A Lesson in Engine Terminology: Powerbands

[SpeedyManiac]

Hi all,
For the past 4 years I’ve been at the University of Alberta studying Mechanical Engineering. During my studies we’ve covered quite a few topics regarding engines and I thought I’d share some of the stuff I learned and hopefully clear up some misconceptions made by a lot of newbies. Please point out any errors in my descriptions, as I make mistakes too.

Most of you (probably all if you’re part of this site) enjoy the rush twisting the throttle and zooming across the dirt. If you have ever ridden a two-stroke, you’ve felt the ‘hit’ when the powervalve opens, which is basically a sudden increase in power. Many people refer to this as the powerband of a bike. This is wrong. Another misconception is only racing bikes have a powerband. I made this mistake too when I was first introduced to bikes, but have since learned the proper definition.

The powerband of an engine is defined as the range of engine speeds between peak torque and peak power output. Below I’ve shown the torque and power curves for 4 bikes. Thanks to DirtRider for the chart.

Now, to effectively ride a bike, you want to stay in the powerband. Ideally, you should use the clutch and gears to keep the engine just past the peak torque RPM, so that when you hit a hill or something requiring more torque, you will naturally have more torque as you slow down slightly. When you get to an RPM below the peak torque value, you have to downshift or slip the clutch in order to get the engine back to the peak torque value.

The coloured arrows below the chart are representing the powerbands of each bike. As you can see, the four-strokes have longer powerbands than the two-strokes. This makes the four-strokes easier to keep in the meat of the power and results in quicker acceleration.

Hopefully that clears up a little bit of the misconception behind powerbands.

 

[oldguy]

Hopefully that clears up a little bit of the misconception behind powerbands.

So how does putting in a purple one work or is the Chucktanium one still the best ;) :)

Now hopefully your post will draw out real questions and help educate some of the newbies :cool:

 

[SpeedyManiac]

Well, I heard Bubba likes the chucktanium one best, so who am I to argue with that. :laugh:

 

[BSWIFT]

Well, at least my red, white, and blue powerband is patriotic!:)

 

[150rguy]

Cool post.

 

[Tony Eeds]

So how does putting in a purple one work or is the Chucktanium one still the best ;) :)

Chucktanium :cool: Anyone that rides my KTM 200 is amazed at the power. I attribute it all to my Chucktanium powerband.

Now hopefully your post will draw out real questions and help educate some of the newbies :cool:

:nod:

 

[Oldman125]

Drag race engines use the power band as much as motocross bikes. Well, bikes race from obstacle to abstacle so its a similar circumstance.
The drag engine is launched at near peak torque off a trans brake and a loose converter to get it rolling and then kept around peak HP by way of a built automatic or a 5/6 speed manual trans. The plan is to shift just after HP tops out and use the gear spread to allow the RPM to only drop a few below peak HP. The tuner then specs gear ratio and tire diameter to match ETs and length of track so that RPMs top out just over peak at the lights.
Power band can be determined by the inlet port size, piston speed (determined by rod length and stroke) cam duration and lift plus bore and stroke and exhaust pipe diameter and length. Simply changing carb size and/or cam profile can change where the power is or where peak efficiency occurs. Most commonly peak fuel efficiency is where peak VE is and tuning the engine combo to the RPM and speed you wish to operate at will net the best fuel milage. (as if we care about that!)
The difference btw drag and MX would be that MX is more demanding by nature such as a road race engine would require. Longer spread (different cam and intake specs) and fatter/longer torque curve necessary.
Not really a tech post, but my thoughts in relation to your topic. I just find all of this interesting.

 

[02yz426f]

Whats peak "VE"?

 

[Moose]

Thanks a lot for posting. I've read it over 3 times now. Interesting stuff.

:cool:

 

[4thGearAndPinned]

so you mean when the hp starts increasing faster than the torque, that is the powerband?

I knida like the old way of thinking, then some bub comes in spreading all of his propaganda, i just don't know.

 

[kmccune]

Silly me, I thought it was the rpm "band" that had the most power! ;)

 

[FruDaddy]

so you mean when the hp starts increasing faster than the torque, that is the powerband?

I knida like the old way of thinking, then some bub comes in spreading all of his propaganda, i just don't know.

Nothing like a heaping teaspoon of correctness to ruin you day, huh?? :nod: I don't know about HP increasing faster than torque, but have you ever notice on a dyno chart that the HP and torque are the same at 5252 rpm. This is because HP is a product of torque. The formula for HP is torque*rpm/5252.

It has been a bit since VE has come up in my little world, but I seem to recall it is volumetric efficiency, deleted

 

[Solid State]

I also learned that 4 strokes do not have powerbands (no power valves to connect them to) and therefore are not Chucktanium-able and suck.

It's true.

 

[WaltCMoto]

Im still waiting to recieve mine (power band) in the mail. I ordered them from Oldguy last April. :whoa:

 

[oldguy]

Im still waiting to recieve mine (power band) in the mail. I ordered them from Oldguy last April. :whoa:

well we have had a bit of trouble getting enough unobtainium to make one for you. If you can just wait as patiently as you have been I think there is a chance that a new source is about to be located

 

[Oldman125]

VE relations can be described as: The amount of air/fuel an engine can suck in vs. how much that engine should be able to suck in mathematically.
Here is a link to an easy read. It is actually an aviation thread, but a piston engine none the less.
http://www.eaa1000.av.org/technicl/engemp/engemp1.htm

 

[2stroke]

Hi all,
If you have ever ridden a two-stroke, you’ve felt the ‘hit’ when the powervalve opens, which is basically a sudden increase in power. Many people refer to this as the powerband of a bike. This is wrong.

Neat information, I never knew the actual definition.Very Cool. I have a few questions though......

That period in time when you feel the "hit"... arent you feeling the point that you described between peak torque and RPMs? Torque is something that you can feel when riding. Imagine that range when torque is reaching it's greatest point, along with the RPMs peaking....think of that in terms of what the rider will feel....So in a way, I would say that the hit you describe is the powerband, or rather what the riders feels because of it?

I have a '75 MX400 that is VERY peaky. It has a light switch "hit" that will rip your arms out in whatever gear you gas it in...and it has no powervalve at all. So the "hit" does not necessarily have to do with the powervalve.

Although, I would expect the powervalve to come into play if so equipped, at or shortly before the point that the RPMs are reaching peak range so it is probably also coincidentally accurate to say that when the power valve opens, you are in the power band....?

 

[SpeedyManiac]

Yes, you are right. I've been thinking about it and have a tough time explaining powervalve function as I'm not completely sure on its workings. Rich can probably give a better explanation.

Here's my understanding though:
The powervalve is used to widen the powerband on two-strokes. It operates by changing the exhaust port size at a certain RPM. At low RPMs, a smaller exhaust port means more power, but once the engine gets to a certain RPM, the powervalve opens, increasing the exhaust port size, letting more exhaust gases flow out faster, increasing power. There is a jump in torque when the bike opens the powervalve, so you feel a 'hit.'

Non-powervalved two-strokes are generally peakier (a feel like they hit harder) because the bikes run poorer than their powervalve equipped brothers. When they start running well (exhaust port size is matched to RPM, engine load and throttle position), they come on strong.

So, in summary, I may be wrong saying the powerband starts when the powervalve opens. It depends on the individual bike.

Sorry if I'm not making sense, spent most of the day in class, then working on homework, then fixing up some pictures for some photo contests and stuff, and then I came to check DRN. My brain is toast at the moment.

 

[CaptainObvious]

So how does putting in a purple one work or is the Chucktanium one still the best ;) :)

Now hopefully your post will draw out real questions and help educate some of the newbies :cool:

Dave,

It took you 2 hours and 13 minutes to derail this thread. You're slowing down :rotfl:

 

[2stroke]

I also have an old Kaw 2 stroke (F9-350) that makes all its power down low...it's a stump puller, broad and even with a little bit of a "hit" at midrange....but it doesnt wind out like the mX400.

I think as far as powerbands go, my favorite was that of my '93 KX250. It was easy to make the power...there was no lag...no dead spots. It took off with a nice grunt and lit up easy.

I guess Im starting to think about the powerband as a snowball rolling down a hill you know. Just that sweet spot where the grunt and the scream work together! :rotfl:

ITs really neat how bikes vary. Its like guitars, some people would think they are all the same, but they all have their own personality. (And like guitars, you cant own too many bikes!)

 

[DougRoost]

Im still waiting to recieve mine (power band) in the mail. I ordered them from Oldguy last April. :whoa:

You should have ordered them here: Click link
While you're at it, pick up a set of their cross-drilled brake lines! :)

 

[m4i2k2e2]

so you mean when the hp starts increasing faster than the torque, that is the powerband?

I knida like the old way of thinking, then some bub comes in spreading all of his propaganda, i just don't know.

same.

 

[D Lafleur]

Yes, you are right. I've been thinking about it and have a tough time explaining powervalve function as I'm not completely sure on its workings. Rich can probably give a better explanation.

Here's my understanding though:
The powervalve is used to widen the powerband on two-strokes. It operates by changing the exhaust port size at a certain RPM. At low RPMs, a smaller exhaust port means more power, but once the engine gets to a certain RPM, the powervalve opens, increasing the exhaust port size, letting more exhaust gases flow out faster, increasing power. There is a jump in torque when the bike opens the powervalve, so you feel a 'hit.'

Non-powervalved two-strokes are generally peakier (a feel like they hit harder) because the bikes run poorer than their powervalve equipped brothers. When they start running well (exhaust port size is matched to RPM, engine load and throttle position), they come on strong.

So, in summary, I may be wrong saying the powerband starts when the powervalve opens. It depends on the individual bike.

Sorry if I'm not making sense, spent most of the day in class, then working on homework, then fixing up some pictures for some photo contests and stuff, and then I came to check DRN. My brain is toast at the moment.

Very close in your thinking. The powervalve, helps to shape the power curve, by varying the VE of the engine as RPM is increased. It is a tuning device, similar results to VVT in 4 stroke engines.

Now if I could just figure out why my RM 250s do it so much better than my other bikes, I would be happy. I have accepted the fact it is due to the "yellow Powerband" that Suzuki puts in it at the factory. :)