Cylinders, Torque, and RPM query?

[Rasher]

Marki hit the nail on the head, you need to look at more than just a peak torque / rpm figure, the spreadis also a factor, perhaps a better way to "judge" an engine is by the area under the graph (be it power or torque)

The GS has a good 20BHP gain on the Corser, at the expense of a few rpm, considering it is an aircooled twin against a multi-cylinder liquid cooled engine (I assume the Corsa is 3 or 4 cylinders)

My ZZR1400 had about 170BHP at the wheels, double that of most four cylinder cars of the same capacity, but revved to 9,000rpm to achieve it, in a bike it was a torque monster, yet it would feel a lot flatter in a car, you could help by gearing it down from 200mph top end to 120 and it would make for a bloody fast hatchback engine - but still feel very buzzy and completely opposite to how it feels in the bike.

Twins tend to have good low-midrange torque compared to fours which may produce more torque on paper, but it is at higher revs.

Sometimes science and figures does not tell the full story, the best thing you can do is try to get a go on a single, twin and four cylinder bike and is possible with similar power outputs.

Try and ride something like a CBR600 then hop on a Ducati 849, or swap your GS for a Tiger 1050 for a couple of hours and then try a VFR800 - you will feel the difference that the numbers do not show.

 

[ianp5uk]

I watched the early Honda NR racers at Silverstone, Assen and Spa, ridden by Mick Grant, Fast Freddie Spencer etal. Total junk.

Maybe but obviously everyone was shitting themselves they could sort it quickly or they wouldn't have been so quick to ban it.

 

[ianp5uk]

Twins Vs Fours?
Twins definitely seem better at producing torque at lower rpm not sure that is important as it's rev range that counts really. But there is a definite different feeling in the way the power is delivered and I guess the impact on the tyre's grip. In terms of ultimate power it's about rpm and fours can rev higher because of the aforementioned piston speed being lower.

 

[Giles]

This has been (is) a very interesting thread, I've bugger all to contribute, 'cos I have no engineering knowledge, but a big thanks to the engineers (Mark ) for their input .....

 

[snerkler]

I get what your saying and in part your right but your not comparing like for like. A 1200 Corsa engine isnt tuned the same as a 1200 boxer. A Corsa doesn't rev to 8000-8500 rpm for a start and it only has 80bhp. Could a boxer out torque a Corsa, very definitely yes. So why doesn't it? Because the masses are fooled into thinking that the BHP figure is the be all and end all and demand more. You see it all the time in this forum. People clambering over another 5 BHP and spending vast sums of money to do it. For a manufacturer to get the extra horse power you have to either rev it harder or increase the CC and that's a trade off at the expense of torque. If you detuned a 1200 boxer to 80BHP the torque would be much greater than it is just now and a lot lower down. Its also a fact that a bike can easily trade torque for BHP because of its much lighter weight and bike riders are used to short service intervals where car drivers demand at least 1200 miles.
The part you are right about though it that packaging is far more important so long as the choice can do the job. A car driver wouldn't put up with the levels of vibration that a biker will so a twin is out. A 1200 GS-A wouldn't be the same bike with a 4 in it and it would probably be even heavier and taller than they are already. You could do a flat 4 but then you would smash your shins all the time or have a longer bike. A single cylinder crosser would just be completely unmanageable with a 4 in it due to weight and size. Whatever engine a manufacturer chooses above all it has to be able to do the job the vehicle is designed to do and fit in with what people want so they buy it.
The likes of Ducati were lucky in years gone by because WSB heavily favoured them. Not because a twin was better than a 4 but because the other manufacturers were handicapped by the rules meaning the twins were competitive. Because of patents on the Desmo valve system nobody else could make a twin that could really compete. Yes Desmo valves are that good but only in the short term as its complicated and requires a lot of maintenance. The rules were changed and the twins were on a more even par so the fours started wining again. Many a racing fan bought the big twins because they were winning races but in reality the GSXR's and the like were far better road bikes.

Thanks again for your input.
Obviously there are many factors invloved in engine performance, figures etc etc, and I appreciate that it is not as straight forward as just looking at cylinder size and storke length.
As I said before, the reason for my continual questioning is that few of the answers made sense for my initial question. And as it happens I've found that my question was wrong in the first place, Twins and singles don't necessarily produce more, or lower torque it's just that they're tuned that way.
In response to Rasher, I know that different cylinders produce their power/torque in a different way, and not only does this make sense theoretically, I've also experienced it first hand as have ridden paralell twins, boxer twins, triples and straight fours. Of all the engines the DOHC is my favourite in terms of 'characteristics'.
I have also been fortunate enough to drive cars with a straight 4, straight 6, V8 and V12 and in terms of characteristics the V8 is my favourite.

I know that some of my examples have been extreme comparing a boxer twin to a japanese 4, to a car 4. They were just purely to show that, for the same engine size, a straight 4 can produce the same torque as a twin, and a straight 4 can produce lower torque than a twin, and that these factors are not necessarily 'traits' of an engine, more to do with how the engine is tuned. So it does appear as though I've uncovered a few myths.
This of course is not referring to how that power/torque is actually delivered, which does seem to be more a trait of each particular engine. This may be what people actually mean when they say twins produce good low down torque, and could just be a bad and confusing terminology

 

[snerkler]

For a manufacturer to get the extra horse power you have to either rev it harder or increase the CC and that's a trade off at the expense of torque. If you detuned a 1200 boxer to 80BHP the torque would be much greater than it is just now and a lot lower down. Its also a fact that a bike can easily trade torque for BHP because of its much lighter weight and bike riders are used to short service intervals where car drivers demand at least 1200 miles.
.

I understand what you're saying here, and I for one prefer torque, especially low down, to HP. Within reason of course. BMW have done a good job with their new boxer engine, increasing both torque and HP. If I'm being picky I would have rather them not increase the rev range and hence raising HP, and instead given it a bit more torque. That being said, I love the DOHC boxer

 

[Rasher]

Maybe but obviously everyone was shitting themselves they could sort it quickly or they wouldn't have been so quick to ban it.

The NR500 was never truly competitive and eventually Honda withdrew it when they realised a f**** great heavy four stroke was never gonna compete with the much lighter two-strokes, que NS / NSR500's and a string of world titles.

The NR technology was then put to use for endurance racing, as back then this was a prototype class of four stroke 750's and provided a more level playing field.

Seeing as the NR had 32 valves, 8 conrods, 8 exhausts, 8 spark plugs it is easy to understand the whingeing of those without such technology, but maybe if they had been allowed to continue we would have amazing oval pistoned road bikes available today.

Ignore the NR750 road bike, this was so dumbed down, £38k for a bike that was far heavier and less powerfull than the Fireblade (About £6k at the time) and not a patch on the awesome RC30 (About £10k)

Rumours where that Honda had considered making it fast and light, possibly fitting an Elf type front end before someone pointed out they could just bling it up a bit and save on making it powerful and light cos as sooon as you stick a £40k price tag on a motorcycle and make it a limited edition all those people with more money than they could ever spend in a lifetime will come knocking on your door - and as they will never get ridden it don't matter how well they perform, as long as they look good on the mantlepiece - I still quite fancy one though.

 

[Deleted account 190920001]

The NR500 was never truly competitive and eventually Honda withdrew it when they realised a f**** great heavy four stroke was never gonna compete with the much lighter two-strokes, que NS / NSR500's and a string of world titles.

The NR technology was then put to use for endurance racing, as back then this was a prototype class of four stroke 750's and provided a more level playing field.

Seeing as the NR had 32 valves, 8 conrods, 8 exhausts, 8 spark plugs it is easy to understand the whingeing of those without such technology, but maybe if they had been allowed to continue we would have amazing oval pistoned road bikes available today.

Ignore the NR750 road bike, this was so dumbed down, £38k for a bike that was far heavier and less powerfull than the Fireblade (About £6k at the time) and not a patch on the awesome RC30 (About £10k)

Rumours where that Honda had considered making it fast and light, possibly fitting an Elf type front end before someone pointed out they could just bling it up a bit and save on making it powerful and light cos as sooon as you stick a £40k price tag on a motorcycle and make it a limited edition all those people with more money than they could ever spend in a lifetime will come knocking on your door - and as they will never get ridden it don't matter how well they perform, as long as they look good on the mantlepiece - I still quite fancy one though.

I couldn't agree more about the rules and all that. To me at the top level of racing there should be very few rules and let innovation take over. If its a crap idea it will probably fail. If it works then it will feed back into the production world. Hope your listening Mr Ecclestone because your F1 is just plain dull due to your your meddling! So drop the rules and lets see who is the first to make a W8 ceramic engine with no cooling system and 95% efficiency.

 

[Engineer]

It is myth that twins produce more low down grunt that multi-cylinder bikes. The new bmw 1600 produce masses of low down grunt. The main advantage of fewer cylinders is their relative simplicity.

 

[snerkler]

It is myth that twins produce more low down grunt that multi-cylinder bikes. The new bmw 1600 produce masses of low down grunt. The main advantage of fewer cylinders is their relative simplicity.

That's what I've realised after all this research
I think it's fair to say that the way the 'grunt'/torque is delievered is different though, and so far the delivery of the DOHC boxer is my favoutire to date, followed by the 4 of the K6 Gixxer thou, and then the 1050 triple of the Tiger.
I would love to try a Harley just to experience one, although they're really not my bag.