can some body tell me how the power band on mxer's work? and do trials bikes have a smooter version of these to make them grip better?

To put it really basicly a powerband only happens on 2-stokes when they reach a certain rpm where the engine works really well.

and yeah, a trials bike do have really smooth power bands the last thing you want on a trials bike is for it to suddenly blast off when it reaches a certain Rpm

There are different powerbands for the mx'ers.

Mx'ers rev quick, even the 4-strokes. Spin like crazy everywhere.

My sherco 290 maybe has 16hp at 6000 rpm. Smooth slow power

My 2 stroke 250 bursts at low rpms( 4000) then revs smoothly till about 9000. 45hp

My 4 stroke 250 revs like crazy to make power. 8000-13,000 32hp

My 4stroke 500 is smooth power from low down and the more you want the more you rev, till about 9000. 48hp

I think your getting mixed up with a power valve, these are found on 2 stroke mx'ers. When the engine gets to a certain rpm a valve on the outlet port opens to allow the exhaust gases to leave the engine easier and so in turn allows the engine to build more rev's very quickly and so makes the bike go quicker,

It feels a bit like a turbo on a car. Where as, every bike has a power band as this is just where the power is in relation to engine rev's. ie some bikes have a lot of low end power for example a trials bike, where as a 125 mx'er has the power range all at the top of the rev range. Hope that explains it a bit better.

the reason for trials bikes not having powerbands cause they dont really have an expansion chamber. on mxers you do and depending on the shape of the pipe is where your powerband differs. like on my 50cc road bike the power band kicks in at 9500 and finishes at 14000. where as before it started at 6000 and fineshed at 11000 with the origional de restricted pipe on it because the shape differs

Hummm

Well ALL 2-strokes have power bands its just that some are alot more noticeable than others

dont be cocky. i bet everyone else knew what i ment you cant really call it a power band it is more like a power curve because all the power does not come in a big surge.

Edited May 6, 200521 yr by beta boy

beta boy is right about the shape of the expansion chamber and it's effect on a power curve.

The harmonics of an exhaust pulse leaving the cylinder are amplified in the expansion chamber to bounce back and forth within it. A shock wave leaving the cyliner helps draw fuel mix through the engine, while a returning shock wave helps seal it ( in the absence of valves) and prevent the unburnt mixture going straight out the exhaust.

the shape of the pipe affects the frequency and amplitude of these shock waves, which in turn affect the way in which fuel is burnt at certain points in the rev range.

Power valves work to alter port height at certain RPM so that tuners can 'have their cake and eat it' so to speak. Certain exhaust port height dimensions work better at high or low revs ( Or in between). A variable exhaust port height allows greater efficiency at a wider rev range.

Sorry if this is basic and doesn't make much sense, but I'm hung over and it's been a long day......

I used to have an RD350LC, the power band on that was fantastic and there was no power valves in the exhaust. They came in the YPVS version.

Edited May 12, 200521 yr by boofont

Boof, funny thing that progress , i also had an elsie 350 , then got a power valve , lavished a fortune on her , nikon pipes, WP rear shock , WP front springs , fancy steering damper , the works and it still wasnt a patch on the old elsie !

That one your boofont? Very nice example! I've got a '73 RD350 in my garage in several boxes, just dying to see the tarmac again...shame it will never look that good though.

Not mine I'm sorry to say although its the same as the one I did own, I sold it to fund the Scorpa. I'll get another one one day, they're a classic for sure!