whats with this whole power band thing?

[Clint Allison]

kf tree,
Have you ever ridden a 2stroke dirt bike? Do you remember when you rode one for the first time? You know when you whacked the throttle at low rpm's and thought it didn't have much power, in an instant the front tire looses all intrest with the dirt, you are on your back and the bike is sliding across the ground. That's a powerband.
Clint

 

[kf_tree]

kf tree,
Have you ever ridden a 2stroke dirt bike? Do you remember when you rode one for the first time? You know when you whacked the throttle at low rpm's and thought it didn't have much power, in an instant the front tire looses all intrest with the dirt, you are on your back and the bike is sliding across the ground. That's a powerband.
Clint

clint

problem is i've never ridden a dirt bike.........but i did own a 95 zx7 with a 95zx9 moter stuffed into it.

 

[Clint Allison]

Great,
You know how that motor was very soft/fluffy from idle to around 6000rpms or so then explodes into power around 9000 rpms? That's it.
Clint

 

[ol'homey]

The saw will cut the fastest at the RPM where HP peaks. So if for example you have a stock Stihl saw you wish to tweak, you simply call the Stihl 800 tech line and have the tech find the service manual for your saw. In the service manual he will find the rated HP and most importantly the RPM that rating was achieved at. Do not confuse the max. HP rpm (might be say 9500), which is what we want, with the max. operating RPM (might be 13,500) which easy to find in all the literature. The max. operating RPM is used for carb tuning and to keep the saw from blowing up. You don't cut wood at max. operating RPM because the engine doesn't make any power there. As soon as you put it in a cut the RPM will drop. The ideal load would cause the engine RPM to drop to the max. HP RPM. Go buy a small tach (Stihl makes a good one) and attach it to your saw. You can then play with various combinations of sprocket teeth, bar length, chain type (.404,3/8,.325 full comp, full skip, RS, RM etc.), and raker depth to get the saw to turn close to the max. HP RPM when you are cutting the largest diameter hardest wood you normally encounter (which is where you need max. HP).

 

[JohnL]

It's been my understanding, that two-strokes don't suffer from "over-reving" like a four-stroke would.

In other words, a four-stroke can actually rev too high, and thus, the power drops off, and/or engine damage can also result.

TRue, in 4 strokes you've got to carry the valvetrain, when the revs get high enough the valves start to float on top of the cam, not closing all the way, getting out of time with the crank.

But the other aspect that both 2 and 4 strokes are subjected to is the flow dynamics of the incoming a/f charge and outflow of exhaust, which controls at what rpm the best power is made, and how wide the range in rpm . In either case you are limited to a range in rpm where that fixed port or valve timing works for the engines, go beyond it, they stop breathing as well, power falls off.

 

[chainsawworld]

powerband is when the engine is running at its peak, making power. it is harder to detect with the smaller chainsaws as it is it with the motorcycles and snowmoblies. you can actually feel the bikes and sleds "take off" when the powerband is reached. fuel delivery and ignition are creating the most power. most times this occurs just under full throttle. just under full throttle meaning being driven, not in neutral, and cutting, not screaming out of the wood with the carb. shutter or slide wide open. when cutting the operator has to listen and feel for the powerband to keep correct pressure in the cut much the same way a rider has to select the correct gear in the gear box.
marty

 

[J_Ashley]

Ride a 2-stroke Sea-Doo. Cruise at about 30mph, and then punch the gas. When the sluggish acceleration then wants to rip your arms from the handle bars, you'll have jsut experienced, first hand, what a powerband is.

Justin

 

[jp hallman]

Cheers Al. I've given up on the pills and switched to Crown Royal and Coke.

Why ruin good whiskey? Neat, in a tall glass!

 

[Simonizer]

TRue, in 4 strokes you've got to carry the valvetrain, when the revs get high enough the valves start to float on top of the cam, not closing all the way, getting out of time with the crank.

But the other aspect that both 2 and 4 strokes are subjected to is the flow dynamics of the incoming a/f charge and outflow of exhaust, which controls at what rpm the best power is made, and how wide the range in rpm . In either case you are limited to a range in rpm where that fixed port or valve timing works for the engines, go beyond it, they stop breathing as well, power falls off.

Not with a Desmodromic valve train.

 

[bwalker]

Not with a Desmodromic valve train.

Or pneumatics.