlap
    Matt Dunlap

    @EE you compare gas efficiency of marine diesel that runs bunker fuel that has 153k btu to gas motor efficiency that burns 125k btu per gallon. But both weigh 6lbs a gallon but have a massive energy density disparity. If you are using weight of fuel to determine efficiency the marine diesel would need to be over 20% more efficient to match the efficiency of a gas motor because it’s starting with 20% more energy in the fuel of my logic is correct. Am I missing something?

  • geomtol

    Excellent video! For 'loose' engines, such as marine and industrial engines the EPA has specific test cycles, typically with 4 to 5 modes with different rpm and torque, and weighting for each mode. The weighted BSFC over these cycles is an excellent way of comparing engine efficiency. It is more realistic than just looking at the best BSFC. I believe the EPA also has a somewhat similar but more complicated fuel economy driving cycle for cars, it would be interesting to see the BSFC over those cycles, but don't think those figures are typically published.

  • oldretireddude

    Thanks for the video. I have an additional MPG topic that I would like to see someone tackle and that is FIbill automotive journalists that do independent MPG tests but based on a single drive and very small amount of fuel usage. I've found that the variations in fuel pump delivery make small fuel fill-ups extremely unreliable. I would like to see someone break down the tolerances in these systems and their influences on resultant MPG numbers. Maybe provide data on a best practice for doing independent MPG calculations.

  • PotassiumShard

    You heard him guys, we need cars with marine engines

  • schwaze neggro
    schwaze neggro

    I really like it when the Man incorporates F1 in his videos as the ideal specimen😉💯

  • Mr Ed
    Mr Ed

    I know not everyone is great at driving manual transmission cars but this is where they can be better than automatic transmissions as most will not hold the gear when they should to be efficient wither it’s an up shift or down shift. I am sure it’s not that way in a perfect lab but the real world is far from a perfect setup


    please tell me im not the only person who doesnt understand horseshit here


    ive given up

  • Hadi Mezher
    Hadi Mezher

    This channel is amazing i am a second year mechanical engineering student and your channel is helping me a lot !!!!

    • Engineering Explained
      Engineering Explained

      Happy to hear it, thanks for watching!

  • Sean McNamara
    Sean McNamara

    BSFC is only half the data though, even still. You have to look at the whole vehicle. One car could be much heavier than another car while having roughly the same carrying capacity and use case. In this situation, if the heavier car's engine consumes more fuel to get from point A to point B (i.e., lower MPG), it is a worse investment if your goal is to minimize fuel consumption, even if it is technically more efficient. Basically if you factor in weight along with BSFC, then you have a pretty good measurement. Sometimes it can paradoxically save more fuel to go with a lighter vehicle with worse efficiency, if it can get you from point A to B with less fuel. Of course, you might lose out on performance, but that isn't a factor for most road vehicles, they are plenty fast enough as-is.

  • jad sabra
    jad sabra

    At 7:40 correction of "Lean" is when you have too much air and you are burning too little fuel.

  • Aaron g
    Aaron g

    So how would you calculate this yourself? Run 6 or 7 dyno runs at different throttle positions and measure fuel consumption during each run?

  • Abel Alonso Ballón Aguirre
    Abel Alonso Ballón Aguirre

    can I calculate fuel consumption with BSFC? thanks a lot! good video!

  • Gert van den Berg
    Gert van den Berg

    It would be interesting to see if fuel injection vs carburettor changes this and how... (You might be able to keep the throttle wider open at low loads, reducing pumping losses....) (Non-petrol engines might also be interesting to see... (I assume things like the lack of a throttle might be one reason why direct-injection diesels end up more efficient))

  • Slays Media
    Slays Media

    What about a comparison video showing the mechanical limitations of one engine versus another. For example, why would one 5.0 dohc v8 be more powerful than another? I get that bore to stroke ratios, piston to rod ratios, head design, and compression all play roles, but is that really enough for one engine to make 50-100 more horsepower over another without increasing displacement?

  • Dragan Crnogorac
    Dragan Crnogorac

    O nooo!!! It's not important how far away you can be with 4 liter of fuel !?!? here I have white board and I'm gonna explain it in 20 minutes... Gotta love this dude

  • Ibrahim Qari
    Ibrahim Qari

    Thanks. Heavy stuff

  • francisco saavedra
    francisco saavedra

    Janson, I haven't watched your videos for while. It's so good that you stoped using imperial system!

  • prosaic.

    I have a question. Suppose we have a hybrid car, so it has two engines that change the power output and thus BSFC. Now, *when we plug in the dyno, doesn't that calculate power by simultaneously measuring torque and rotational speed? So, isn't because electric motor changes the power output, BSFC is NOT the efficiency of the combustion engine, but the efficiency of the powertrain?* As power of the combustion engine can be read differently by changing the electric motor.

  • kartdude2006

    Great video, next one should be on BMEP 👍👍

  • Russ Huston
    Russ Huston

    I have wondered...given the speed with which gasoline burns ( I suspect that's a variable value, with different degrees of compression and completeness of atomization-vaporization of the fuel ) is there an approximate ideal volume of a cylinder? I've heard some say 500 CC's is about right, but I don't know if that's correct. 2 litre for a 4 cyl, 3 litre for a 6, and so on. Is there an answer?

  • Dan Ellerbe
    Dan Ellerbe

    Awesome explanation!

  • Steve Sedio
    Steve Sedio

    Nicely done. The maximum burn temperature is when all the fuel is consumed, and there is no oxygen left over. That provide the highest cylinder pressure (primarily from heat, 28% is from converting gasoline to water and CO2). Too rich, you are evaporating and heating fuel that isn't burned. Too lean and you are heating oxygen (and 4 times as much nitrogen) that isn't used for combustion. Lower cylinder temp, less pressure, less torque. Adding fuel at high power is to avoid detonation by cooling.

  • Mario Sanchez
    Mario Sanchez

    Could you breakdown how a modified turbocharged vehicle could be as efficient as a stock vehicle. Coming from efficiency standpoint and nox emissions

  • KitMellow

    So what you're saying is MPG is still the best way to compare engine efficiency, so long as you're talking about the same class of vehicle.

  • zookeroni


  • Christoffer Ceutz
    Christoffer Ceutz

    It should be possible to have this plot available on the car dash in modern cars. Maybe something is possible with an App and an OBD2 adapter...

  • Sasa Jungic
    Sasa Jungic

    No wonder why small turbocharged engines suck in real world conditions

    • Sasa Jungic
      Sasa Jungic

      @Zuurker U yeah that’s the thing. I could also achieve some good fuel consumption but at 70-80 mph on the motorway at a steady speed it was really bad. It was a Toyota CHR with a 1.2 turbo btw

    • Zuurker U
      Zuurker U

      They are efficient, if your "real world" happend to be a professional hyper miler xD I actually beat the rated consumption in My Volvo v40 t2

  • Wingnut353

    A potential problem with BSFC is that it does not consider the volume or weight of the engine... as such a big giant engine that is very efficient would appear to perform better than a small engine. While in practice the small engine may perform better in practice due to being lighter.

  • GameOverVirus

    This doesn’t just help with efficiency, it also goes a great way to figuring out how powerful your engine actually is by literally calculating how much power you are making with a single unit of fuel. Which is great because one thing that I don’t like about horsepower and torque is that it doesn’t actually tell you much of anything. Some of the fastest hypercars around can breach 300 mph with only a couple hundred horsepower, whilst there are custom cars that go way over a 1000 horsepower and they only get to about mid 200 mph. BSFC allows us to know how much power that engine is actually making, and how much of it is actually be used.

  • twowheeler1000

    Aren't smaller engines more efficient at higher rpm's? I have a car with a 1.4l engine and it's at rougly 3800rpm at 120kmh. The engine feels really smooth there and not taxed. Running that engine at the same speed but with 2000rpm would mean it had to be at full throttle to be even able to hold the speed. That engine would be really taxed at that engine speed. A 2l engine with more power can handle that rpm easily though.

  • Michael Theos
    Michael Theos

    Someone once told me that, because engines are most efficient at max torque, the most efficient way to drive is to accelerate at high throttle until (you reach cruising speed or) the torque at the wheels of your current gear is less than the torque of the next gear and then shift gears. That made sense to me then and I think this is the theory that explains it.

  • Joe K
    Joe K

    ................. So how do I sell this to the SO on getting a 632ci crate engine for my the RF Miata I want?

  • Nick McGarvey
    Nick McGarvey

    I love these math and data heavy episodes. Truly explaining engineering.

  • DC

    Uh, wait a minute ... BSFC of course is the best way to compare efficiency - but ... but the deviance from the sweetspot isn't the same every time. The actual stuff causing it is similar, of course, but ... more interesting than the peak efficiency, at least to me, is how well it matches the map of engine use (which requires a given driving cycle to be comparable). Which is the entire point of downsizing, using a less efficient engine in more efficient regions (well, the details may vary, but given the same state of development, ...). Something like the 250-range would be interesting, comparing the highest and lowest power an engine can produce at 250 g/kWh, giving an impression of how well the engine overall works, outside peak efficiency. ... big cylinders have disadvantages, too, regarding knock and the like ... in the end, 500 cm³, mildly-longstroked, work about best in regard to ... everything that counts. Bigger cylinders, IMO, require additional stuff to counter those effects, and then may work even better, but, as everything, this isn't free.

  • AmpPum4

    Downsizing busted !!!

    • Zuurker U
      Zuurker U

      Not really. Its just that efficiency is higher if you dont "over use" your engine. By over use i mean that you have to drive like a hyper miler xD

  • Mihails Akulenkovs
    Mihails Akulenkovs

    I've been re-watching your videos about torque and horsepower and thought about EVs. We know now that power is a deciding factor for acceleration. Given that EV motor produces max torque at lower RPM where, due to low RPM, power is the least, and power curve gets to it's wide flat plato of max power at around half the RPM, wouldn't gearbox and a clutch or CVT be a viable solution if EV acceleration was our only concern? Of course, clutch and gearbox are not needed in EV, but IF we were to prioritize constant power delivery, in theory, CVT in EV would allow for faster acceleration from standing start, until wheel RPM matches the motor RPM, at which direct power delivery can be engaged and CVT disengaged, wouldn't it?

  • C P
    C P

    BSFC works when the fuel calorific value is constant, but this isn't always the case. Specific energy consumption, or in this case it would be BSEC, can be a better way of comparing different engines using different fuels. Take an engine running on methanol vs petrol for example, the former has an energy content of 19.7 MJ/kg, whereas petrol is around 46 MJ/kg, yet a methanol fuelled engine, due to it's much higher octane and exhaust water content (therefore a higher exhaust enthalpy content; more available energy to do work), tends to produce more power than the same engine using petrol. Comparing the two is unfair using BSFC unless you account for the difference in energy densities and exhaust product properties by using BSEC instead.

  • Steve

    "Bigger engines are more efficient" alright I'm getting a Viper as my next daily.

  • Duvee Hie
    Duvee Hie

    So you could say the most fuel efficient moment when I'm driving is when I nearly flatten the accelerator pedal at low RPM?

  • Peter Matteson
    Peter Matteson

    In aerospace our equivalent metric is Thrust Specific Fuel Consumption or TSFC.

    • C P
      C P

      Or PSFC (power specific fuel consumption) for turboshafts! :)

  • Erik T.
    Erik T.

    Would be interesting to see the BSFC "islands" compared on a conventional engine, like a plain old DOHC 2.0 L whatever from the '90s, vs the weird semi-diesel stratified combustion and supremely high compression ratio in Mazda's Skyactiv-X.

  • Julio Rodriguez
    Julio Rodriguez

    I remember a few years ago when I used to feel smart because I understand what he was explaining.

  • caboose22320

    i can only imagine someone so fed up with using a quarter tank of gas to get their v8 suburban to work that he and his 44 friends disliked the video

  • Jacob Falk
    Jacob Falk

    12K redline on the Crosstrek, Dam!

  • Niklas Koskinen
    Niklas Koskinen

    Interesting thing I would have liked to see: in the BSFC map, what is the ideal RPM for any power requirement from the engine? As an example, what RPM should a CVT target for any specific throttle input, assuming that we are mapping throttle directly to power.

  • Kyle Eichmann
    Kyle Eichmann

    I always knew it was bad to lug up a hill. It's less efficient than just giving it a little throttle and shifting down to increase your engine load

  • نجارة عصرية وتقلدية
    نجارة عصرية وتقلدية



    Anyone else waiting for the next T50s video?

  • Aaron S
    Aaron S

    I think it would be interesting to compare a 4.0L V8 to a 4.0L I4. Also, why don't economy cars have even fewer, larger cylinders? Wouldn't a giant 1 cylinder like a lawn mower be good?

  • Jeff Burton
    Jeff Burton

    MPG is efficiancy for the entire car as a whole?

  • anthony sorice
    anthony sorice

    hi there i happen to like ur videos can you help me out ,how do i cool my transmission oil i drive on the beach and im at 230 f,how can i lower the temp i cant install a trans cooler i have a 2014 grand jeep,can you help me this thank you i always watch ur videos,

  • Lütfullah Karahanlı
    Lütfullah Karahanlı

    Hey man, can you explain which of these two, SOHC and DOHC, in a perfect world and tune (lets just say perfect engineered, with right springs and size/weight shafts etc) could rev higher? Dual shafts mean more weight and single shaft in theory would rev higher easier; but in a perfect world which one would turn faster thus giving higher engine rpm? I know mechanically the springs are the limiting factor; but if we took that out; wouldnt less mass mean higher rpm? Pneumatic “springs” for example... I dont know man please help; you are the only one i trust 😆

    • C P
      C P

      It's a good question, and although you probably don't trust me (ha!), I can give you my hypothesis (bored aerospace engineer here)... In terms of which would rev higher, this could be interpreted as two questions, which one is quicker to max revs, i.e. idle to redline time, and which one revs higher (higher rpm at the max limit). The first one is less to do with the camshaft arrangement, and more to do with the overall mechanical inertia of all of the moving parts combined vs the stroke length and power per cylinder generated. The lighter the sum of the moving parts, so pistons, crankshaft, camshafts (they do matter some!), flywheel, etc, and the shorter the stroke length (assuming a fixed overall compression ratio, which in reality is more complex), the quicker an engine will be to max revs from idle. The second is linked to the camshaft arrangement, but isn't the main determining factor in absolute max rev limit. SOHC arrangements may be more limited in max rev limit than DOHC due to the need for a rocker system and the reciprocating (back and forth) nature of the rockers. Each time a rocker is forced up or down and then back again, it takes energy (from the springs) to do so, which is effectively an inefficiency. Spring stored energy isn't instantaneous, it has a slight delay, though it's very fast. But as you run to higher and higher revs, that delay and spring energy required to return the rockers becomes increasingly more significant, and the energy inefficiency in the system becomes more apparent. But this is really only noticeable at extremely high rpms, and probably wouldn't make much difference in the vast majority of car engines. DOHC engines are therefore more likely to be capable of higher rpm if all else is equal, due to the absence of the rocker inefficiency. For motorsports engines such as F1 where engines run to extremely high rpm's, they do away with the camshaft entirely and actuate the valves pneumatically, giving greater control and ability to fine tune the timing, rather than be limited by the timing chain.

  • adam fischer
    adam fischer

    Hey EE! What is your thoughts on the Ai designed and mostly 3d printed Czinger 21C. Do you think this would be a safe and effektive way to build cars in the future?

  • Incognito Human
    Incognito Human

    'If you go really lean, you're not going to burn all the fuel going into the cylinder' But going leans means more air, means complete combustion. Why doesn't it burn all the fuel?

  • Chuba

    you look like my thumb, but just hairy

  • PenkillerDIY

    Good video, I'll send it to all of my friends just to remind them why it's never a good idea to tune an engine. BTW, Ford Ecoboost 3.0 at certain speeds almost doesn't discriminate between 5th and 6th gear with marginal MPG difference at 40-50 mph even 4-5-6 gears are marginally different.


    My 2018 Ford focus st gets 5.0 mpg at full throttle and at top speed. Its wild.

  • Carl Sagan
    Carl Sagan

    I feel like this video was done before.

  • John Garrison
    John Garrison

    Motorcycles of any given size seem to get really good mileage compared to cars…..but with a rider aboard they have the aerodynamics of a barn door….so they aren’t doing as well as they might…..

  • leftcoaster67

    So 12 litre 4 cylinder engine is better?

  • Davide Sandona'
    Davide Sandona'

    Hey Jason, wonderful video as always! I don't know if you have already covered the following subject. A couple of days ago I was looking at the launch of the new Nissan Qashqai here in Europe: they are producing two different engines, one of which is a combustion engine that only charges a small battery which is going to drive the electric motors. What I don't understand is the pros of such configuration: there is still an engine running (hence noise/vibrations), there are losses in the conversion from mechanical to electrical energy, ... Did you already cover such configurations in past videos?

  • Joseph Tutor
    Joseph Tutor

    You see, in a crankshaft engine HCCI is impossible because detonation is more than likely to occur too early and it impossible to occur past TDC. Directly at TDC none of it’s sudden and overly violent combustion can be turned into torque because it would be pushing straight down on the crankshaft journal that at this point is parallel to the travel of the piston. So, cam timing and spark events and radiators become obsolete. No valve trains, drive trains or any of the complicated component "trains" contemporarily employed worldwide are necessary or applicable. Direct torque and direct everything is the "only" way to feasibly arrange a design. I also believe that you would be impressed by the suspension concepts in my car design. When "minimal" body roll occurs in my design during extreme cornering the rear tires that are unusually wide don’t buckle along the leading edge and cause the driver to loose traction when you need it most. The front to rear weight distribution of my car is design is base on the golden ratio. I digress or I will go into convulsions from ranting. RSVP.

  • Joseph Tutor
    Joseph Tutor

    I thought I should mention here that the engine I designed fires 24 times per revolution rather than only 4 times per revolution like in a V-8. The single stroke pistons and halo shaped cylinders rotate with all of their mass before engagement to the wheels through an I.V.T. that truly double the torque via flywheel effect. The transmission can also mimic multiple speed transmissions. Supreme, I promise. RSVP.

  • Joseph Tutor
    Joseph Tutor

    I always think you that you’re going to start foaming at the mouth like Hitler. Love the passion bra’

  • Fred Zlotnick
    Fred Zlotnick

    Jason, I saw someone else saying that a particular car had 225 wide tires, and he attributed poorer fuel economy to this compared to 255. I remember you saying one of the factors is the profile the tire presents to the air, so wider would be worse. It seems to me that it is not clear whether a wider or narrower tire would offer more resistance, if you could somehow compensate for other factors.

  • Mikey C Hartman
    Mikey C Hartman

    My hot rods give me SPG...Smiles per gallon.

  • David Lee
    David Lee

    In the BSFC map graph, why is the Y axis set to torque? For a specific given RPM value R, won't the most torque be produced at the point of most BSFC? If not, how will the point with most torque for R be less efficient?

  • Luke Dornon
    Luke Dornon

    MPG is a terrible way to compare the efficiency of engines. It is a great way to compare the efficiency of vehicles, however.

  • Craig H
    Craig H

    Bore of rotary it's huge

  • Luko

    Have you considered an analysis of the cross plane 4 cylinder engine? It’s currently used in the Yamaha R1 motorcycle. It has a fantastic sound akin to the V8 sound most of your viewers would be familiar with. This would be a great engine configuration to introduce to cars. If you can get that great sound in a smaller engine, more people are likely to buy it.

  • Relax Show
    Relax Show


  • Kenneth Scott
    Kenneth Scott

    I would like to see a video on rolling resistance and why vehicles set a standard psi setting while tires can be pressurized higher

  • DaxHamel

    Thanks. Send more please!

  • anydaynow

    Thanks for using metric instead of freedumb units in this video! North American here by the way.

  • David Jimenez
    David Jimenez

    I always had a problem with the term "fuel efficiency" as an absolute measure of efficiency in modern media. Good thing I wasn't the only one.

    • Jay Dunbar
      Jay Dunbar

      Fuel efficiency is simple, it's only an issue when people try to use it to compare vehicles of different categories. For the average consumer its all they need as going further in depth will not make any changes of significance for them. Now if your moving freight, all the rest of it comes into play and can make or break a business.

  • Chris Wilson
    Chris Wilson

    At 9:45 - This is why my larger-displacement Honda Accord got considerably better mileage than the Kia Rio rental I had.

  • David Smith
    David Smith

    I looked into the 10th generation Honda Civic and its BSFC for its 1.5 L turbocharged engine and found it to be at

  • FiveFiveSix (Delta)
    FiveFiveSix (Delta)

    Speaking of semi truck fuel efficiency think of this: • the semi truck weighs 80,000 lbs (total combined when loaded to max legal weight) • it is moving 45,000 lbs of material or items • it does so for thousands of miles across every terrain in the Nations geography • often these trucks get at least 5.5 MPG under these conditions • the useful work being done under this weight for this amount of fuel would be known as extremely efficient if it were a pickup truck however due to personal bias people consider this to be inefficient and bad for the environment • all publicly used vehicles, particularly pickup trucks, have a very low amount of useful work being done with said vehicles and there are a lot more of them consuming "good" numbers of MPG like 30mpg while doing relatively little to no useful work. My conclusion: semi trucks are the most efficient and useful vehicles with the least amount of pollution per unit of useful work and per gallon compared to private vehicle usage in everyday driving. The argument for increased regulations of semi truck emissions is thus moot and highly dangerous to the economy of the United States.


    This is good information. I was unaware of some of these factors. New knowledge, new understandings. You have made some big impacts on my idea for a negative carbon engine system!

  • Chad Jones
    Chad Jones

    Is there something similar for electric cars? Does flooring a Tesla waste energy?

  • Jacob Ingram
    Jacob Ingram

    One of the major reasons most automobiles don't have the highest possible gas BSFC is due to variable RPM and torque. If you get rid of the need for variable engine speeds IE one speed only no need for a transmission you can get pretty decent BSFC. Side note 1: No one runs stoichiometry combustion Side note 2: They are called contor lines or contor graphs Side note 3: Compression exponentially increases complexity. What people do not understand (even most engineers) you can easily go down efficiency rabbit holes. While you might be able to gain a few percentage here and there it comes at extreme costs in R&R, production, manufacturing, and maintenance. Many times it's cheaper (even for the end user) to have a less efficient but cheaper to buy/maintain product. Take Telsa for example from the onset it looks like they are making "cheap" electrical cars when in reality their entire business model is based around subsidies. They made twice as much money last year off of grants from states than they did actually producing cars. This is ignoring grants all around the electric auto industry. This was just from states requiring cars manufactures to make x number of electric cars. It was DOUBLE Telsa's net revenue...... Tesla's likely cost 2-4 times their current market price on the backend without all the subsidies. And somehow their stock is worth more than all auto manufacturers combined? When they hold less than 10% of the market share.

  • Godfrey Poon
    Godfrey Poon

    Broken, Specifically the Fuel Control

  • rtswift

    So it will be more efficient to have 1 giant cylinder than a v8?

  • Daniel Torres
    Daniel Torres

    Way too many adds 1 every 2 minutes is terrible

  • Mark Young - Outside The Box
    Mark Young - Outside The Box

    I want a 4 cylinder motor with the displacement of a V8!

    • Jay Dunbar
      Jay Dunbar

      There's plenty of them, not all v8s are big blocks and not all 4 cylinders are small.

  • Brian Spiller
    Brian Spiller

    The other take away I get is a reinforcement that RPM and peak torque matter even more. However, the use of forced induction is still not ideal. Top gear cruising speed may need only 3k rpm, but doesn't need all the boost. Where is the engine technology that controls boost pressure for efficiency? Also, this discussion shows another fallacy of shopping peak/rpm (that probably is never utilized) where the day to day efficiency matters to more most as people brag about their MPGs. The 0-30 times (the squirt) are more useful than the 0-60 times (the 'drag').

  • Brian Spiller
    Brian Spiller

    I don't understand why Jason went from explaining the the efficiency increase as bore increases and then make a comparison of a 2L-4 cylinder to a 4L-8cylinder. I would have continued the point with two engines with same displacement and same Bore:Stroke ratio and shown the reduced friction area/heat loss area. The 4 would be the more BSFC efficient engine. Additionally it would gain efficiency in operation as peak RPM would be forced down and idle rpm would be down from the 8c. While many people will say the 4c is not as exciting, the discussion is on engine efficiency. Train driving isn't very exciting, but its generally the most efficient Hybrid system in use for the longest time. And the Marine engines... as big as your house, that's efficiency on the BSFC.

  • Ray Bod
    Ray Bod

    So we should all drive one cylinder engines, got it.

  • Titus Mkandawire
    Titus Mkandawire

    What is the best place to start learning all the Tutorial content that you have on your website and youtube channel? I'm studying automotive engineering as a self taught. Any help will be appreciated. Thanks!

  • james caley
    james caley

    So how do modern small turbo engines compare against older, larger displacement engines for BSFC and efficiency? Is all this science and maths a waste of time because the biggest factor for economy is the Sasquatch at the wheel?

    • Jay Dunbar
      Jay Dunbar

      All the science and math still determines the range of efficiency possible with a engine, and how easy or difficult it is for that sasquatch to drastically effect the fuel consumption. A good example is my old 1999 Freightliner with a 3406e cat, if I drive it right I can get 7+mpg at 80,000 pounds gross, if I run it hard I can get 4mpg. A new truck the range is in the 6-8mpg range depending on the driver.

  • Eric Perkins
    Eric Perkins

    ICE engines are dead, so is content that explains it. This content is going to go the way of the horse and buggy.