Team-BHP
(
https://www.team-bhp.com/forum/)
800 cc bike is exotic, it's a super bike, 800 cc car is entry level, FE is the last thing on a guy buying 800 cc bike, he wants to experience thrill, fun and smile every time he takes the bike out, damn be FE.
If someone asks me bhai aapki bike kitna deti hai, I respond
"maza deti hai" and ride away.
:p
Valid question and I gave been asked similar questions on why a motorcycle engine of the same cc is more powerful. My understanding is as follows and happy to learn more
Considering normally aspirated engines for comparison sake, I would believe that a motorcycle cycle engine would develop similar torque as a car engine of the same (say, 800) cc. The motorcycle engine revs higher and develops correspondingly more bhp and pips the car for power to weight ratio and hence acceleration.
Depending on the bore x stroke aspects of engine design, the car engine might have better low end torque with a weaker top end and vice versa for the motorcycle. This could impact fuel efficiency experienced during everyday driving cycles
I get your point, and although people have made some solid points/arguments, none have been particularly convincing so this brought me out of my usual reading from outside to actually logging in and trying to add my 2 cents to this topic.
I’am as curious as you are and have wondered the same from time to time, the reply can’t be simple or generalised as it varies from engine to engine, i don’t think the motorcycles are less fuel efficient than a similarly sized car engine just because they are faster and not designed for maximum efficiency, motorcycles come in all shapes and sizes and some of them are just plain outdated and so they are neither fast nor fuel efficient, atleast relatively.
Now, take for example Royal Enfield, i’m talking about the 350cc and 500cc here, if you were to compare its power and efficiency ratio to a car engine, you will have to bring engines from ancient ambassadors and padminis to make it an even playground, because these engines hail from an era which is even older than the ambassador, now granted they have been updated in late 90s and late 00s but they still are about as simple or outdated as it can be.
Same case with some other bikes that you are comparing, they are inefficient because they are older and technologically inferior than even the trusted Maruti 800cc, this is why it makes no sense that they have similar power yet lower mileage despite having to haul much lower weight.
Now if you consider a relatively modern bike engine, even if it is designed for speed, it will be substantially fuel efficient with respect to its power because a great engine is always an all rounder, otherwise its a plain bad engine design. Take for example Creta’s 1.6 Diesel, it is a a gem of an engine because it is fast, punchy yet fuel efficient at the same time.
I also ride a R15 v3, and it revvs till 11000 rpm, now i ride it enthusiastically and the engine itself is build for maximum power in its class (150cc), yet since it is relatively modern (liquid cooling, Variable Valve Actuation, Fuel injection), it still returns a stellar fuel efficiency of around 50kmpl in conditions where a similarly powerful and somewhat as technically modern Swift (the 0-100 timings are in a similar ballpark although the Swift should be faster post that speed and also has a higher top speed) would return about 12kmpl, because it has to haul much higher weight and also has to power the hvac system and other electronics.
But if you want a CC to CC comparison in modern engines, then yes a similarly sized bike engine is usually (in case of sports bikes) tuned for much more peak power and a 1200cc sports bike would be as fast as a Ferrari and the power would be much higher than a swift and naturally the fuel efficiency would be lower.
So if you have make sense of things take it this way,
If you want a similar performance as a car, you would need a much smaller capacity bike and the smaller displacement and much lower weight would result in an equal and proportional increase in fuel efficiency (assuming that both engines are modern and from the same era)
If you compare a similar CC bike engine then the modern bike engine you find will be much more powerful than the car engine and that combined with lower weight the bike would be way faster, so it would be pointless to compare the fuel efficiency.
If you do find a similar CC bike engine and the power is similar too, chances are it is an outdated engine which uses decades old technology and that is why it is nowhere as powerful/efficient as it should be. The exception here could be cruisers, they have more torque lower down and generally less power, their power can be compared to similarly sized car engines and provided that cruiser bike has a modern engine, which is built for more lower down torque (much like a car engine) and doesn’t revv to crazy high RPMs, there is no reason why it should not be more fuel efficient than the car because of its substantially lower weight, and less engine load, but if it is not, then it is safe to say it is not a well designed engine, as simple as that.
Hope this helps.
Quote:
Originally Posted by sajaijayan
(Post 4698780)
I am not aware if this discussion has happened before, however, have always had this question and never really got an satisfactory answer. Best place to ask is this fantastic forum of absolutely knowledgable people, so here goes
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Thought of writing an explanation but had a rethink.. Most of the reasoning has already been provided and the info is already at your fingertips courtesy of Google :D
Quote:
Originally Posted by srini1785
(Post 4700969)
A thought experiment question:
What would happen if you plonk a Alto 800 engine into a motorcycle frame?.
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Won't be the first time someone has thought of it. Also these people realized if they're gonna do it, then why stop at small capacity? Why not a 8L V10? And the end result was the Dodge Tomahawk! clap:
Anyone have any figures for specific fuel consumption?
Road speed at 1000RPM for the various gears?
Any thoughts on wear/ life of engine?
Regards
Sutripta
The comparison itself is flawed. The bike will give much better fuel economy than the car. A 800 cc Alto can at best give 15/17kmpl if driven normally (ac on and two people, with speeds up to 100kmph). A 650cc twin (Versys) will return 25+kmpl under the same conditions. To get the Alto's fuel economy the Versys will do in excess of 160/170kmph with two up.
It is a very relevant question, unlike what other members have posted above w.r.t meant for speed v/s meant for efficiency ; driven agressively v/s driven sedately etc.
I am 100% sure, a high performance 1200CC bike will be more efficient than a commuter car like swift with its 1200CC kappa engine ; if driven in the same way. Only thing is, the bike has a wide range of 'aggressivity range' from 'very gently' to 'extreme racing'.
The scientific answer will account for all these factors :
1) longer stroke small bore in car v/s short stroke bigger bore in bike
2) brake specific fuel consumption (BSFC) at different operating points. The bike engine has a much wider range of operating points than the car.
3) gear ratios
4) of course, weight
The internal combustion engine is, by nature, a non-linear energy dissipation device ; hence the answer is not as straightforward as any one of the four reasons above, but a combination of all four.
Few cents from my side.
- 800cc car will produce less than half the power of an 800cc, will have less complicated construction, conservative gear ratios, hence cost would be very much less. R&D too would be hugely different, hence cheaper for the car.
- Entry level car would sell at least 20K units a month, while an 800cc bike wouldn't sell more than 1k units a year. Economies of scale comes into play here.
- Apart from weight, power, cubic capacity, FE also depends on gearing and way power is delivered, theoretically it would be possible to make a high capacity motorcycle will 40+ km/liter but no one would do it as the whole point of these bikes are about performance.
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