The Best Way To Compare Engine Efficiency - BSFC

Brake Specific Fuel Consumption - How Massive Engines Can Be Efficient
Comparing Engine Performance: BMEP - • The Best Way To Compar...
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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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[@EngineeringExplained]

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: kzbin.info/www/bejne/mHbCYn2Pp9GMj7c

[@rlpatton1970]

Isn’t the Mercedes F1 engine the worlds most efficient?50% ?

[@MBuilt]

:cries in rotary efficiency:

[@user-yz6kc4xn4r]

it's worth also to note that big marine 2-stroke diesel engines are among the most fuel efficient engines, for the same reason that they have less friction losses for a single cycle, compared to 4-stroke

[@sbelllido]

You are absolutely right. The main purpose of an ICE is to convert the fuel chemical potential energy in mechanical work at the main shaft. How good this process inside the cylinder enclosure has been done is measure by ISFC, and how good this energy is transported through the mechanism is measure by BSFC. Excellent explanation if the topic!!

[@Platypus_Warrior]

Why is there a naked man drawn upside down on the upper left quarter of that white board?

[@starvalkyrie]

*Jason produces a thermodynamics textbook* Oh... it's about to get real.

[@mod.ts76]

it's just a massive textbook with photos of whiteboards as its diagrams

[@labourlawact7826]

Leave him. He's cool.

[@YounesLayachi]

Jason flexing the 1 take 1 breath video xD

[@blzt3206]

My favourite profs in university taught the same way you do: Original notes written on the board. My least favourite profs made slideshows and talked briefly about each slide - leaving us to our own devices to really learn the material. Thank you for being such a great teacher.

[@YounesLayachi]

Keep in mind Jason may be a good prof but he has prep time to fill the whiteboard, a prof typically does it on the fly. It is very rare to find a prof that can do purely notes without errors and unreadable crap Ideally a prof should do a mixture of both (slides and notes where appropriate)

[@blzt3206]

@@YounesLayachi it's not rare at all. Profs have TAs they can get to write notes as well. You're just making excuses for laziness. The profs I liked the most happened to be the busiest but they were the smartest and most capable at their jobs. The ones who read off slides just suck.

[@YounesLayachi]

@@blzt3206 you're angry and it's okay. I too hate the slide readers with passion. But the reality is, extremism is always detrimental. There should be nuances, slides and whiteboards each have pros and cons. So they should be used in conjunction

[@Shenron557]

I don't know which is the most optimal approach. Writing on the board during class takes time (time which can otherwise be spent on covering the syllabus). Moreover, students tend to get distracted and start talking when a professor turns his back to write on the board. On the other hand, pre-prepared slides gives more time to teach and minimizes or avoids the issue of students getting distracted. However, I also feel that writing on the board makes the class more engaging and stimulating for students who really want to listen and learn. So probably a mixture of both might be good.

[@nateverge1167]

I had a prof who would have my entire class of MSE students (~150) walk half way across campus from the department's building to the architecture building because it had a projector the biggest whiteboard.

[@Ckcfuxucu]

I started watching your videos 4 years ago. Now I’m taking an internal combustion class in college where we are calculating this and a lot of the other things you’ve talked about. Thank you for continuing to make these videos. I give you credit for convincing me to go to college by showing just how interesting this stuff is.

[@tanuki6666]

*Jason Summons Thermodynamics book* **The screech of thousands of students suddenly heard in the distance**

[@scottymonochrome3795]

Have you considered spending some time teaching at an Institution of some kind? Your ability to articulate these complex ideas in a robust & simple way is immeasurably valuable. We need enthusiasts such as yourself, bringing forth excitement into otherwise boring fields. Thank you, as an academic, for your contributions. I am much more knowledgeable because of my Subscription to Engineering Explained

[@EngineeringExplained]

Thank you for the very kind words! For now, KZbin is my institution haha.

[@mrburgermaster]

I'm not sure how much money he can really make as an instructor with a Bachelor's (unless this is different to what I heard years ago). Academia can be this steep hill climb of pursuing a terminal degree, spending countless hours assisting in research, and even then, having to consistently publish just to make a name for yourself, get tenure, better benefits, etc. I wouldn't be surprised if he did it in the distant future despite this, assuming finances are great.

[@TheSteinbitt]

He’s doing more good here tbh, we all get to learn!

[@onetrickhorse]

@@mrburgermaster That is an incredibly accurate summary description of academia. To even get in the door, a masters (by research) is the absolute minimum prerequisite, with a PhD being essential if you want any respect at all in academia. And having said that, even then you're at the bottom rung of the ladder, and will be saddled with the least interesting roles until you can produce something worthy of note in the research world, or better yet, attract sufficient funding from industry or institutions, that gets you noticed. The bit I hated about academia (whilst doing my PhD) was exactly as you mentioned, publishing papers like you're shooting buckshot at a barn door. The difference between industry and academia when it comes to research I find is the difference between quality and quantity. When I completed my PhD, I entered industry, and now I get academics constantly pitching research to me, and I get to choose who I do and don't fund/collaborate with, and I have nothing but sympathy for them, because they're often incredibly clever individuals reduced to this kind of professional 'pole dance' routine they have to perform towards industry just to make a living that is constantly under threat. Academia is a world I'd only ever consider going back to when I retire, part time, as a consultant, otherwise I'll stick with industry as long as I'm relevant!

[@Ryan.......]

I would be absolutely amazed if he doesn't make orders of magnitude more money per "lesson" here in addition to reaching far more people than he would directly teaching. My comment is from the perspective of a high school physics teacher, so my work flow is different than a lecturer at a university. One thing to consider when it comes to standard teaching is volume of teaching output. On KZbin, Jason can take several days to plan and deliver a single, polished 10-20 minute video. When teaching, you are doing several of those every day (in my case it is ~20 per day) in real-time. One other thing to consider is that here, he has an intrinsically motivated audience who knows they don't have to demonstrate that they actually understand what he teaches, don't have to attend every lesson, and he doesn't have to go into nearly as much technical detail (though I do appreciate that he often goes into a fair amount of technical detail). I use a lot of videos from sources like Engineering Explained in my instruction along with elaboration and discussion. In addition to the standard KZbin viewership, I think this is, by far, the better model for Jason to have the greatest educational impact while also probably making much more money.

[@RaphYkun]

Would having a CVT tuned at BSFC as the shift point be the most efficient way to drive on an ICE car?

[@ethanhenry5873]

Yes, but it also is related to road traction, internal vehicle weight and road grade as well. This is similar to what the larger car companies are programming into their ECMs and TCMs now, but it's unfortunately not an exact science as I understand it.

[@abhishekreddy2425]

Even I want to know.

[@devinwalton408]

Too many variables, but in an ideal scenario, yes. The way you use the throttle has a huge effect on efficiency. The coeff. Of drag and speed you are travelling has a huge effect on fuel economy.

[@ASJC27]

Yes, using a CVT to keep the engine at it's BSFC/efficiency peak will give the best economy at any given speed.

[@lucasvanhamburg4937]

as far as I know cvt's use belts, which are not efficient. gears in a mt have less losses.

[@tangydiesel1886]

It is pretty amazing how efficient over the road trucks and trains are in how much weight they can move per unit of fuel.

[@ninemilliondollars]

Trains have a very low rolling coefficient of friction between the wheels and the rails which gives them that efficiency.

[@borysnijinski331]

@@ninemilliondollars also do not go up steep hills.

[@ninemilliondollars]

@@borysnijinski331 Trains have sand tubes that deposit it on the rails just in front of the wheels to help with traction going up hills.

[@nothingsurprisesmeanymore]

True, the trucks I drive will do 8.3 mpg (US gal) but weigh 44 tones or 97,000 lbs

[@jaydunbar7538]

@@ninemilliondollars trains don't have steep climbes anymore, 4% max if i recall correctly. The long term fuel savings greatly outweighs the up front cost of reshaping the grades. Out in the western mountains there is old tracks abandoned all over with tree's growing through from when the new low gradient tracks went into service.

[@wibuwe]

You know what they say: "there's no BSFClacement for displacement"

[@spicemasterii6775]

I'm so glad to have found this channel. Things I learn here are amazing! Thanks for the education!

[@maxreemtsma4955]

I'm always impressed with how much I learn from your videos. Keep being smart.

[@peanut71968]

Thanks, Jason. Explained and illustrated so very well! Cheers!

[@callumross406]

hey man, just letting you know i enjoy your videos and theyre really informing and helpful

[@SkywalkerTibor]

Fantastic explanation. Thank You!

[@atefelabed8365]

As always thanks for these informative videos. I suggested a few times a video explaining the reason for the different placements of brake calipers between different cars but also between front and back brakes of a same car. Plus the difference between standard calipers and the new 10 piston calipers seen on recent Porsches and whether it really makes a difference. It would be nice if you could explain this. Many thanks

[@Math-zl8kq]

Finally a video I’ve been waiting for years. Do you have any link in order to find any specific car engine BSFC? They rarely disclose that information.

[@rrr32__4]

Good timing, we were introduced to BSFC in uni yesterday, great video.

[@orppranator5230]

What was the class called?

[@sail4horizon]

This reminds me of some old software I used to play with as a kid called Engine Analyzer back in the early 90s. It was great fun to play with all the combinations of port sizes, cams, etc. to come up with the best combinations. That's where I first learned of BSFC. Wish I still had it (it was on floppy disks)

[@dhruvgupta1377]

Man sometimes i feel like youtube does not do justice for your talent, the way of your explanation and your knowledge is epic love your videos thanks for making these videos so that people like me gain ton of knowledge 😁

[@MrHarr0073]

I agree. 29,030 views at this moment. not likely a teacher in a university setting would reach this many people in a classroom type setting

[@dhruvgupta1377]

@@MrHarr0073 i don't mean that in any way all I was saying is that the amount of hardwork he gives i feel youtube can't to a justice will countering it with the revenue element.

[@TestingPyros]

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!

[@CullenCraft]

This is great! I always struggle to explain why my boat's two 454 engines aren't as inefficient as they seem at first. More POWAH!

[@dougrobinson8602]

Yes, and you have propellers that have a lot of pitch in them to prevent over-revving those engines. That loads your engines greatly, which helps BSFC.

[@simonthebroken9691]

Thanks. You explain this stuff so well. I understand the premise, but I have trouble explaining things to people. The phrase, "use your words" comes to mind.

[@teaganroehl]

Literally my favorite channel

[@AustinPerdue]

About time this video came out. Thank you!

[@AustinPerdue]

My 2000 Insight engine is ~200g/kwh, and thus is around 40% thermally efficient. I can see over 100mpg cruising on the highway in good conditions. I'm surprised that modern engines really haven't come very far from this figure.

[@dt3268]

Excellent explainer. Concise. Good examples. You must be an excellent engineer! :)

[@richardjones7386]

Correct me if I’m wrong but my takeaway from that is that for daily driving it makes sense to use the engines efficiency to accelerate, say 70% throttle, to a given speed and then maintain that speed. Not to accelerate gently to that speed as its inefficient use of the engine. Driving teachers in the UK tell us that gentle acceleration is best / more fuel efficient. This disproves that logic. Excellent.

[@EngineeringExplained]

They're actually correct, but it's a complicated story. Generally speaking, it's better to accelerate more slowly, because this results in a lower average speed, and a lower average speed will have less losses, and thus use less energy. But it's a balancing act. An engine operating at a more efficient spot doesn't necessarily mean you're getting better MPG. Example: driving at 90 mph, your engine might be in an efficient spot, but your aero losses are massive, so you have to make a lot of power, which means bad fuel economy.

[@thegr8stm8]

Fascinating, Jason.

[@judo-rob5197]

Another great video. Thanks.

[@danellerbe1521]

Awesome explanation!

[@InnovationDiscoveries]

Interesting topic and Fantastic explanation.

[@willb3018]

Excellent as usual.

[@trevorbarkiewicz5035]

That Thermo book looked familiar, so I go mine out and turned to page 79 to read the heat value definition as well.

[@tkrey23]

great video. I've wondered about fuel efficiency at high load/low RPM vs high RPM/low load forever. Thanks!

[@hadimezher1336]

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

[@EngineeringExplained]

Happy to hear it, thanks for watching!

[@kartdude2006]

Great video, next one should be on BMEP 👍👍

[@lonnymo]

Interesting topic. You did a good job explaining a subject that is actually very difficult to understand. How about comparing electric power? Interesting, Thanks!

[@RahulPatel-fp3ju]

This is super interesting. I think you should do a video on the Liquid Piston rotary engine. Super simple, high power density and efficiency.

[@lonnymo]

Sound interesting!

[@RahulPatel-fp3ju]

@Donovan Piko True, but there is some decent info out there.

[@kevink2315]

At 9:34, Jason gets into the ratio of surface-area to volume of a a cube and a cylinder, and the lower the ratio is, the higher the efficiency (and the lower the BSFC) I had done a similar calculation for a rotary engine and compared it to a Porsche 944. As I recall, the rotary had a much higher area-to-volume ratio vs the 944, suggesting a higher BSFC.

[@RahulPatel-fp3ju]

@@kevink2315 yeah the rotary engine does have a pretty large surface area relative to its volume. But the Liquid piston engine supposedly gets close to 70% thermal efficiency. I guess another way would be to use a low thermal resistance coating to reduce heat loss to the cylinder walls

[@kevink2315]

@@RahulPatel-fp3ju I have seen 75% thermal efficiency in one article. Swain has been coating pistons and other engine parts for a decade(s), and would help here. The LiquidPiston engine is enough like the Wankel to be close to the same area/volume ratio,

[@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.

[@bravechicken6251]

Great work.

[@DaxHamel]

Thanks. Send more please!

[@thomaspatrickwilson]

I have been watching your videos for YEARS. As always, another well-done video. Have you ever considered teaching automotive, motorsports, or mechanical engineering at college level or higher?

[@marcokrueger3399]

Really good video, thank you Jason! btw, that's a really cool speedometer with a maximum at 60mph, but engine rpm up to 12000. Neat! :D

[@mikechiodetti4482]

One thing you touched on was the efficiency gauge that gives you immediate MPG numbers. Mine is between the tach and the speedo. 40 is at the top, what you aim for, and even on a freeway at 70 MPH, using that gauge as a guide to where the throttle (or cruise control) application keeps the vehicle at a steady speed and yes do climb as I've seen them go over 40 MPG. Doing that really helps the "average" number for MPG at the gas pump. Course it's a (light vehicle) 2020 RAV4, on a fairly flat road, with the wind at your back. Driving back with the wind in front of you, MPG does drop some. It only takes one variable to change that.

[@porterdallenbach1639]

Cool video! We use BSFC for our SAE Clean Snowmobile Challenge my university competes in! Video idea: Fact-check and discuss possibility of a hovering Tesla Roadster using high velocity air from a bottle.

[@aerok89]

You are right, larger does not mean is better. But I want to point at my personal experience using a 5.0L 2018 Mustang, and I am impressed with the fuel efficiency, it has a 11:1 compression ratio (I think), and it averages 11 km/L [26 mpg]. In my mind one of the best engines I have tried. Without entering that it revs 7500 like crazy for a V8. It's like a 90's Honda hahahaha. Great content!

[@sylak2112]

Nice! More math! This video comes timely. I had a discussion last week about engine efficiency. I remember you mentioning, in a previous video, how ICE are more efficient in higher load/lower RPM scenario, so I use that knwoledge and I was talking about that, when Someone told me " it is inaccurate, gasoline are better at higher RPm diesel at lower" . The people in the conversation were confusing Fuel consumption and torque production as efficiency with thermal efficiency. But, I'm just a IT tech, I can't explain those thing well enough, So I wa not able to do it at that time. But now, we have Jason coming to the rescue with more MATH!! ( I love math). na na na na MATHMAN!

[@labourlawact7826]

Hello Jason! 👋👋 Hope you're well my friend☺😊☺😊👍👍

[@RidoAdimas1]

Finally, I can share this video to my family who still believe 1 liter engine is more fuel efficient running at 4000 rpm at 100 kph than 2.5 liter engine running at 1600 rpm at the same speed. Thank you, Sir!

[@yusufkuntoro3141]

Smaller engine isn't mean more efficient, so many car manufacturers only focus on weight reduction.

[@nikolamadjarov2226]

Wow!!! That is academic excellence!

[@matthewdufty606]

Excellent

[@vinnytube1001]

Do you do requests? It would be fascinating for a series on the efficiency impacts of hybridization. I know it's a combination of braking regen, electric assist, capture of excess power/electricity, but (and here's the tie-in to this video) I think there's a component of keeping the engine at its most efficient zone during electric assist (if not shutting it off), or in the case of Honda, keeping it in the most efficient zone for use in a serial hybrid configuration. I'm curious about how each one of these aspects of hybridization effects the overall fuel consumption, i.e. which is the largest contributor? And since BEV also use braking regen, how much of a player is that in BEV range? (I think you may have already covered that last one...) Keep up the great work.

[@theesperanzacompromisebyja9044]

Informative.

[@the_Scarlet_one]

Did you just use 3D text for 20 MPG and 30 MPG? Isn’t that what the whiteboard is for? They were so fancy! Keep it up. Always enjoy these videos.

[@waduhek2568]

Sad that this isnt getting more views...

[@Knackebrot]

My driving school course book (Austria) even tells you to accelerate like this. Not very indepth but it says you should give it about 3/4 throttle at medium rpm. Then be in the tallest gear possible, except if on an incline.

[@ikt32]

So the lesson I got out of it: Get a massive four-banger!

[@Shapparaal]

Hence the 2.7L turbo 4 in the Silverado.

[@marcokrueger3399]

Or get a Lanz Bulldog or something of that kind. 6.2l 1 cylinder Diesel engine. Can't get more efficient than that!

[@abccanada6248]

@@Shapparaal EE did a video on why that engine is ineficent asf and a fuel hog

[@TimpBizkit]

​ @Marco Krueger I'm driving at peak BSFC but my Speedometer is going 100, 110, 120, 130, 140, 150. How do I get BSFC at a reasonable speed? That's when you go back to smaller engines. That is unless you just tie 10 cars to each other, turn 9 of them off and have one pull the group. Then swap the lead car so everyone uses fuel equally.

[@social3ngin33rin]

that's super awesome :) and interesting

[@Davide_sd]

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?

[@batista9419]

I have a question: how can you have any question when this video has such a simple explanation that is easy to understand?

[@LazerLord10]

This is all really neat stuff about engine dynamics! However, MPG is still the most useful way to look at the efficiency of a car. After all, it's MPG to move stuff, which could change between vehicles using the same engine (see Honda accord vs Element). This message brought to you by the small-car gang.

[@CertifiedSlamboy]

You're right. This is more about efficiency of the 'engine' though, not the efficiency of the 'vehicle'.

[@johnwaterhouse4909]

As a truck driver, I say mpg or l/100km but divide that by the total mass. I'm averaging 36.3l/100km but that's moving 80,000 lbs. I think I'm doing pretty good

[@thorin1045]

@@johnwaterhouse4909 yep, both system compare the engine, but the real question is the useful part, don't really care about the 1 ton of the cars own weight, if it only moves a single person, it will be much worse than the bus with a more fuel using engine and 10 ton or more own weight, but moving 80 person.

[@Chuckiele]

@@johnwaterhouse4909 Id rather compare it to the weight requirement of the task, not the weight of the vehicle itself. If you used your unloaded truck to drive your kid to school, thats not very efficient.

[@nothingsurprisesmeanymore]

I drive a 15 year old Renault Grand Scenic it's a 7 seater with a 1.9 litre diesel engine with a 6 speed manual. This is not an exciting car but I will get 58mpg (US gal) on a run this is with 5 people on board and a full boot (trunk) weighing about 2 ton. So why are Americans happy with cars that return 40mpg or even less?

[@borysnijinski331]

Now I understand Volvo Penta’s design philosophy behind their marine diesel engines. I thought 3.7litre diesel was big for 4 cylinders (D4-270), but it now makes sense.

[@hueywallop2461]

Future video topic suggestion: Building on your explanation of BSFC, describe the effects of fuel composition (Octane rating, oxygenates, etc.) on BSFC for a fixed engine type(s). Thanks.

[@simonecominato5561]

Crystal clear! :)

[@MetroidChild]

Another plus for large volumes and relative stroke lengths is lower friction relative to power, due to the same principle as the volume to surface area ratio (squared instead of cubed though).

[@franciscosaavedra6105]

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

[@battlepug3122]

I know you're not getting the Toyota GR Yaris in North America but it'd be awesome if you could do an analysis of the G16E-GTS Edit:- I think you're getting a GR Corolla with the G16E-GTS in North America

[@yungboicontigo9278]

I hope so, with AWD like the Yaris. If it’s FWD I will be so disappointed 🤦‍♂️

[@johnlincicum6390]

I want that GR Yaris 6 speed so bad!

[@ghoulbuster1]

He already did a video about the three cylinder yaris engine

[@battlepug3122]

@@ghoulbuster1 I've seen a video on the Koenigsegg 3 cylinder but nothing on the G16E-GTS. Do you have a link?

[@utubejdaniel8888]

Airplane designers are greatly concerned with BSFC. Most air-cooled engines in light airplanes have a BSFC of 0.5 lbs/horsepower hour. This is used to size the fuel capacity for the airplane.

[@chippyjohn1]

That is why air cooled is poor design, they use about 50 percent more fuel than a modern liquid cooled engine.

[@wowgggearing]

yyeessss, nice, efficient driving

[@larssonk22]

Please do a review of the McLaren Artura! With the exception of Carfection everyone just reads off the tech sheet, nobody has tried to explain what all the new tech could potential mean for the driving experience.

[@ivanjovanovic362]

That's right. Don't use MPG, use L/km like normal people

[@lucasvanhamburg4937]

you mean km/L

[@ivanjovanovic362]

@@lucasvanhamburg4937 No, I mean l/100km my bad

[@hojnikb]

according to wiki, my 2.0 bimmer nets 198g/kWh, which seems awsome! And it really shows, under ideal conditions i can crack 60mpg quite easily. And thats a 1.5t boat with rwd and no hybrid nonsense.

[@AustinPerdue]

This a diesel?

[@hojnikb]

@@AustinPerdue Yep, N47 diesel.

[@AustinPerdue]

One thing to keep in mind with diesel is that it has at least 15% more energy per unit volume. A comparably efficient gasoline engine would be around 230g/kWh.

[@gort8203]

Please consider doing a video comparing sleeve valves to poppet valves.

[@apexseal2811]

Thanks to traffic and irregular road slope, I could never manage to measure fuel consumption vs. RPM through a basic OBDII dongle (the car has no OBC). So pretty neat to have the results here -at least I get the idea.

[@RaddestDad]

What a great video. I 100% agree. Pretty sure my 5.4 Ford V8 Expedition has a better BSFC than my Subaru Ascent 2.4 turbo. Both get the same mixed mpg but the V8 is in a 1500 pound heavier vehicle.

[@ExOAte]

That might be true, but if you don't use all that potential energy the smaller Subaru might still be the better car for daily driving. A container ship might be more efficient but doing groceries with it is pointless.

[@EngineeringExplained]

Maybe so! Or if the 2.4L is working at a high load frequently, putting it into boost, with a rich a/f mixture, then real world mpg can be down.

[@anydaynow01]

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

[@oldretireddude]

Thanks for the video. I have an additional MPG topic that I would like to see someone tackle and that is KZbin 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.

[@FuncleChuck]

Absolutely accurate, yet almost entirely useless to a consumer.

[@EngineeringExplained]

Channel motto! 😂

[@RaddestDad]

We need smarter consumers

[@cls63amgwagon34]

@@RaddestDad it’s not about education, this discussion just really isn’t relevant to consumers. They need to know how efficient a CAR overall is vs another CAR as a total. Like he said in the beginning, a Semi can have a hugely efficient engine, but it’s still a Semi getting 20 mpg, when that same person can just drive a moped and get 30... the point of the video is how to measure efficiency of ENGINES for other means, ie research, personal curiosity, etc

[@EssenceofPureFlavor]

I find it pretty useful and I'm a consumer. Nobody's forcing you to watch these videos.

[@FuncleChuck]

@@EssenceofPureFlavor you seem to think I dislike the content, but I’m also an engineer and I love this stuff. However, thermodynamic efficiency doesn’t matter when you’re buying a vehicle for transportation, but MPG does.

[@HasbullahSyarah]

The theoretical limit for thermal efficiency, if you have unlimited amount of money, is about 60%. F1 engine is at 55%. Pretty amazing . Thanks Jason! It's been a while since I see that Cengel and Boles 🔥🔥

[@hojnikb]

combined cycle engines can crack that 60%.

[@chippyjohn1]

Actually it would be higher. F1 restricts the use of ceramics for pistons and bores. CSIRO did efficiency testing back in the 80's with ceramics and achieved efficiencies of around 60%. Think of how much higher it would be now with modern electronics and injection.

[@schwazeneggro4274]

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

[@VARITHMS]

I'm glad you said this. Everyone that drives a f150 wants to compare fuel efficiency (mpg) between the 3.5L twin turbo vs the 5.0L naturally aspirated V8. The 5.0 gets the same fuel mileage as the 3.5L V6 but produces almost 100ft/tq less. If the V8 produced the same power numbers the fuel efficiency would be less than what it is.

[@DavidTeleiosis]

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

[@stevesloan6775]

Definitely struggling to get my head around this measurement. Mainly the capacity thing. Proper squish designed into your combustion chamber the better. Literally take a mould. 😎🤜🏼🤛🏼🍀

[@jeffarcher400]

Kinda blew right through pumping loss. I'm guessing it's the difference between max possible volume per cycle and observed volume due to restrictions in flow. It's great to get to use boring things I learned long ago to understand something really important. Thanks.

[@zoefaith120]

It's all in the Numbers!

[@johnnyx.1186]

I don't understand the " Chinese" on the board lol, but as a consumer i find this much more important than mpg. After all, a 30mpg vehicle doesn't necessarily have a more "efficient" engine than a 20mpg vehicle. Thanks Jason.👊🏾

[@Optimistprime.]

I drive a 2016 Toyota Prius v and with the specs I've found on my engine, with my Atkinson cycle (which is really a Miller cycle) my engine is about 38% thermal efficiency. Yay for me! One thing that is worth mentioning too, is if you have a scan gauge ii or a simular device, you an actually see how RPM can effect your litres per hour. If im driving down the road and getting say 4.5L/100km but my rpms are say 1800, once my CVT changes ratios and drops it to 1200, I may still get 4.5 but im using less fuel to get that number.

[@stevesedio1656]

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.

[@SuperFredAZ]

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.

[@gordonwbell]

Why are you not a teacher or professor?! Lol honestly. I love this content. I can’t get enough. If I had a physics teacher like you, I probably would’ve done better.

[@settjessettje9323]

Low cycle fatigue. Suggest you do video on Chevy V8 engine manifold bolt failures. Should be a nice exercise for you.

[@Colonelloki]

Y’know, I’ve watched your stuff off an on for a few years now, but I just can’t handle you giving all of our engineering secrets away to those not trained in the arts! If I hear you mention exergy every, I think I’ll have to assemble the order of the engineer and deal with you….

[@abelalonsoballonaguirre5191]

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

[@Stallion8888]

I see you as an intelligent person but when you brought out a book, damn you are a scientist!

[@timmallette1888]

The sailboat!!!! I used that book

[@ibrahimqari9189]

Thanks. Heavy stuff

[@stefanjetchick3853]

Very interesting, thanks! (maybe we need another metric: GSYC, Geek Specific KZbin Consumption ;-)

[@IceInMaWeiner]

Awesome video! How would I calculate the most efficient rpm to cruise at in 6th gear? I always burble my Mustang down the highway as low as possible but this video now tells me that that isn't as fuel efficient as it could be!

[@matthewmartel9295]

You should be able to find a BFSC map in the owner's manual.

[@EngineeringExplained]

Generally speaking, lower will be better. The faster you go, the more aerodynamic drag you have, so even if the engine is in a more efficient spot, it has to make more power to overcome drag, and thus worse fuel economy.

[@AustinPerdue]

Reiterating what Jason said, generally speaking, fuel economy falls away as speed drops. I find my fuel economy is highest at the lowest speed I can shift into the highest gear. Most vehicles would benefit from having an extra gear or two on top.

[@jonathanstensberg]

Assuming this is a modern Mustang, Ford will have already done the work for you by selecting a highest gear that maximizes fuel efficiency for the offical highway fuel economy test. The average speed in that test is 48.3 mph (with no stops), so your Mustang will most likely be most efficient driving at 48.3 mph in its highest gear, give or take a few mph.

[@PSWii360onBaSS]

@@AustinPerdue This I wholeheartedly agree with. I have an 06 G35 Sedan with a 6MT, and 6th gear at 70mph gives me +/-3000 rpm. A 7th gear would bring it down to at least 2k.

[@SkunZielonyJakMech]

Lowest BSFC is on the lean side. The reason is, if we put some additional air into the cylinder, we reduce pumping losses (because higher pressure in intake manifold is needed to pass additional air) and heat losses (because of lower peak temperature). Also dissociation of triatomic molecules like H2O, CO2 is less pronounced and dissociation is endothermic process. We're limited in leaning out mixture by emission (three-way catalyst works best in stoichiometric AF ratio) and limit of ignition (the leaner the mixture the harder it is to ignite it), otherwise all cars would run lean for economy.

[@ColeSpolaric]

It would have been interesting to see how a square bore vs over bore vs under bore would also play into this.

[@EngineeringExplained]

I have a video explaining how bore/stroke impact efficiency if you're curious! kzbin.info/www/bejne/i4eWg6p4hdatpLc