how does power band work???

[kxrider89]

how does power band work

[zephead400ex]

There are usually 2 of them, one blue, one red. They do need replaced every 3 months. Actually, I am just messing with ya, haha.

Powerband refers to the point of acceleration when the motor takes off and you start hauling ***. It is hard to describe, but can feel sweet.:D

Make sense? later

[big-guy]

An internal combustion engine will have a certain rpm range where it produces the most power with the most efficiency. The idea is to keep the engine operating in this range, via the use of different gear ratios. A four stroke will work better in the low to mid range, while a 2 stroke is happier up high, or "wound out".

[KASCHAK]

with different pipes.. and reeds..

a reed is iether open or closed..

when the pipe is putting back the perfect backpressure to pushe pistion down and the reed is opened.. it produces alot of power..

i didnt really describe it really good...

its when everthing is syncronised..

[tc300ex56]

if im not mistaken they are only on 2stroke

[TheFontMaster]

Originally posted by tc300ex56
if im not mistaken they are only on 2stroke

Npoe 4 strokes have them too. It's just that the 2 stroke powerbands are much more noticible.

[Quadzilla]

I hear that Walmart has powerbands on mark-down this week! :devil: :D :cool:

[cals400ex]

walmart might have rubber bands on mark down, but not power bands....

[IL400EX]

Originally posted by kxrider89
how does power band work

http://www.exriders.com/techarticles/twostroke.html

I"M puttin some reeds in the fo hunny this weekend I"ll let ya know how it runs when i get back in town...:macho :blah:

[UglyMotha™]

Originally posted by Rico
I"M puttin some reeds in the fo hunny this weekend I"ll let ya know how it runs when i get back in town...:macho :blah:



well it can't get any slower than it already is so what's it goin to hurt :devil:

[wilkin250r]

The "powerband" refers to the RPM range in which the engine makes most power, and acceleration is greatest.

Imagine trying to run your 400ex at 30rpm. It would be impossible. That would be 1 revolution every two seconds, and the fuel exploding inside your cylinder simply cannot burn that slowly. So extremely low rpms is simply not possible.

On the other side, imagine trying to run your engine at 15,000 rpms. The faster you move your piston and internal components of your engine, the more energy it takes. Eventually, it requires more energy just to keep your engine turning than the engine produces, and you have no usable output energy left over.

So does that mean at some "magic" low-rpm you suddenly get tons of power, and then it drops of again at some high rpm number? No, it's not just black and white, it's a gradual increase and decrease along the entire rpm range to give you a power curve.

[wilkin250r]

In a 2-stroke motor, the effects are HIGHLY noticeable, and it has to do with the exhaust pipe. As the tech article posted above explains, the engine creates a series of pressure waves inside the pipe, but before I get into that, let's look at how power is created.

What are the two main factors to creating power? The amount of fuel/air you can burn (related to displacement) and compression of the engine. In a 2-stroke, both the intake and exhaust ports are open at the same time. Imagine it slowly, as the piston begins to move upwards, it will push some of the fresh fuel/air out of the exhaust port until the port is completely closed up. Not only do you lose some fuel/air, and thus lose power, but you also don't start to build compression until the exhaust port is completely covered (the intake port is already closed). So you have less fuel/air to burn, and a low compression, resulting in a low power output.

Now, enter the exhaust pipe into the picture. The exhaust coming out of the cylinder (before the fresh fuel/air enters) creates a pressure wave inside the pipe. It gets reflected back in two sections, a negative pressure (vacuum) wave and a positive pressure wave. The negative pressure wave will help pull exhaust out and new fresh fuel/air in, and the positive pressure wave will help keep the fresh fuel/air from escaping out the exhaust port.

So what does the whole picture look like together? At low RPMs, the piston is moving slower. The exhaust port isn't open yet when the negative pressure wave hits, so it's wasted. The positive pressure wave hits as the exhaust is opening, so the exhaust has to really fight to get out, further reducing power. And then we get all the problems that were discussed earlier with the fresh fuel/air escaping out the exhaust port and low compression.

Now when the engine hits a certain RPM range, magic happens. The negative pressure wave hits exactly when the exhaust port is open, so it sucks out all the exhaust, and helps pull in a fresh fuel/air mixture. Now, as the piston is moving upwards and the fresh fuel/air is getting pushed out the exhaust port, the positive pressure wave hits to stuff it all back inside the cylinder, and you actually start building compression even before the exhaust port is fully closed.

So with MORE fuel/air, and higher compression, you get a dramatic increase in power. So if you look at the entire RPM range, at low rpms you have very little power, then when you hit a certain RPM (based on the design of the pipe) you get a huge power increase. At higher RPMs, the power begins to fall off again. So you have lots of power within a certain rpm range, which is referred to as the "powerband".

[Toadz400]

Wilkin..you never cease to amaze me with your explainations!

I think he hit it right on.

All I know is that Banshee's and YFZ450's have sweet ones:p .

Oh and for Jumbo747...maybe if you read this through, I HAVEN'T RIDDEN A 450R YET. Just to remind you incase you decide to post something again;) .

[04'400ex'er]

W O W ! ! !


I can't believe some of yall are tellin all these lies. You can only buy these powerbands at the licnesed dealers. They are made from a special rubber compound that dosen't wear under the extreme power of todays machines like the 450's. The green type are for top end, and the red are for bottom. Wilkin, you have let us down.



Haaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:eek2: :eek2: :eek2: :eek2: :eek2: :eek2: :eek2: :eek2: :eek2: :eek2:

[Sprks450r04]

quote:
--------------------------------------------------------------------------------
Originally posted by tc300ex56
if im not mistaken they are only on 2stroke
--------------------------------------------------------------------------------


actually every internal combustion engines have power band but two strokes have the most noticable ones

[kxrider89]

quote:
--------------------------------------------------------------------------------
Originally posted by tc300ex56
if im not mistaken they are only on 2stroke
-------------------------------------------------------------------------
in every internal combustion engin there is power band. but in 4 strokes it is not felt but in two strokes you can really fell it.

[airheadedduner]

Originally posted by wilkin250r


Now when the engine hits a certain RPM range, magic happens. The negative pressure wave hits exactly when the exhaust port is open, so it sucks out all the exhaust, and helps pull in a fresh fuel/air mixture. Now, as the piston is moving upwards and the fresh fuel/air is getting pushed out the exhaust port, the positive pressure wave hits to stuff it all back inside the cylinder, and you actually start building compression even before the exhaust port is fully closed.

Your neglecting the very strong importence of the transfers in this process:p

Not only does the presure wave have to coincide with the exhaust port duration but it also matches with the transfer port duration. As the fuel/air charge is also being sucked through the exhaust by the presure wave the downward force of the piston presureizes the crankcase and forces a fuel/air charge up through the transfer ports which is directed across the top of the piston and pointed slightly back twards the intake. It kinda forms a fuel air "wedge" that loops through the cyinder and shoves out any residual inert gas that the pressure wave was unable to remove on its own. There are a half dozen things that have serious effect on the powerband on a two stroke...........and they all have to work together:huh

If you want to see what a power band looks like look at a dyno chart;)

http://www.imagestation.com/picture/sraid32/p1fccf8ecddfcf3fe9e4caed436126d70/fd41625b.jpg

[chucked]

if im not mistaken, isnt there a mechanically driven valve in some 2 strokes that actually opens up the exhaust valve more at certain rpms?

[Flo Bee]

Originally posted by chucked
if im not mistaken, isnt there a mechanically driven valve in some 2 strokes that actually opens up the exhaust valve more at certain rpms?

"Power valve?"

[LazeR]

There is a powerband in everythign with an engine. Even cars and trucks! Just not near as noticeable as say a 2 stroke engine!

[Flo Bee]

Originally posted by LazeR
There is a powerband in everythign with an engine. Even cars and trucks! Just not near as noticeable as say a 2 stroke engine!

Ford's modular engines kick in just like a two stroke when using a set of aftermarket billet cams. More or less, it's the part of your hp/tq curve in which the vehicle pulls hard.

Lotsa good info in this thread. Definitely a good read for beginners.

[04'400ex'er]

Originally posted by chucked
if im not mistaken, isnt there a mechanically driven valve in some 2 strokes that actually opens up the exhaust valve more at certain rpms? It's the powervalve
It controls the flow of the exhaust at lower and higher RPM's Mine got clogged on my KX and fu$%ed it all up.

[Woodsrider]

Originally posted by 04'400ex'er
W O W ! ! !
I can't believe some of yall are tellin all these lies. You can only buy these powerbands at the licnesed dealers. They are made from a special rubber compound that dosen't wear under the extreme power of todays machines like the 450's. The green type are for top end, and the red are for bottom. Wilkin, you have let us down.




Only Polaris offeres a replaceable power band, but it clearly states to not get them wet or they will slip:devil:

[airheadedduner]

Originally posted by 04'400ex'er
It's the powervalve
It controls the flow of the exhaust at lower and higher RPM's Mine got clogged on my KX and fu$%ed it all up.

What the PV does is change the port duration(time the port is open). At low RPM's too much intake charge is lost out of the exhaust port that the exhaust can't scavenge back into the cylinder on its return wave. By shortening the duration you can keep more charge into the cylinder.