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Author Topic: Are motorcycle engines more efficient?  (Read 2387 times)

Offline bcou

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Are motorcycle engines more efficient?
« on: 14/01/2014 14:22:32 »
how are motorcycle engine way more efficient than car engines ?


 

Offline CliffordK

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Re: Engine efficiency
« Reply #1 on: 14/01/2014 14:55:27 »
It would depend on how you define "efficiency".

As far as fuel efficiency, I don't think they are more efficient than car engines.  However, the average motorcycle weighs only a fraction of the weight of the average car, and also has a smaller frontal profile causing less wind resistance.  Thus, one typically gets better overall fuel efficiency for the vehicle.

I'm not sure about energy density.  One can tune a car engine to give better than 1 hp per cubic inch displacement, perhaps upwards towards 2 hp per cubic inch (100 hp per liter)?

Anyway, there is a trade off between fuel efficiency and motor longevity, and tuning.  With cars, the decision has been to make larger, heavier engines with less power and better efficiency.  With motorcycles, on the other hand, the power to weight ration is extremely important, and thus engines are tuned for more power at the expense of fuel efficiency.

Air cooled engines may be lighter than water cooled engines, but are often less efficient.

Peak HP is often at higher RPMs.  Do Motorcycles run at higher RPMs than cars?  Some older motorcycles may use 2 cycle engines (twice as many power strokes), although I don't think they are very common now.
 

Offline syhprum

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Re: Engine efficiency
« Reply #2 on: 14/01/2014 16:28:29 »
In Europe were 97 octane fuel is normally available the trend seems to be to use smaller engines with turbo chargers such as the latest Jaguars and BMW,s with specific outputs of 2 BHP per cubic inch with presumably less weight and higher effective expansion ratios.
With more room available for fancy electronics and variable valve timing etc on the basis of actual thermal efficiency the best car engines probably exceed those of motor cycles and I think the oft stated figure of 30% is an understatement
 

Offline alancalverd

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Re: Engine efficiency
« Reply #3 on: 14/01/2014 17:31:52 »
In Formula 1, if an engine lasts more than one race, it's heavier than it needs to be. In a light aircraft, 0.5 HP/cu in is normal because engine failure means losing a lot more than a race and you cruise at 75% of max power compared with 25% or less for a road car.
 

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Re: Engine efficiency
« Reply #3 on: 14/01/2014 17:31:52 »

 

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