1) Why can motorbike engines rev so high? Presumably it’s the sports bike ones – are they two cylinder ones?

2) When I hear people rev them up, the revs seem to go up and down very fast, is that cos of the lower mass of the moving parts or what?

3) What kind of stroke/bore do they have? Presumably this contributes to high revving?

4) Why aren’t they turbocharged? That’d give more power for smaller physical size, surely?

Tell me about motorbike engines please.

1. Shorter stroke usually means higher reving as there is less mass to reciprocate – most high reving sports bikes are generally 4 cylinders.
2. Yes
3. Have a look at manufacturers websites for exact details good example here http://en.wikipedia.org/wiki/Yamaha_R1
4. Cost & lack of linearaity (you don’t want a powerful bike to ‘come on boost’ mid corner whilst still leant over) although turbos are becoming better at smoother power delivery.

1+2 – Essentially right also because the require less torque than say a car engine of the same capacity they can chase for power I.E 1000cc Car engine would have around 60hp whereas a bike engine can get towards 170hp. Life span of the engine is much lower, its uncommon to see galactic mileage on bikes…. The majority of sports bikes are 4 cylinder giving more power and revs. 2 cylinder tends to give more torque and more tractability. then a 3 cylinder tends to give benefits of both and single cylinders are light and can be used for off road bikes.

4 – You can turbo charge bike engines and it does give more power but with power outputs of 150bhp plus there really isn’t any need for it. Supercharging is also popular for the drag racers, but for a manufacturer the cost is prohibitive and in racing forced induction is not allowed. Also if a 600cc engine isn’t enough then 1000cc is available if that isn’t enough then 1300cc is used. And if that isn’t enough then perhaps a trip down the Army surplus stores is in order and strap yourself to the biggest rocket available.

I’m sure there are some points in there ill be corrected on, but thats my understanding of it all….

Turbos make for a lot of heat. Intercoolers are needed to to cool the intake charge. Packaging it all on a motorbike is rather tricky. Motorcycle manufacturers and riders are notoriously conservative

Turbos have been tried, but with little real sucess.
TJ is correct, but I’d like to add that I think it’s all down to feel. Turbo lag would be a problem, and a linear throttle response is more important than more power. When a bike like an R1 has 170bhp, it’s more about getting the power onto the road without looping the thing than having even more power.
If you’ve only ever driven a car, you really can’t even begin to imagine the performance available from even a bike like my little Monster 696 with a mere 80bhp.
The first time I opened the throttle on my newly de-restricted CB500, it took my breath away…….

Thats nonsense TD – Holeshot racing and BigCC racing have been sticking turbo’s on bikes for years with a turbo bike not being that much heavier than a stocker.

Honda and Kawasaki both had factory versions back in the day but neither really did very well, possibly because the wrong base bike was used. Had I not just accumulated some points I’d be considering sticking one on my Blackbird.

Its not cheap though and how much extra power do you really need on a bike that already does 170+mph

I’m pretty sure the point he was making was that the manufacturer wont do it but it is possible with a lot of extra plumbing and extra cost.

The real solution or simple lightweight motorcycle with lots of power is a modern 2 stroke…

Motorcyclists debate heavily over the 2-3-4 cylinder options all delivering different levels of torque, engine braking and smoothness. I don’t think it’s worth the development to design a mass market motorbike friendly turbo, when the likely hood it would be rejected.

Many 1000cc sports bikes can manage 0-60 in under 3 seconds without any modifications. There is no need.

Holeshot racing and BigCC racing have been sticking turbo’s on bikes for years

Maybe they have, but I’ve seen a bloke, at very close quarters, trying to get a turbod Hayabusa off the line on a drag strip. It either bogged down or wheelspan. It was an absolute bitch to contol by all accounts….
The bloke on the big, bog standard, BMW (K1200? The new big hypertourer, thingy…) was thrashing the pants off him! And I was’t that far behind him on a 955i Speed Triple….
🙂

Hold up – I’m disagreeing with TD about issues fitting it on a bike, which can be done without a big trade off in weight or space, not that I’m some sort of Turbo evangelist trying to convert you all.

For the record, I wanted a turbo on my blackbird, which is a big heavy beast good at going in straight lines and not much else. Should I require more power (?) then a turbo would prove a viable solution, rather than blueprinting, bigger cams and all other gubbins needed to hit the same power figures. Even then, is it really necessary on a bike with more power than an average family car?

As for a turbo’d R1 or similar, rather you than me.

If you want a demonstration of just how unecessary they are watch this http://video.google.co.uk/videoplay?docid=-6946569604612882573&ei=fpeeSemlIJLQjwKOrcCAAg&q=ghost+rider&hl=en
particularly the 280kmh+ power wheelies half way through!

Even then, is it really necessary on a bike with more power than an average family car?

Nope. That’s why they don’t make production ones!
🙂

you really can’t even begin to imagine the performance available from even a bike

I know. I once rode a crappy knackered old 185cc off-roader on a muddy field. I had not long passed my driving test, so I was all careful with it.. I let the clutch out to the biting point, gently gave it some throttle (I’d heard stories about people having wild crashes their first time on a bike) and once moved off… I thought ‘this is ok’ and let go of the clutch.. well I’d only been tickling it, and when I let go I went flying forwards thinking WOOOHEEEE!!! I thought that was fast as hell – I just can’t imagine a 1000cc thing.

Anyway:

5) What’s the difference in engine terms between say a super comfy touring BMW style 1000cc bike and a sports bike? Is the tourer much slower? Is the engine more like a car?

Molgrips –
I had a BMW R1100RS – sports tourer with 95ish bhp and a 3/4 fairing compared to 140ish from a 1000cc sports bike ( real dyno figures) The engine is tuned to produce more torque at lower revs – in top gear peak torque was about 80 mph and peak power about 125mph. It means far less gear changing if you are hammering itt. Whack the throttle open at 60 in top and its much quicker than a 95bhp sports bike – rev it out and its slower than a reved out sports bike.

Also much more comfortable riding position, much more protedtive fairing and very comfy pillion seat. No chain to lube and adjust.

The fairing was really good at 100mph in heavy rain you don’t get wet at all. You can open the visor at 130mph and have no draft. I did a 800mile day on it with no great discomfort.

Slower than a sports bike over 50 miles – much faster over 500 miles. I did a 300 mile A road run in under 5 hrs.