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Re: [ST] Higher RPM for racing?

On Wednesday 23 August 2006 08:25, Andrew Tait wrote:
> 600cc is the amount of fuel/air mix burnt every two rotational cycles,
> so at 6,000rpm we're getting 3,000 "bangs" worth of energy every minute,
> and at 12,000rpm we're getting 6,000 "bangs" worth.  Twice as much bang
> power.

It's a bit more complicated than that - the engine won't be 'on the cam' at 
low rpm and at very high rpm will be struggling to suck in enough fuel/air 
mixture. Both mean that the cylinder doesn't completely fill with fuel/air 
mixture, so torque falls off at both very low and very high rpm.

At the peak torque RPM each combustion cycle is working at its most efficient. 
You need a lot of clever cam lobe, intake and exhaust design to flatten out 
the torque curve (if a wide smooth powerband is your aim) or move that peak 
torque value as high up the rpm range as possible (if peak power is your 

In the latter case the torque will fall off before peak power rpm is reached, 
but because hp = torque x rpm, more revs means more power even though torque 
is already falling off. Eventually of course the loss in torque can't be 
overcome by more revs and the power peaks then tails off.

Having owned a CBR600 a few years ago, there is a fun factor in having a motor 
with a big high-rpm power kick, but having to change down 2 or 3 gears to 
overtake rapidly is a pain. I reckon the ST achieves a great compromise 
between bottom end and top end for street riding.


'04 ST955i

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