026 Dyno Test

[Gypo Logger]

Hi There, I have a Walkerized 026 Arctic that has been tested on a dyno. I dont understand the corelation between rpm, torque and hp. Could you saw racers, Jon, Ken, Mike, Robert etc. explain to me how these factors affect one another?
I cant believe this saw. It has gained almost 1hp after tuning. The solid line is the tuned saw and the dotted line was the same saw but stock. I dont understand why the saw has the most torque and rpm when at 10,000 rpm.
John

 

[Gypo Logger]

Heres the data for the tuned 026.
John

 

[HUSKYMAN]

Im no expert but most modern saws are designed to peak at 9-11000 rpms, because that is the speed at which the cutting is done. No one cuts at 14000 rpms. My Husky is rated at 9000 I believe

 

[Gypo Logger]

Hi there Huskyman,I understand that the rpm in the cut is alot slower than the rpm out of the cut, but I dont understand how the load is determined when putting a saw on a dyno. Regardless, the saw really is a screamer and may outcut a stock 372 in a cordwood cutting bee (-:
John

 

[motorhead]

Hello John, I'll try to answer your questions regarding dyno testing and the relationship of torque, horsepower and engine speed (in rpm's). First some deffinitions. Engine speed in rpm's is pretty well understood - it's the speed of the motor in revolutions of the crankshaft per minute. Torque is a twisting force and is a measured quantity and is equal to the applied force multiplied by the distance from the center of rotation at which the force is applied (called the moment arm - also called a lever arm). Therefore, 20 foot pounds is equal to 20 pounds of force applied at a distance of 1 foot from the center of rotation. The same 20 foot pound torque can also be obtained with a 10 pound force applied 2 feet from the center of rotation. Horsepower is a measure of the ability to do work and is a derived (or calculated) quantity. I don't have the formula handy, but basically horsepower is equal to a fixed number (a constant C) multiplied by the torque (T) multiplied by the engine speed in rpms' (rpm). So HP = (C) X (T) X (RPM). From this equation, you can see that the same torque produced at a high engine speed produces more horsepower than the same torque produced at a slower engine speed.

An engine dyno is basically a dynamic torque measuring device. It is coupled to the crankshaft (or in the case of motorcycles it is often driven by the rear wheel of the bike). The engine is run at wide open throttle (WOT) and a brake is applied by the dyno to obtain each engine speed at which the torque is to be measured (for example 0 to 14,000 rpm's in 500 rpm increments). When each preselected speed is reached and stabilized, a torque reading is taken by the dyno by means of a torque transducer which is normally coupled to the input shaft of the dyno. From each measured torque reading, the horsepower is calculated and recorded by the dyno and you end up with a data table of torque and horsepower for each selected engine speed. Normally the graph of horsepower and torque is plotted versus engine speed (rpm's) not time as your graph shows. Some relationships you will notice when looking at 2 stroke engine dyno charts (at least all of them that I've ever looked at) is that the torque will always peak (reach maximum) at a lower engine speed then the horsepower (approximately 2,000 to 3,000 rpm's earlier). Peak horsepower is reached at a higher engine speed but with a lower torque since the higher engine speed offsets the lower torque (remember HP=(C) X (T) X (RPM)). The engine speed at which the horsepower peaks has nothing to do with the maximum no-load rpm that the chain saw manufacturers provide - the max no-load rpm is simpley the fastest engine speed that the engine can be run at safely. The engine speed at which peak horsepower occurs will always be significantly earlier than the maximum no-load engine speed. It would be better if the chainsaw manufacturers provided the engine speeds where the horsepower and torque peak since they are more useful numbers - that's what the motorcycle and snowmobile manufactures do.

For a given engine, the engine speed at which the horsepower and torque peak is determined by how the engine is tuned - port timing, exhaust pipe tuning, carburetor size (flow rate), compression ratio, etc. Chain saw motors are tuned to reach peak horsepower at approximately 9,000 to 11,000 rpm which is close to the maximum safe operating speed for an air cooled two cycle motor for sustained use while still maintaining acceptable engine durability. The high engine speed provides for higher horsepower which is used to provide faster cutting speeds. Hope this helps.

Steve

 

[Fish]

Dang Steve,
That is one fine post! Could it be safe to assume that Husqvarna
and Jonsered's high no load rpm specs are just hype to make
people think that their product must be superior? Ok Poulan
Pro too?
I like a good, well thought , educated answer, and yours
qualifies.
Are you just an engineer that dabbles in small engine chat, or
someone that works in the industry? Either way, your posts are
needed here.
This forum has blossomed here in the past week or so, and
a lot of good info is being posted on the web.
If you are in the industry, please e-mail me at [email protected]
as I would welcome your correspondance.
Fish

 

[Gypo Logger]

Hi Fish, I was thinking the exact same thing about high rev claims.
Maybe will higher available no load RPM there is more brake test hp, where torque, hp and rpm meet a happy blend when in the cut.
Steve has really done his homework, and I think the only other person that has defined the 2 cycle condition as well is Johnny Scales of Possum Flats Alabama. Where is Scales anyway?
John

 

[Fish]

He is probably out bass fishing again with that woman again!
I have lost her picture and would like to see her again.
Fish
I think my wife deleted it.

 

[kdhotsaw]

Motorhead

Hi Steve,
Really great dissertation on Torque, Horsepower, and rpm. I've talked to steve a couple of times and he really knows his two cycle engines. and yes as you have already figured out he is a mechanical engineer. we need his input on the tecnical questions
ken dunn

 

[Dennis]

Steve...thanks for that explanation...I have copied and pasted it into my little book of notes that only I will ever understand...as noone else can read my writing...I have pages scribbled full of notes from each time I talk to Ken, another information warehouse...

keep it coming

Fish, i think you will probably find that picture on johns fridge held up by a powersaw magnet....

 

[Fish]

Lambert sent me the picture of the bass again, if I could just
figure out how to crop that woman out of the picture I would
be happy. I knew Steve was probably an engineer, just trying to
figure out what denomination. I majored in Physics myself, along
with a half of a dozen other majors, but was too drunk and
horny to learn much. I like a good post though, Ol Walt is a
champ in that dept as well.
Fish

 

[Mouse trap Engineer]

Howdy Guys,

I will also congratulate Steve on a well written and explained post concerning the 2 stroke air pump. I have a couple of interesting thoughts but am rushed at the moment and will share them later, I am currently fitting a rather large sleigh with a couple new power plants and have a dec 24, deadline.


Johnny Scales

 

[Gypo Logger]

Hi There, good to see you around Johnny, I will look for the post you made some time ago on TSF before we all got thrown off. I save it on what is now my kids computer. This may save you time by not having to type it over again.
Robyn the house wench will want to post here when she gets back, I know for a fact she will want to attend the Clearwater Revival with us all. She is supposed to clean my house when she comes over, but she just sits back at this computer and orders me around with house cleaning instructions, so I guess I am just a kitchen *****.
Anyway, I have learned with digital photography that lighting is everything, and the more natural the light the better. Also a tripod will make a picture very clear if the light is right. I just bought a Sony CD300 that has a 8cm rewrittable disc, but I find I enjoy using the floppy format of the Sony MVC FD88., which is faster and more user friendly. I regret not getting the Sony FD92.
Any picture on the net can be saved by right clicking on it, then click save as, then 3 1/2 floppy. The picture will be saved on your floppy and can be attached when you click the browse button here, but I have noticed that the picture will get lost if you preview it, so just click post reply.
Any online picture can also be posted by right clicking on the picture, then click properties, then copy the picture url, which will always start with http: Then paste this to the text of your post and it will make a clickable link, but dont preview the message or it gets lost. So as we can see we can all post pictures even if we dont have a camera.
I am sorry for not staying on topic, but a picture is worth a thousand words and is a great way to convey what we want to say.
John

 

[dbabcock]

The equasion is: HP=T X RPM/5252. What this means is that with any engine, HP will always be less than T below 5252 RPM. HP will always be greater than T above 5252 RPM. HP will exactly equal T at 5252 RPM. This, of course assumes we are referring to the scalar quantities as referenced to Torque measured in ft.lb.

 

[Gypo Logger]

I was looking for a post Johnny Scales made some time ago about the two cycle airpump theory. Does anyone remember where it is?
Gypo

 

[eyolf]

I haven't seen the "two-stroke as an air pump" post, but there are others that have used that analogy. Basically any engine is just an air pump, but unlike the air compressor you use to fill your tires, the power comes from burning a fuel inside it and temporarily harnessing a small portion of the energy released.

Motorheads excellent post was absolutely true, with one exception: he made it too easy for the reader to infer that only 2 strokes exhibit certain characteristics:

Some relationships you will notice when looking at two-stroke dyno charts

when most gasoline engines do.

An interesting and useful point that hasn't been mentioned is that the torque peak of any engine will also be the point at which it exhibits the best volumetric efficiency...the cylinder is being most completely filled with dense fuel mixture, and if the engine is fairly well matched to application, will do the most work. That is to say, if your truck engine's torque peak is, say, 3200 rpm, that's what you want to shoot for when pulling a heavy load. If your chainsaw's peak is at 9K,...you get the point.

If one looks closely at John's graphs of the modified 026, part of the real value of Walker's mods lies in the fact that increases are realized, but just as importantly, there is a noticeable flat spot in the torque curve. That flat spot is useful, as it affords a great deal of flexibility in use...the chainsaw isn't "pipey", doesn't "fall off" the porting quickly.

I have no college degrees whatsoever; I lacked the patience and finances to see it through. a former girlfriend's family labelled me a "functionally illiterate rustic" for that reason. I seem to have gotten by just fine, however.

 

[porkuface]

Hello gypo logger. The mouse trap engineer has no posts that talk about this. But you have a post that calls out similar things.

http://207.44.158.62/~admin4/showthread.php?threadid=2233

 

[Acer]

Originally posted by motorhead
The high engine speed provides for higher horsepower which is used to provide faster cutting speeds. Hope this helps.

Steve

Interesting post, Steve. It seems the trend in engine design is for ever increasing RPM. Correct me if I'm wrong, but I feel that manufacturers push up the RPMs to ultimately increase power to weight ratio of the machine in question. A faster revving engine producing less torque could supply the same power as a slower, torquier unit - if the engine supplies less torque, the components are put under lower forces, and can be made much lighter.

 

[Gypo Logger]

Hoping to bring back "The Mousetrap Engineer."
John

 

[Gypo Logger]

"functionally illiterate rustic"
Nothing wrong with that Eyolf.
John