How does powerband work?

[GNR]

As above ^^^^ anyone got any links etc? Cheers

[Ixion]

Mate you are SO going to get your tit pulled with a question like that! C'mon Mr Motu, I'm waiting with bated breath for you to explain about powerbands.

[SPORK]

As above ^^^^ anyone got any links etc? Cheers

A powerband isn't a THING, really. It's more a representation of how the bike delivers power. A steep powerband on a dyno chart would mean that it builds up power quickly etc.

I'm pretty sure I'm talking out my arse though. Ixion's on the case, so I'll be proven wrong.

Edit: Mebbe not...

[pyrocam]

its got something to do with the piston hitting the magical fairy dust on the top of the barrell.

[Coyote]

The powerband is what kicks you off a 2 stroke and breaks your legs

[Sketchy_Racer]

power band is cause by when all the ports in a two atroke are flowing proprerly , thats why you can port a two stoke and get a bigger 'powerband'
as omgwtfbbq said its not realy a thing its just the way the engine makes power

[Ivan]

Yeah what they said like on a RS125 you have a real Narrow power band and thats what you have to ride in for the bike to perform power ya know but at the same its nasty look at them 500GP machines they were wicked

[Ixion]

OK. Serious answer to serious question

We all know what horsepower is - it's what makes the bike go fast.

Horsepower is , by definition, torque multiplied by revs. Torque is how hard the crankshat is trying to turn on each revolution. The amount of "push" the pistons are applying. Multiply the amount of push on each stroke by the number of revs per minute and you have a horsepower figure.

Some engine have what is called a "flat torque curve" It's never actually flat, but it can be flatter than others, less of a curve. This means that the amount of torque is about the same at any given revs. So the horsepower will be directly proportional to the revs. (Bearing in mind that a truly flat curve is never found).

In terms of riding this means that opening the throttle will make you go faster , but it will be a steady progression - no point at which it suddenly "takes off". Most family cars are like this.

Other engines (eg racing ones) have a certain point, usually quite suddenly, in the rev scale where all of a sudden the engine starts producing a LOT more torque on each rev. So the more revs, you get a double increase in horsepower - more revs AND more torque on each rev.

This effect can start quite suddenly , at a certain rev figure. If it's very pronounced it can make a bike hard to ride. Opening the throttle will increase the revs, bike goes faster but nothing dramatic, maybe even boring. Suddenly, without any warning, the engine gets to the point where torque increases a lot. So horsepower increases a LOT - and SUDDENLY. From a riders point of view, all of a sudden the bike "takes off". Maybe suddenly enough for the front wheel to come up, or the back wheel to break traction. Which can be rather nasty for an inexperienced rider if it happens on a corner in in the wet.

The point on the rev scale where this happens is called the "powerband". And we speak of being "in the powerband" or "out of the powerband".

The effect is caused by engine design - valve sizes, timing, lift in four strokes, porting in two strokes, exhaust and carbs in both, lots of other things.

Tuners can play around with the engine, modify the powerband characteristics, make it happen earlier or later, fierce or less fierce etc. Be warned that such tweaking is a black art and amateur efforts can (and usually do) produce less horsepower rather than more.

EDIT: Most bike engines fit in between the extremes - between racing engines and Mummy cars. And as someone else noted, at the end of the day there's no substitute for cubes

[Beemer]

What Ixion said, but if you have an RG150, don't get all excited and expect to drag off an R1 at the lights - their powerband is fun, but NOT QUITE as powerful as this explanation!

[Warren]

On a two stroke the powerband is more dictated by the exaust cone that reflects the noise and the negitive pressure sucks the exaust out, increasing power (or something like that). More heavily tuned bikes have a narrower powerband and sacrafice all-round even power for a powerful powerband but little power elsewhere.

[pyrocam]

What Ixion said, but if you have an RG150, don't get all excited and expect to drag off an R1 at the lights - their powerband is fun, but NOT QUITE as powerful as this explanation!

dunno what your talking about. my rgv150 could take anything. just took a sec to get into powerband then I was GONE.

[SPORK]

Some engine have what is called a "flat torque curve" It's never actually flat, but it can be flatter than others, less of a curve. This means that the amount of torque is about the same at any given revs. So the horsepower will be directly proportional to the revs. (Bearing in mind that a truly flat curve is never found).

If any of you want an example of this, look at a dyno for an 05 Triumph Speed Triple. It has the flattest motherbeast of a torque curve ever. And they say it is the best wheelie bike evar made.

[TwoSeven]

To me the 'powerband' is simply the part on a dyno chart that reflects the steepest and highest part of the power curve (the bell shaped part of the power curve that contains peak power).

From the engine perspective its tuned by adjustment of intake, cylinder and attenuation (exhaust) tuning. From the bike perspective, you factor in gear and final drive ratios. The principle is similar for 2-smokes and 4-smokes, but the method of actually doing it is slightly different [two smokers insert complaint here].

To use an example, my old cbr250 ran a rev range of 0-20,000 rpm. It developed peak power at 14500rpm with the slope (of the bell curve) starting at 12500rpm and ending at 16000 rpm. This gave a powerband of 3500rpm (16-12.5) of which 1000rpm (it double peaked) was at peak power (+/- 1bhp).

When I got it, peak torque occured at 11,000 rpm with the curve starting at 10,000rpm and ending at 12,500rpm. The term torque band is not as widely used but it should be as its just as important. Anyhow, the two nifty has a pretty good torque band, but its in a sucky position.

Primarily you can move the torque and power bands up and down the rev range by adjustment of the attenuator and megaphones (changing the exahust system), you can then be more subtle by modding other bits.

The gear ratios dropped of 3-4k rpm (the 250 never was precise), which meant that if I changed up gears at just past peak power, it would drop down to just on the start of the power band. Likewise, downshifts had to be managed in a similar way. The problem with peak torque being down so low, meant that the bike was never as agressive as I wanted it to be. I'm in the process of fixing this on my 600 with working out a new exhaust design which I think might work better.

Probably to start off another argument, in really basic terms, torque is telling you how a bike will accelerate, the torque curve is telling you about the characteristics of its acceleration - but its not its actual acceleration. The power curve is telling you how quickly the bike will be capable of acceleration (how responsive it will be to throttle manipulation) and is known as its driving force - its ability to drive the bike forward. The two are related to each other. A bike with high torque and now power will be sitting still, so will a bike with high power and no torque (it would probably be in neutral).

In my example of the 250, the torque curve was flat at peak power - hence it felt sucky, but just under the power curve when peak torque occured, the bike could life the front wheel and felt like it went like the clappers. Hence I think the bike would have been more exiting if the torque and power curve is matched.

When looking at the powerband from a gearing perspective - which is important on a 125 and 250cc bike. Its important that the power band is wide enough so that the gear ratio will not cause the bike to lose its drive when a gear is changed by dropping too far below peak power (out of the bell curve). Ask any 125 rider what happens when the get the gears wrong for a corner. For small capacity 2-smokes, this is where the art of engine tuning is I think.

I know there is a technical math based description, but the above seems to work for me.

[texmo]

When i started to work at scooter world they sent me down the road to get some power bands........ FUCKERS

[classic zed]

Expansion chambers can make a huge difference to how a 2 stroke performs.
Back in the 70's (now I feel old) we had about 3 different sets of pipes for the Mk6 RG500 GP bike, we used different pipes for different curcuits depending on whether we wanted a lower rpm short band, for those twisty curcuits (eg Cadwell Park, UK) up to a higher rpm more gradual band for the faster circuits (eg Paul Ricard, France).

Check it out
http://www.motorcycle.com/mo/mcnuts/em-pipes.html