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

[classic zed]

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

reminds me of the time I was sent to the stores (2nd day of first job) to get a box of sparks for the grinder, the storeman asked "do you want blue or yellow sparks" I didnt know so I went back to ask, everyone was pissing themselves laughing, Bastards.:doh:

[Motu]

You guys are full of shit,stop pulling his leg - it's an old joke mate,and they all sucked you in!

Any good mechanic KNOWS that when you install new powerbands it is CRITICAL to lube them with elbow grease or they will not slip properley into place. And if THAT happens things get pinched badly. That reduces the power due to the non-egagement of the power band and the bike ends up with a super high exhaust pitch that sounds like Alvin the Chipmunk on steriods and caffine all at once but with no power at all.....

I've planted some in my garden this year,they are coming on nicely and shoud be ready by early feburary I reckon.I'll try them on my bike first,then let you know....I might sell some here,they'll be much cheaper than the dealers or even Mitre 10.

[SlowHand]

Hi

Between 1976 & 1982 all of my bikes were single cylinder
4 strokes. In 1982 I bought a CB750, my first experience of a
4 cylinder bike. I bought this bike due to it being on sale at
only $1000 more than the cost of updating my XL500 to the
latest model. The 750 initially felt quite sluggish in comparison
to the XL500 due to the fact I was only revving it to accelerate
by the same amount as my old XL. It took me about 6 months
to discover that it had a different powerband to my old XL as
I was never told by the dealer the different charactaristics
of the DOHC 4cyl in comparison to my XL500.

Good song that - who's it by again?

[Ivan]

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!

Hey Id argue bout that I have an RGV slower and less powerbandy to the RG and dragged of a V8 Falcon at the lights on my RGV and he was going flat tacker I held rev at 6G an when those lights changed green just gunned it throttle wide open I aint lost a light race yet

[roger_doger]

I may be missing the mark here but I think there may be a bit of confusion here stemming from what is correctly known as a powervalve. A powervalve is a sort of sliding plate that is attatched in front of the exhaust port of two stroke bikes (motocross and some road). The reason is that because high performance two strokes have large expansion chambers to produce high power, they would otherwise suffer greatly in low to mid rpm power because of the lack of exhaust back pressure. Different setups are operated either by cable or electronically. The "valve" is down at low rpm to create more backpressure (and power), and then opens at higher rpm so the bike can produce maximum horsepower.

The effect of all this is that in real riding conditions, it creates a sudden surge in power when the valve opens, which is a trademark of any high performance two stroke.

The confusing bit is that a powervalve is often called a powerband. But that word is also used when describing the power delivery of any motor.

But to be clear, powervalves are only present in the form described on two strokes. There is additional confusion to this saga however as Yamaha, and more recently Suzuki, have used the same principle in their four stroke sports bikes in the form of valve located in the middle of the exhaust system. This setup is used for the same purpose as a powervalve in two strokes

Just my 2c worth

[TwoSeven]

yes, a 4-stroke powervalve as in the zorst changes attenuation length and for different rev ranges. Suzuki's is rather interesting as they also use it to allow for a short fat megaphone.

[Skyryder]

And here's me thinking a power band is a Rock band pumping iron.

Rode a mates 350 Kawasaki a few years back. Just down right dangerouse. Those mothers had a lethal power band. The powere to weight ratio was from another planet. If memory serves me right more riders came to greif on the 350 Kawa than any other bike.

Skyryder

[TwoSeven]

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.

This is a characteristic these days of fuel injected bikes with all that electrikery. The higher the value of the number is what gives it the ability to wheelie (its rate of acceleration) - the change in the number simply gives the bike a characterstic.

Torque curves on dyno charts are odd to read. Its actually telling you the acceleration characteristic of the bike at a given rpm and power (so you read it as a point - not a range of values). If its the same number all throughout the power range, then the curve will be flat and the bikes acceleration will be roughly predictable.

Thing is, if its a constant power, and the power curve is linear then its going to progressivley accelerate and be boring. What you need is a 92, cbr900, the first R1s etc, or even kevin schwantz's old bike (suzi). These machines had linear power curves, but the torque curve was a random number based on the day of the week :)

You'll hear magazine writers say that the bike was 'flat' and lacked passion. Often you'll see that the torque/power curve is flat an linear as well.

Then there are carb based bikes that have different rates of torque, the journos will say things like - savage delivery, unpredictable (I think fun) - you'll see torque curves at really silly places.

[marty]

look here>>> http://reviews.ebay.com/How-a-2-stroke-RC-exhaust-works_W0QQugidZ10000000000014651

and power bands only work properly once they are tensioned with a long weight, as opposed to a short weight, which is something as an apprentice, you would be unlikely to be able to find a part number for.

[pritch]

Probably to start off another argument,


I get the impression that if you really wan to start an argument you should place the controversial statement near the beginning of your post where those with short attention spans might see it :devil2:

[Beemer]

Oh for heaven's sake, if anyone on an RG150 thinks they can drag an R1 off in a race (not a car of any make or model, but a BIKE), I'd like a bet on the outcome! I had one for four years and while I admit it was a lot of fun, there was NO WAY IN HELL I could have got the jump on a more powerful bike. If you guys reckon you can, I reckon you're full of shit!

[GNR]

wow, lots of replys,
thanks for that guy/gals, i was hopein for somthing more exciteing, but i see how it work,

another important fact to add to the brain

[crash harry]

The confusing bit is that a powervalve is often called a powerband.
Just my 2c worth

Really??? Only by someone who's getting the words confused together I think...

EDIT: Just realised that that sounds really sarky... wasn't really meant that way...

[Mattyc]

on a 2 stroke, the powervalve (on my bike anyway) increases the exhaust timing by opening a flap at mid rpm that actually makes the exhaust port higher in the barrell, this gives the bike a good hit

the pipe on the other hand has a lot to do with it too, the pipe works sort of like a supercharger and the exhaust waves reflect back into the engine forcing unburnt fuel into it, with the pipe its all about length , I race model powerboats with 10cc methanol engines, that also run a percentage of nitromethane, boats are around 12lbs and do about 80kmh or more when tuned right, we run pipes with expansion chambers , the shorter the pipe generally the longer it will take to get on pipe (powerband, rubberband, whatever) but when it does it will hit harder, the longer the pipe it will generally get on pipe quicker and have a more gradual powerband with less hit... the rule of thumb is for mixture - long pipe leaner mixture, short pipe, richer mixture (fuel air, not fuel oil)

word