Comparing Horsepower per Liter in Motorcycles

Horsepower per liter comparisonsJames Parker has an interesting comparison of horsepower per liter among several different motorcycles in the March issue of Motorcyclist. It's not a difficult calculation but I seldom think about it, though I may think about it more after reading these numbers.

According to Parker, the 800cc MotoGP bikes are making about 240 horsepower or 300 hp per liter, pretty high output for so little displacement, it reminds me of what the Formula One race cars are doing, small engines with ridiculous power. The B-King tested in the current issue was about 120 per liter, the V-Max about 101. Buells and Ducatis come in around 85 per liter. Sliding down to the low end of the scale, the Royal Enfield 500cc puts out 22 horsepower or 44 per liter. He points out, however, that the Harley Davidson Cross Bones they tested with its 1584cc 70 horsepower engine, also comes in at 44 per liter. The Victory KingPin bests it by a tiny bit at 46. Of course, the Harley is a big engine so it still has a lot more power than the Royal Enfield but from a pure efficiency standpoint, it's in the same spot. Sort of shows that a large, air cooled, pushrod, 2 valve engine has limitations.

Now, before someone starts making remarks about Harleys, just remember, efficiency is interesting and shows us how well the engines use the displacement they have but the actual horsepower and torque are what make the performance difference. Unless you are racing in a displacement defined class, efficiency, in a street bike, isn't that important. Need more power, just go bigger, adjust size until you get what you need.

Comparisons like this are interesting for the tech oriented motorhead, but as soon as you start down this road the bragging rights crowd starts playing the "mine is bigger" game, even though it doesn't mean much on the street. It does get me thinking though, ... we need a chart! I may have to get some numbers together.

Comments

  1. Chris says

    Although there’s no “replacement for displacement”, that really only applies to torque. Remember that horsepower is all developed in the cylinder head. If you build the engine with lightweight internals (to rev higher) and a free flowing cylinder head(s), you will undoubtedly turn a rather low-powered engine into a much improved one, although obviously there are limits to this.

  2. 64chevyman says

    It’s also interesting efficiency isn’t the fuel efficiency. That surprisingly is high in big v twins. Unlike big V-8 engines not matter what you do it still is lousy. Why is that a big v twin gets relatively good mileage. I had a 63 289 Ford F150 that got good mileage and ran like a top! Go figure!

  3. Tin Man 2 says

    Durability is also an issue, A lower stressed engine is as a rule a reliable long term unit. An F-1 engine would not hold up to street use and many high output street engines are finicey and labor intensive.

  4. RGVyan says

    I find horses per ton a more revealing figure. Higher displacements may produce more power but they also have to sacrifice a portion of that in lugging along extra weight.

  5. BillyB says

    And keep in mind rideability and mileage are issues for many high-horsepower bikes as well. If you don’t need snappy throttle response, I’m sure many of the “inefficient” bikes are easier to ride. That said, the new V-Max is actually very civilized under 5000 rpm, but then it gets under 30 mph. The “inefficient” 44 hpl Harley can get 50ish mpg on the highway if you’re just cruisin.

  6. kneeslider says

    If you look at 2 strokes, the ratings can be impressive. The TSS RS500 puts out 112 hp or 224 per liter!

    Top fuel engines of any sort do get crazy numbers but I don’t think of them as running, their short duration between rebuilds seems more of a semi controlled slow motion explosion, it doesn’t count. At least MotoGP or Formula One engines can run for a while.

  7. says

    Wow, 300hp/liter! Amazing, of course there are compromises to be made but I love to think about the extreme “what if” scenarios. 300hp/ltr, hmm maybe a 125cc motorcycle with 37hp..wait, why does that sound familiar? oh yeah, 2-strokes! It seems small displacement bikes have a lot more incentive to increase efficiency. Ok, on the other end of the scale there is a 1300cc 400hp street bike with 300hp/ltr? Hmm, turbo Busa’ might fit the bill.. How about the “outer limits”? A triumph RocketIII 2.3ltr with 300hp/ltr works out to 690hp! I’ll take two! Of course if torque curves are considered, The outlook is a bit more realistic, not to mention engine longevity but it’s interesting to look at whats possible and whats available. Thanks Paul for this thought provoking article.

  8. Wave says

    Well, if you look at the world of drag-racing motorcycles then the specific power outputs start getting really silly. Jay Upton is a famous front-runner in Top Bike here in Australia, and his Honda-based supercharged bike (which is completely custom made and does not use ANY factory Honda parts) puts out roughly 1600hp from it’s 1600cc, giving it 1000hp/litre! Awesome machine, but as stated previously by some, at this power level the engine suffers durability issues with running hard for more than 10 seconds!

  9. says

    Hello Paul –

    One engine that would be cool to add to the chart would be the Irving Vincent air-cooled pushrod from Australia.

    They are working on a 4-valve head for their racebike that may be run at this year’s Daytona. This engine has dyno’d at 180 hp and 140 ft lbs. of torque.

    Understandably, this is a race engine and not to be compared directly to HD’s air-cooled pushrod engine.

    Maybe they will chime in here about their road-going version? (this could be my all-time favorite bike)

  10. Walt says

    You’re right, Paul — this is important for racers and techno theorists, but irrelevant for most riders. On the street or trail having enough power where you need it in the RPM band, together with good mileage, is all that really matters. Whether you get the performance you want from a high-strung 600 four, an OHC twin or a pushrod porker is a matter of different strokes for different folks. For me it’s a 955cc Triumph triple that delivers good midrange and 50+ mpg.

  11. Jeff says

    That’s why I like my stock 06 Buell XB12R so much . Low RPM gobs of torque for the street as opposed to my old Yam FZR 400 racer high strung as hell had to stay at least 10 grand all the way to 15 grand on the rpms just to stay in the power band but what a hoot .

  12. Phoebe says

    Thanks, Hoyt…that’s what I thought it was, but I wasn’t sure. It’s uh…not exactly the belle of the ball as far as engines go…

  13. Mike says

    HP/Liter is one of many methods of determining efficiency, however BMEP (brake mean effective pressure) is still a more accurate number, as it accounts for things such as displacement, torque, RPM etc. It doesn’t however, account for feel, and like most of us, we want a seat of the pants rush.

  14. Schneegz says

    “…actual horsepower and torque are what make the performance difference. Unless you are racing in a displacement defined class, efficiency, in a street bike, isn’t that important.”

    I disagree. Bigger displacement usually means more weight. You may not need a feather-light bike for the street, but the handling difference between a 650lb cruiser and a 450lb standard is substantial. Weight also affects straight line performance. Give a bike a big, heavy, inefficient engine and you have to make the bike heavier to handle the weight of the engine. You then require more horsepower to make the bike accelerate the way you want it to, so you make the engine bigger, which also makes it heavier, which makes the bike heavier, etc.

    I’d much rather ride a relatively light, efficient, sweet-handling bike than a two-wheeled barge that only feels right going in a straight line (if that).

  15. motronic says

    Horsepower per liter is a dumb metric. Same lamness that’s talked about in the ricer/euro vs. American performace conversations. You’re just comparing design philosophys. Horsepower per unit of fuel consumed is “efficiency”. The physical mass and volume of engine compared to horsepower made, is something else, “dimensional efficiency” maybe?

  16. theduded says

    It seems the other major chartable measure of efficiency is only mentioned here. Side by side with the horsepower per liter charts should be torque output per liter. With these you can start to gain a better understanding of the engine’s efficiencies.

    Without torque numbers the calculations are only trivial. Put a super horsepower output F-1 engine in something big and run it around and see what all that horsepower is good for (high reving top end output).

  17. todd says

    torque per liter won’t get you very far, it leaves out crucial information like rate. A bike with 50 lb/ft at 2500 rpm is exactly half as powerful as another bike that puts out 50 lb/ft at 5000 rpm. Then the deficit is compounded by the fact that the 2500 RPM motor must be geared much higher to achieve satisfactory (comparable) road speeds.

    Horsepower charts take all this in consideration. It takes approximately the same amount of HP to go a certain speed from bike to bike. No matter how much power your bike is rated at or how fast or slow the engine is spinning it’s only putting out, say, 20 HP to go 80 MPH on the freeway – regardless of how much you and the bike weigh. Weight is the factor that will help determine how fast you accelerate. This is where horsepower per pound charts come in handy. A F-1 engine would last forever on the street where it’s required to put out only a fraction of its maximum.

    Then there’s wheelbase, weight distribution, and traction.

    Fuel efficiency is mostly determined by how closely and how often your engine remains at or near peak torque output (peak thermal efficiency). Larger, low revving engines are geared higher therefore requiring more throttle putting the engine closer to max torque at speed. A high HP bike in 6th gear is well below its max torque output (RPM, throttle opening) on the highway. A low HP bike like a Harley is much closer to max output in top gear on the highway.

    Then there’s aerodynamics…

    -todd

  18. ep says

    @motronic

    I wouldn’t say power/displacement is a dumb stat at all. Maybe it’s applied in ways that don’t make sense by people who don’t always know what they’re talking about. You’re referring to someone, for example, who says an S2000 is technologically superior to a GTO because of the HP/litre differences, and in that respect, yeah it’s not that useful. The goat wins on shear brute force, regardless of how it’s designed. But if you’re limited in your displacement, i.e. 800cc motogp bikes hp/litre matters quite a bit and therefore low compression, pushrods and 2 valve heads become less attractive.

  19. hipsabad says

    MotoGp at 300hp per liter. Hmm, let’s see, the current one-liter sportbikes put out approximately 180 per liter. Wait, it gets even better: the latest crop of 600 sportbikes, an R6 for example, put out approximately 200 HP per liter. The 2007 CBR600RR weighs only 350 lbs. dry and 412 lbs. fully gassed up ready to ride. Impressive performance to be had for only several thousand dollars. If that’s your thing, it’s a good time to be alive.

  20. Tin Man 2 says

    There is no secret to making HP, the Tech has been around for almost 100 years. The 1910 Peugot French Indy racing cars had 4 valve heads with double overhead cams, Incedently we stole this Tech for the design of the Novi Offenhauser engines that rulled Indy for 60 yrs. Modern designers have a choice of engine characterists, Its not rocket science the heavy lifting was done long ago. If one company decides to offer more power its not hard to do, If another builds slow reving Torque motors it is by choice to appeal to people who want low down power. There is no right or wrong, There is no correct answer. Every design is a compromise, The current use of adjustable Cam Timing is an effort to narrow the comprimise between Torque and HP. Its not NEW the knowelge has been around for ever, The price people are willing to pay for Tech is what is new.

  21. says

    How is HP/L a useful comparison method, again? My CBR125R and VTR250 put out 106.4 and 128, respectively, which means that they’re hugely better than everything except the superbike, right?

  22. paulinator says

    The link to the 3 banger 50 cc Suzuki with a 14 speed gearbox paints a picture. The engine is but one component in the system. Paul, can you develop a graph that plots available rear-wheel torque over a speed range (say 0 to 200km/h)?

    I was just asking…

  23. Wisedog says

    wow.. then my little 150cc bike is in the same level as V-Max? 120HP/L with top speed around 70mph and can do 70 MPG? off course in my country, U’ll get more attention if riding V-Max :)

  24. John says

    Todd, reading through your post was mostly bla,bla,bla, until I saw that you stated a formula one motor would last forever on the street.Have you ever watched a formula one race?They have to rev those things to 10 grand just to get them moving and they still stall them all the time.One of those would be the biggest piece of worthless crap and most time consuming with maintenance machines I can imagine.I would love to drive something like that but for the street an understessed big inch slow turning motor is the way to go.

  25. Tin Man 2 says

    Todd, You have some misconceptions about Torque/HP. I drove a Tractor trailer for 32 yrs so I know some thing about power. Our big rigs had only 300HP but 750 Lbs of torque at 1200 RPMs, this was designed in, not an acident. Long lasting Fuel efficent power is formost in mind for commercial buyers. For racing you want HP, for street use Torque is what matters. Your comments about 50 ft lbs at diff RPM levals is simply NOT true. Higher RPM increase HP, That is easy to do and works for racing BUT you are comparing Apples to Oranges . 50 FtLBs is 50 Ft LBs at any RPM, the cross over point for engines is 5250 RPMs for the artificial concept of HP, not 5000 RPMs.

  26. motronic says

    @ everybody
    What about efficiency being a certain amount of input (air & fuel) giving a certain output (horsepower or watts)?

    Higher rpm is artificial displacement, bringing in more mixture with revs rather than swept volume. 4000 rpm 6 liter, moves the about the same volume of mixture as an 8000 rpm 3 liter.

  27. todd says

    Torque is a measure of force, horsepower is a measure of work. You need to put in force to get work done. You measure work by how long it takes to do it.

    Some people can move a bus with their teeth. That same bus also has an engine that can move it along too. Does that mean that person has as much power as the bus engine? No, we need to consider how long it takes to move it. I don’t know what you’re trying to say about “cross over” RPM. The 5250 number you mention (actually 5252) is the result of the horsepower calculation : 1 HP = 33,000 foot pounds per minute, then 33,000fp/m divided by 6.2832 (the distance around a 1 foot radius circle) = 5252. That number then becomes the denominator in the equation : (Torque X RPM) / 5252 = Horsepower. I understand Torque/HP completely.

    The amount of work your rig was doing at full throttle/load was 300HP (actually 223,800 watts). You could theoretically drive the same truck down the road at the same speed with 1 foot pound of torque but the engine would have to spin 1,575,600 RPM to do it. In order to keep the engine life long they design in more torque to keep the revs down. Besides, diesel doesn’t burn quick enough for high RPMs. Remember, even a good bicyclist can put out around 150 foot pounds of torque.

    I think people have some misconceptions about racing. Wherever there is horsepower there is the same ratio of torque and RPM. Formula 1 cars burn clutches and stall because they are essentially starting out in third gear. That F-1 engine still makes much more torque at nearly every RPM than your average V-8. All the exotic materials that go into those motors definitely make them much more durable under street conditions than anything else out there.

    All torque and horsepower measurements (dyno runs) are done at full throttle, full load – a condition that is rarely achieved in real life, a little more often in racing. Every car going down the road at the same speed is putting out roughly the same horsepower.

    -todd (bla,bla,bla)

  28. John says

    So buy a formula one motor and put it in your pickup, I’m sure you’ll be very happy with how it works out for you.

  29. says

    great article, and i completely agree that this stat is absoloutley meaningless on the street(really not that useful on the track either, compared to power to weight). it pains me every time some BMW or honduh driver(cars, not bikes) brings up HP/liter comparisons to an american V8, because it means utterly nothing! give me a GM 6.2l LS3 all aluminum push rod V8 any day over the BMW 3.0l I6, since the engines are almost equal in weight. better yet, give me a light weight turbocharged anything and i’ll be happy!

    BTW, ive been wondering for the longest time why low displacement forced induction engines havn’t caught on with bike manufactuers. its really beginning to take hold in the automotive world, direct injection too. i just dont see the disadvantages out weighing the advantages. this is a discussion for another time though. maybe an article exploring this, paul?

  30. Brent says

    Todd is right. Torque is a meaningless parameter. Why? Because it’s what happens at the rear wheel that counts and you can make the rear wheel torque anything you want. All you have to do is select the gearing. But whatever gearing you select the power will be the same (minus small losses due to friction). At any given road speed, my 60hp Aprilia RS250 produces more thrust at the rear wheel than my friends 50hp Harley even though it produces less than half the torque. The down side is I have to shift gears more to stay in the 8000 to 12000rpm power band. It’s generally assumed that a high winding engine will have a “peaky” power band. But even that ain’t necessarily so.

    The Harley makes about 55ft*lb of torque. Compare that to a bike that makes 42ft*lb. You’d assume the latter would provide less performance. But that’s what Jay Leno’s gas turbine bike engine makes at ZERO rpm. At it’s power peak it makes on 20ft*lb. But it makes 330hp because that 20ft*lb of torque is at 35,000rpm. Now you may say that is a meaningless comparison because the turbine is geared down to deliver a lot of torque at the rear wheel. But that’s exactly the point. The 330hp vs 50hp does really reflect performance. The 55ft*lb vs 20ft*lb is meaningless.

  31. Nicolas says

    So, we’d need a scale that would be :
    rear wheel thrust per mph per displacement per bike’s weight per mpg per $$ …

    (of course $$ would be total possession costs, purchase + maintenance + insurance – resale value)

    What about a scale to measure the length of the grin on the rider’s face ?

  32. Kenny says

    @Brent
    I agree with you, but on the subject of torque i must beg to differ.
    In a purely theoretical setting your argument that torque is a neglible statistic would be pretty solid argument.
    Unfortunately, as any engineer knows all to well, we do not live in a theoretical world and we have to deal with the limits of the real world. Theoretically it is possible to make a 50cc IC engine rev to infinite, or gear it to break every landspeed record ever, but we simply cant.
    The reason why 50cc engines aren’t as popular as larger engines is because it takes forever to get up to speed, you could theoretically use a cvt to get similar performance as a larger bike but realistically there are size and weight restraints.
    This is where torque comes into play. The torque output of an engine(at the crank) is pretty much constant, determined mainly by displacement and stroke.
    This “constant” torque allows us to take shortcuts, less extreme gearing and so on.

  33. todd says

    50 ft-lb of torque at 2500 RPM = 24 HP. 50 ft-lb of torque at 5000 RPM = 48 HP. A 48 HP motorcycle is twice as powerful as a 24 HP motorcycle. Ironically they both produce 50 ft-lb of torque. You can gear the second motor 50% lower than the first for the same road speed and shifting intervals giving you twice as much torque at the rear wheel (thrust). Sure these are theoretical engines but why is this so hard to understand?

    -todd

  34. Kenny says

    I agree with you too todd, your preaching to the converted here. I guess what i was trying to say was that its a lot easier(and more usefull) to get an engine to produce power by getting more torque out of it(by increasing displacement or messing with the stroke or forced induction), than it is to try and get the engine to spin up to some crazy rpm.
    Sorry if my previous post was confusing i’m looking back at it here and realised i never made a point myself.

  35. Patik says

    Its true that HP is a better messurment than tourqe. But just top HP doesent say much. The first time I drove a 120 HP 600cc I was beaten at the traffic lights by an old rusty volvo 240 with a crack-head behind the wheel. I gave gas, shifted and gave gas just like I was used to. Turns out that I needed to alway keep the revs up to be able get something more than 26 HP – or whatever it could produce within the normal driving range of rpms. Fun for a while but nothing for me. sure, I want 120 HP but I also want em to be present at a twist of the trottle, not 3 gears down. And for that you will need a bigger engine or supercharging/turbo.

    TODD was talking about gearing; well thats absolutley true if you hook it up to a generator, for example in a hybrid car. But in real life you drive engines from idle up to valve float/rev limiter. Your 48hp engine ARE twice as powerful at peak power, but at 2500 rpm? at 3000 rpm? ideling carefully thru town? At all the other rpms?

  36. Patik says

    Ps to get all facts straight, at least I wants to know, tourqe, hp and on what rpms they are present. I also wants to know how big the engine is and how heavy the bike is.

  37. James says

    something wrong here.. from the article “He points out, however, that the Harley Davidson Cross Bones they tested with its 1584cc 70 horsepower engine, also comes in at 44 per liter. The Victory KingPin bests it by a tiny bit at 46. Of course, the Harley is a big engine so it still has a lot more power than the Royal Enfield but from a pure efficiency standpoint, it’s in the same spot. Sort of shows that a large, air cooled, pushrod, 2 valve engine has limitations.” A, as shown by the article Buell’s are at 85 hp/liter they are air cooled pushrod two valve engines, B. efficiency standpoint in and ic engine would be Hp/mpg the horsepower/engine displacement ratio is a moot point, take a Stirling engine most of them are somewhere around 4-6 hp/liter but at a 80-90% efficiency…… so how fast does your gallon of gas get you?? that’s the million dollar question! (side note does anyone know the hp/liter of the xr750? that out to tell all of us the limits of air cooled better then anything else!)

  38. todd says

    The XR750 had 90HP @ 8000 RPM (so that’s 59 lb/ft BTW). That’s 120 hp/liter – without the rider…

    BTW, I don’t ride according to what RPM the engine is at, I ride where the bike is making appropriate power for the road I am on and whether or not I need to accelerate hard or I’m slowing down. I never understood this fascination with low RPMs. Cruising down the residential road on my R75 is around 3,000 RPM. On my 90cc Yamaha twin it’s something like 8,000 RPM. I would never try to lug the yamaha down to 2500 RPM just because that’s how I ride the BMW. Engines need to rev, that’s where they are efficient, that’s how they live long, happy lives.

    -todd

  39. James says

    there you have it 120 hp per liter, not bad at all! it’s no wonder they are still racing those old things. wouldn’t be nice if Harley had stayed on the racing game? Or better yet if they had released say the xrtt 750’s on the poor public of the 70’s? Oh well no point in dreaming…. Need to be building!