Just out of curiosity-and perhaps slight ignorance-how does a bike engine work?Is it the same as a car combustion engine, and if so how does an engine that small produce so much power,and why is it so small?Any explanation would be great!

Yes they work in exactly the same way.

The power comes from the fact that they are more highly tuned than your average car engine and the fact that they rev to nearly twice the limit of your average car engine.

Small, because they have to fit on a bike

Yes a bike engine is the same as a car engine, but made of more exotic materials so that it can turn faster.

A simplified way of thinking about it is that any engine is just an air pump really, with a tiny amount of fuel added to the air. The faster the engine turns, the more air it can displace and the more power it can make. So a 1 litre engine turning at 12krpm could make the same power as a 2 litre engine turning at 6k rpm.

It's exactly the same as a car engine. That being internal combustion.

However, they are made to go on motor cycles. They are therefore made as light as possible. Imagine having a 450Kg lump of iron strapped under your bike and trying to stand up at traffic lights....

So right from the start motor cycle engines had to be light.

They also had to be able to have the gears sequential because you couldn't use your hands to change gear like on a car so each cog was selected by the same movement (OK one down 4 up but esentially all in the same direction)

Then the power... They are engineered very well. Will usually rev much higher than a car engine with the same capacity. Usually up to 12000 revs.

All this combined gives the bike engine the edge when fitted into a small light car like a 7 replica.

Power to Weight.

With the added of a close ratio siquential box....

Recipie for madness.

If it's four stroke it's the same as a car. If it's two stroke the piston also acts as a valve.

This really is a fascinating subject and I'd recommend a good book or perhaps cheaper and easier a bit of web searching on "internal combusion engines" or "Two Stroke Engines" etc. should keep you busy for a good few hours.

Remeber that necessity drives design, can you imagine wobbling down the road with a pinto and mt75 under your arse

remember a lot of bikes have less than 4 pistons aswell

we used to own a ccm 620 supermoto fitted with a rotax engine and it was one piston

you wil never hear anything as good or feel something that delivers its power so fearce in 5th gear

imho its because they use a much higher compression ratio on a smaller engine that is built with tighter tolerances and therefor revs higher that they can produce the power they do for such a small capacity lightweight unit.

Ned.

No mention of Torque?

Presumably this is why all our tintops still have around 2.0 sized engines that only go to 6K rather than 1.0's that go to 12K.

quote:

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Originally posted by pajsh
No mention of Torque?

Presumably this is why all our tintops still have around 2.0 sized engines that only go to 6K rather than 1.0's that go to 12K.

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Many thanks-mainly curiosity,but am quite tempted to read into it more-though seems I have all the answers here!

Wonna know how engines work? Well How Stuff Works usually has the answer and some cool stuff too!

power = torque times revs. A bike engine revs twice as high as a car engine and so makes twice the power, if the torques are the same. Bike enignes are more highly tuned and so a 1000cc bike engine will have a bit more torque than a 1000cc car engine and so therefore more power.

Car engines generally have lazy tunes and so can be tuned by porting, skiming the head and changing the cam. This is already build into the design of a big bike block.

Normal road car engnines have to be in low states of tune and have heavy (inertia giving - but max rpm sapping) internal components to give the drive that most drivers require. Imagine your Mum popping down the shops using only 6000rpm through the gears in her fiesta. It would freak her out. Saying that, my Mum would probably be up to the limiter, whatever the limit was!

dmottaway has the best explanation on this subject so far. Torque is like a tightening a nut with a spanner. The spanner being the crankshaft size. A large spanner will create a lot of force on the nut but will not be able to rotate very fast. A smaller spanner with the same amount of force on it will not create as much torque but will be able to turn faster and therefore the horsepower figures will be high. Generally bikes sacrifice torque favouring horsepower as the bikes dont weigh that much, and high revs are desirable so that one gear will have a large speed range. eg honda hornet 600cc 2nd gear will start around 5mph and will end up at around 95mph. However off road four strokes will often have few cylinders, two at most. This is so that the crankshaft has a large throw hence high torque low revs. Fast acceleration can be acheived but constant changing of gears is neccesary. Top speed generally is quite limited. As far as materials are concerned aluminium is used alot due to its weight properties.

I thought you just twisted the grip and it goes brummm

Torque decides how fast you will go...

BHP determines how exciting getting there will be...