Bore vs Stroke - What Makes More Power?


What Makes An Engine Better? Big Bore vs Long Stroke
Bore and stroke cause differences in both power and efficiency.
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All piston-cylinder internal combustion engines have a choice to make with regards to bore and stroke. Should an engine have a large bore (the width of the cylinder)? Or would it be beneficial to instead have a small bore and a long stroke? Or should the bore and stroke dimensions of the engine be identical? We'll discuss how bore & stroke affect engine RPM, engine airflow, heat losses with regards to surface area, and flame duration. What makes the most power may not always be the most efficient.
With regards to bore and stroke, an engine is called "oversquare" if the bore is longer than the stroke, "square" if the bore and stroke are identical, and "undersquare" if the stroke is longer than the bore.
SAE - A Study Isolating the Effect of Bore-to-Stroke Ratio on Gasoline Engine Combustion Chamber Development
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  • Zatiti Cherry
    Zatiti Cherry13 timer siden

    Very close to the K20 and K24 geometries; did you use them as semi starting points when you did this?

  • Miami Aqua Life
    Miami Aqua Life7 dager siden

    My girl left me for a guy with a bigger bore and longer stroke. Thanks for explaining why.

  • Ivan Walker
    Ivan Walker8 dager siden

    Brilliant but, pleeeeeze, take a breath.

  • Last Prophet
    Last Prophet10 dager siden

    girth >length 🙄🙄🙄 that's what she said.

  • 1908Rick
    1908Rick11 dager siden

    Ever been so bored you have a stroke?

  • rick dees
    rick dees13 dager siden

    Women should have an opinion on this.

    DANI BENGKEL17 dager siden

    Masayang-masaya ako na nasa komentong ito.bati ng motor automotive

  • luke pruski
    luke pruski18 dager siden

    Amazing content would not look anywhere else for my car info.

  • Kendrick Green
    Kendrick Green20 dager siden

    Hey great video. Will you do a video on why a NHRA Pro Stock engine makes so much horse power with no forced induction?

  • Dean
    Dean20 dager siden

    Most of this went under my head

  • Michael Walker
    Michael Walker22 dager siden


  • Peter Dalemans
    Peter Dalemans27 dager siden

    I am missing a item; power has two components a static and a dynamic component. It is the dynamic component that creates friction and that means losses. Therefore a low revolution long stroke engine. What is remarkable is that the piston speed of a normal car engine is about the same as a big ship engine with a 2meter stroke

  • Zac Le
    Zac Le29 dager siden

    6:08 His calculations are wrong 117mm bore will have intake valve = 117*30/80 = 43.88mm 86mm bore will have intake valve = 86*30/80 = 32.25mm 63mm bore will have intake valve = 63*30/80 = 23.63mm intake area (bore = 117mm) = 43.88*5*2*3.14159265358979/100 = 13.78cm^2 not 25.2cm^2 intake area (bore = 86mm) = 32.25*5*2*3.14159265358979/100 = 10.13cm^2 not 18.6cm^2 intake area (bore = 63mm) = 23.63*5*2*3.14159265358979/100 = 7.42cm^2 not 13.7cm^2

  • belltocher
    belltocherMåned siden

    One very important resone stroking an engine gives you more power is because of the longer arm off the crankshaft gives a piston more leverage in turning the crank . also the Piston moves the slowest at the very top and very bottom of the stroke , with the crank pin being farther from the Centerline of the crankshaft and therefore turning a bigger Circle the extra dwell time at the top and bottom of the stroke can greatly increase the amount of time that there is for proper cylinder filling and exhausting. Rod ratio is also a consideration in designing a motor that's the ratio between the stroke and the length of the connecting rod. Longer stroke usually means longer Rod which means bigger engine size.

  • Swearingfruits
    SwearingfruitsMåned siden

    Can you still a lot of horsepower with long stroke

  • Leslie Tolman
    Leslie TolmanMåned siden

    Ok kids, what I learned is bigger bore, bigger pistons, shorter rods, bigger vales are what I'm chasing and that I have zero clue what I'm doing from there lmao. Coming soon: Leslie threw a rod or, if I'm lucky, it just won't start. Good hell. P.S. this math is killing my head. I have much to learn!! I'm not rebuilding my engine yet but I don't want to do it again until I've had a good amount of time on the first build lol. Pretty cool stuff but yeah looks like I need to get in some college courses so I can further my abilities. And I thought the timing belt replacement job I did was difficult. Ok. Bring it.

  • Kostyantyn Rybchuk
    Kostyantyn RybchukMåned siden

    Couldn't catch the point: on the begging it was told that shorter stroke rotates faster and to a higher rpm. However at 14:14 longer stroke explained to rotates faster..

  • Tim Harrington
    Tim HarringtonMåned siden

    Careful: 25 centimeters square is not the same as 25 square centimeters. 25 centimeters square is 625 square centimeters. 25 square centimeters is 5 centimeters squared . Two very different things. The order is important and so often overlooked. You have the most informative and interesting videos.

  • Matt Torres
    Matt TorresMåned siden

    On a 2 stroke engine, is the displacement calculated using the stroke the piston travels before the top of the exhaust port, or the total travel? After all, zero power is being developed while the top of the piston is passing the port.

  • Σταμάτης Καλλιόστρας
    Σταμάτης ΚαλλιόστραςMåned siden

    9:30 Pretty sure its mm squared and not cm squared, right?

  • Rich MAC
    Rich MACMåned siden

    In every video you have regarding this engine power you almost completely disregard torque. The longer stroke engine is going to make more torque and be more efficient. The high reving, big bore, short stroke engine is going to make more HP (at high RPM) but it's going to be a complete dog until it's reving at high RPM. Conversely the long stroke, small bore engine is going to have a lot more torque down low but be incapable of turning at high RPM's. This is why most street engines shoot for the square cylinder design (bore diameter = stroke length or close to that).

  • gerald alforte
    gerald alforteMåned siden

    I Armando C. Rabino Automotive Mechanic of, TESDA It's wonderful demo, watch, and Hear me. In this video, additional my personal experience. I like this Demo in English Language. Very clear to my experience. Thank you. Engineering: Bore,vs stroke - what make More Power.

  • Tim Copeland
    Tim CopelandMåned siden

    great explanation .. Thank You for sharing

  • Anthony Cadiou
    Anthony CadiouMåned siden

    Excellance !!!!!!!

  • S B1
    S B1Måned siden

    I would like to see a similar presentation on the optimization of a single cylinder normally aspirated gasoline SI four stroke engine. I am of the opinion that approximately .5L is a good compromise for power and efficiency. I need you to verify or refute my opinion. Thank You

  • Herysul Sulatan
    Herysul SulatanMåned siden

    Thanks for the good info. More power

  • Huy Vũ Văn
    Huy Vũ VănMåned siden


  • Ivan Daniel
    Ivan DanielMåned siden

    so rad! thank you fir putting this together... now take a breath and a sip of water!! 👌🏼

  • Michael Tubov
    Michael TubovMåned siden

    Fantastic theoretically. Thank you very much Dude. Please some day explain boxer engines (undersquare) on LPG fuel. Thank You for Your perfect expert explanation for everything. Thank You Very Much!

  • Dennis Wilder
    Dennis WilderMåned siden

    Can you do a video on 2 stroke and the effects of bore and stroke

  • Black Thunder
    Black ThunderMåned siden

    Awesome video man keep them

  • 072D00003674
    072D00003674Måned siden

    Lets build a stroker

  • Karl Jay
    Karl JayMåned siden

    No talk about the "bigger lever" of a long stroke engine? I always thought longer stroke means more torque and slower revving, so you change the gears to match the torque curve.

  • Mika
    MikaMåned siden

    Changing the stroke lenght is done by making the radius of the crankshaft bigger. That would impact on the torque the engine is putting out because of torque being force multiplied by leverage. So would´nt a long stroke engine produce more torque and therefore more power?

  • Hans
    Hans2 måneder siden

    Why not increase the valve lift for small bore?

  • hugo sepulveda
    hugo sepulveda2 måneder siden


  • n5sdm
    n5sdm2 måneder siden

    My step father worked at SWRI in the engine department. He tried explaining this to me when I was a kid when he ran the engines for this series of tests. RiP C. Wilke. 2019

  • David Libby
    David Libby2 måneder siden

    And now the question for the day is......What is the square root of "pi"?

  • something special 12095
    something special 120952 måneder siden

    So a bigger will make more hp and a longer stroke will rev up faster with less acceleration hmmm make sense

  • filthy animal
    filthy animal2 måneder siden

    Doesn't the large bore also provide more piston surface area for the pressure to act on? PSI X more SI?

    FURIOUSGAMER2 måneder siden

    Average road cars do not exceed 25m/s Koenigsegg: I’m gonna act like I didn’t hear that

  • Joshua Gibson
    Joshua Gibson2 måneder siden

    My woman says my stroke gives her more "power".

  • shadowboy813
    shadowboy8132 måneder siden

    For a given displacement, a bigger bore will exert a stronger force on the crank throw, which compensates for a shorter stroke. The reason is because as the bore gets bigger, the piston top has a larger area for combustion pressure to work on. So from a torque perspective (F x L), bore increases F, but stroke increases L. The bigger bore allows for higher revving though.

  • Aaryan Verma
    Aaryan Verma2 måneder siden

    hello sir can you plz replace our boring physics teachers, you explain very well thx

  • xsergy
    xsergy2 måneder siden

    where is the engine rpm he didnt even indicate it

  • Nathan Trost
    Nathan Trost2 måneder siden

    Very intelligent dude . All true but I wish he would of talked about engines with longer strokes having more torque

  • William Perry
    William Perry2 måneder siden

    Very good video! Many people rave about Jaguar XK120 engines. They don't know any better. The Jaguar engines were certainly not as good as MB shorter stroke six cylinder engines.

  • Rickey Daniel
    Rickey Daniel2 måneder siden

    He reminds me of Jesse from fast&furious

  • ken cohagen
    ken cohagen2 måneder siden

    What is the engine doing? Towing, four wheeling, hauling. Torque is needed and that means a longer stroke. High rpm racing engine, short stroke. The short stroke engine will rev higher, giving it higher horsepower.

  • Brad Howell-Smith
    Brad Howell-Smith2 måneder siden

    Somewhat interesting, basically covering some of the development i performed around 25 years ago.

  • Dave Wilson
    Dave Wilson2 måneder siden

    Most of the old farm tractors, IH-Farmall, Case, John Deere 270 "Johnny Pop" etc. all had long stroke and narrow bores; 2 to 1 or greater. Better for torque and lugging, pulling plows and slow driving. Very good presentation.

  • Muhammad Ali
    Muhammad Ali2 måneder siden

    Thank you for using metrics

  • Dan Kunze
    Dan Kunze2 måneder siden

    No replacement for displacement

  • Enterprise Infinite
    Enterprise Infinite2 måneder siden

    I drive a car. I watched the full length. I don't understand in the end.

  • Martin Kaufmann
    Martin Kaufmann2 måneder siden

    Piston speed: I remember in the 70ties to reed in even older technicsl literature that 17m/sec is about the limit. 60 years later we are at about 25m/sec

  • Ramp10er
    Ramp10er2 måneder siden

    Is it possible to have a 32 valves in a V4 engine to increase HP? What damage it may cause having so many valves?

  • Jeffrey Chavey
    Jeffrey Chavey2 måneder siden

    Thanks for all the great points made! But at 8:00 I am confused as the why the long stroke has a greater surface area than the one in the middle - the 86 mm bore? Isn’t surface area = 4pi times radius times 2?

  • Richard Monroe
    Richard Monroe2 måneder siden

    Seems to me a ratio of bore to stroke is most important but compression ratio is even more important while higher octane fuels would be needed at higher compression ratio.

  • Michael Nienaber
    Michael Nienaber2 måneder siden

    Bore is more important than stroke when it comes to final power output.

  • Gil Sarsale
    Gil Sarsale3 måneder siden

    how can i avail ur t-shirt..pls

  • Doug6251
    Doug62513 måneder siden

    This doesn't math out...

  • John Smith
    John Smith3 måneder siden

    So conclusion is that i'm true petrolhead cause my "stick" has high RPM performance due to stroke lenght.

  • CHEVI789
    CHEVI7893 måneder siden


  • lolitslandon
    lolitslandon3 måneder siden

    Mo powa babeh!!

  • Tim Nicholson
    Tim Nicholson3 måneder siden

    _"you do the math"_ So I've been following along on a whiteboard doing some extra calculations while you teach and at one point you mentioned maximum efficiency comes from minimizing surface area per your specified volume. Using your volume of 0.5L, I found that the optimal dimensions are in fact your 86mm x 86mm example. I'm only about halfway in so I'm not sure if you mention this but I just thought others might find the math interesting. Volume of a cylinder: V = 0.0005m^3 = π r^2 h Volume in terms of height: h = 0.0005m^3 / ( π r^2 ) Surface Area of a cylinder: SA = 2 π r^2 + 2 π r h SA = 2 π r^2 + 0.001/r Using the last equation we can find that there is a local minimum at x ≈ 0.0430127 The equation is in terms of radius so x = r r ≈ 0.043m or 43mm *d ≈ 86mm* h = 0.0005m^3 / ( π r^2 ) *h ≈ 0.086m or 86mm*

  • 114lambo
    114lambo3 måneder siden

    All your brilliant knowledge is lost with so much math for the veiwer......

  • Thomas Groover
    Thomas Groover3 måneder siden

    158 mm stroke... Lexington Steele raises eyebrow.

  • Steve Whalen
    Steve Whalen3 måneder siden

    You sir are a genius. Enough said.

  • Patrick Dufresne
    Patrick Dufresne3 måneder siden

    If Jason was my physics teacher in high school, I would have been an astronaut.

  • Iago Vitor Silveira
    Iago Vitor Silveira3 måneder siden

    I believe that longer stroke does apply more force to the crankshaft providing more torque. And I also believe that larger bores can create more forces due to the area. However, the materials applied to them need to be carefully calculated.

  • Iago Vitor Silveira

    Iago Vitor Silveira

    3 måneder siden

    If I said anything wrong please correct me. Cheers from Brazil. I really like your channel.

  • Cogar Laments
    Cogar Laments3 måneder siden

    Dr Vernon Coleman

  • Cogar Laments
    Cogar Laments3 måneder siden

    Event 201

  • Tim Ferguson
    Tim Ferguson3 måneder siden

    She wants both

  • adib z
    adib z3 måneder siden

    So, my car is 1.5 liter. But the compression ratio is 11:1, which is pretty high. So, in order for me to get more power, should i increase the intake valve cam height so the airflow can enter much higher inside my engine?

  • Tayvon Rose

    Tayvon Rose

    3 måneder siden

    @adib z don’t know what motor you have, but vvti cams are different from regular cams. Vvti have a secondary cam profile, which is why you’ll year that “vtec crossover”

  • adib z

    adib z

    3 måneder siden

    @Tayvon Rose thank you. If my cam is vvti, should i swap to any performance cam or there is vvti-compatible cam that should i swap with

  • Tayvon Rose

    Tayvon Rose

    3 måneder siden

    It makes more sense to swap ur cams out before valves

  • mbsnyderc
    mbsnyderc3 måneder siden

    You should have talked about the effect on torque the wide short stoke isn't doing to move a heavy vehicle very well. that's why you don't see it in road vehicles.

  • Paul B
    Paul B3 måneder siden

    I’ve found that there is also a trade off of torque and horsepower. As you’ve said, bigger bore/shorter stroke tends towards more horsepower but not necessarily more torque (I suppose that this has to do with the mass inertia) and that the longer stroke tends towards more torque but not more horsepower. Let me know if you have determined the same or if I’m just blowing smoke and missed the mark. Some believe torque and horsepower go hand in hand, however, my observation has been that the longer stroke provides more bottom end power - with the exception of the Mazda wankle engine - likely because horsepower is more related to rpm. Just coming from an old FAA licensed A&P mech.

  • warren hymes
    warren hymes3 måneder siden

    A longer stroke increases piston speeds all things equal. That's why we had to overhaul the older Harleys every 2 years if you used them much.

  • Andrey Zagoruyko
    Andrey Zagoruyko3 måneder siden

    Lost you on number 3

  • Wisnu Adji
    Wisnu Adji3 måneder siden

    quick question. are those stats also the same in motorcycle?

  • 2HAYLOR1
    2HAYLOR13 måneder siden

    So you just proved how the 1jzgte is better than the 2jzgte. Thank you. Been saying this for the longest

  • donnie baker
    donnie baker3 måneder siden

    NHRA Pro Stock V-Twin bore =5.125 inches ....stroke = 3.875 inches. Rpm - 10,400 rpm. Horsepower = 400

  • donnie baker
    donnie baker3 måneder siden

    Longer stroke engines are not efficient to fill the cylinder completely full of a new intake charge as the RPMs increase they also have much higher piston speed causing more friction at higher speeds short stroke engines are much more efficient with much slower piston speed and less friction and less Heat to dissipate much less wear

  • Charles Lee
    Charles Lee3 måneder siden

    Bore stoke

  • dombonagasaki
    dombonagasaki3 måneder siden

    You didn’t mention rotaries

  • Paul B

    Paul B

    3 måneder siden

    Different animal. Most people can’t wrap their mind around how the intake and exhaust works and that whole one rotation for a complete cycle thing makes them catatonic. They are more efficient but still have their down side.

  • Jay Kune
    Jay Kune3 måneder siden

    my eldest sister said, stroke is much better.

  • Paul B

    Paul B

    3 måneder siden


  • david Isaac
    david Isaac3 måneder siden

    What about dual spark config in a wide bore?

  • patrick Frawley
    patrick Frawley3 måneder siden

    With a shorter stroke, wont the expanding explosion still be trying to put pressure on the piston which will be a waste of potential energy as the piston is almost at the bottom of its stroke and so its potential work energy is going straight out of the exhaust , great for turbo charging. With the long stroke wont more of the expanding explosion potential energy be put to use, meaning wont the exhaust pressure almost be zero at the end of the piston stroke. Apart from a longer stroke giving more torque. ie Diesel engines. Surely drive-ability is the best combination of horse power and torque.

  • Paul B

    Paul B

    3 måneder siden

    Only at lower rpm. When they both get into their design operating rpm it’s pretty much as he described with the operating range of the long stroke lower than the operating range of the over bore.

  • lelouch britannia
    lelouch britannia3 måneder siden

    So if i increase bore.. Does my low rpm will downgrade

  • HM51
    HM513 måneder siden

    Question: What limits piston speed to 25 m/s? What changes would allow this to go higher?

  • Paul B

    Paul B

    3 måneder siden

    Inertial mass. Shorter stroke has lower inertial mass so there’s less to overcome when pistons and piston journals change direction.

  • Raymond Garafano
    Raymond Garafano3 måneder siden

    The way I always understood it, if u want more torque you have a longer stroke ( the farther away from the crankshaft you go the more torque is on the crankshaft, but for lots of power at high speed a big bore w short stroke.

  • Raymond Garafano

    Raymond Garafano

    3 måneder siden

    @Paul B EMD's 567 engine is a 16 cyl. job with close to a 10 in bore and stroke. used on locomotives rated over 1751 hp.

  • Paul B

    Paul B

    3 måneder siden

    That’s correct

  • T Mo
    T Mo3 måneder siden

    There IS a difference between cm^2 and x(^ 2)CM. Centimeters squared vs squared centimeters. YOU ARE AMERICAN. SORRY.

  • T Mo

    T Mo

    3 måneder siden

    Could we get this right for the next generation. ...¿

  • Phillip Brown
    Phillip Brown4 måneder siden

    Can anyone tell me can I get more h.p with a bigger piston compared to smaller piston with the same flat top on both pistons

  • William Apodaca
    William Apodaca4 måneder siden

    What's up with the dagger on the crank of that cutaway

  • Mark Robinson
    Mark Robinson4 måneder siden

    Huh? Hard to believe you squeezed that into 15 min and I do appreciate the technical "no free lunch" break down.

  • Mahmood Bello
    Mahmood Bello4 måneder siden

    This was very insightful on various fronts.

  • Sean Kennedy
    Sean Kennedy4 måneder siden

    Holy hell this is complicated, is this what car companies deal with?? As an end user / consumer I’m in awe; thank you VW for dealing with all this and giving me a great car to drive 🇺🇸❤️🇺🇸

  • James owens
    James owens4 måneder siden

    Why do I feel like he’s never turned a wrench in his life

  • Paul B

    Paul B

    3 måneder siden

    Because he likely hasn’t.

  • Tom Preble
    Tom Preble4 måneder siden

    As I age, I strive to continue being an undersquare guy: Bore (waist belt size =33) Stroke (inseam = 36) Better torque is key! ; )

  • Paul B

    Paul B

    3 måneder siden

    That’s funny 😆 Me, I’m over square. Bore larger than stroke.

  • 1crazypj
    1crazypj4 måneder siden

    I'm a motorcycle mechanic so not trainedin engineering or engine design but I've done a lot of reading over the years. Doesn't connecting rod length have an effect on piston acceleration, side loading and when maximum torque is developed?( rpm) Burn time is relatively fixed which is why ignition has an advance curve to start burn BTDC with maximum pressure somewhere around 14 degrees ATDC. Unless a manufacturer is designing a totally new engine, 'ordinary people' are looking for ways to maximise what they already have , bigger bore generally being the cheapest and easiest but with limitations on maximum bore size due to cylinder spacing. The largest overbore I've ever done was 14mm which actually utilised the oversize ports way better than the manufacturer (1970's designs, big ports, high cfm, low gas speed)

  • D. S
    D. S4 måneder siden

    seems like the smaller bore would reduce detonation and increase the burn rate, but also have more reciprocating mass which evolves in higher energy, but you would want a bigger bore for better volumetric efficiency, depending upon using naturally aspirated or forced induction, or even the type of fuel being used, or whether you need a high R.P.M. application or not. What to do... what to do?