Converting Torque To horse power

[Darin]

I picked up a formula created by another distributor that will let you size up an engine that is labeled with torque power to an approximate horsepower.
Simply take the number of cc's and divide by 29. While it is not the exact horsepower it is accurate enough for a dealer to size up a replacement engine for a repower application.

This is handy since most engines are labeled with cc's anymore!!

 

[FATGUY]

Dyno's don't measure HP

When an engine is put on a dynamometer doesn't actually measure HP, it measures torque. To derive horsepower from torque you would use this formula.
Horsepower = (5252 X torque) / RPM
The OP's formula is great, I just wanted to show how torque and hp are related.

 

[Darin]

Great thanks. I think the distributor was hoping for a quick easy way for cheap counter help to give the customer a round about number. I remember getting the how many horse question a lot and all it had was a cc number listed.

 

[edisto]

Did he specify whether this was for 2-strokes? It's a horrible underestimate for chainsaws, that gets worse as displacement increases.

I pulled some numbers off of Mike Acres site. The relationship between HP and displacement is non-linear, so I transformed displacement by squaring it.

The dots are the raw data points, the broken line is the displacement divided by 29, and the solid line I generated using a simple least-squares linear regression, which resulted in:

HP = 0.000536 * displacement^2 + 1.997

 

[Darin]

Yeah, I think the chainsaw forum wasn't the best place for this as it was more for 4 stroke. I just found it interesting. Thanks for the graph. Pretty interesting.

 

[demographic]

When an engine is put on a dynamometer doesn't actually measure HP, it measures torque. To derive horsepower from torque you would use this formula.
Horsepower = (5252 X torque) / RPM
The OP's formula is great, I just wanted to show how torque and hp are related.

That's the one as the first method doesn't take standard many Japanese sportbike horsepower into account, it does work out not to far from the truth with many standard Harleys though, not quite sure why that is:monkey:

The Horsepower = (5252 X torque) / RPM version also shows that horsepower is just a function of torque and RPM which kind of throws a spanner into the gears of all those long torque versus horsepower threads that turn up on bike and car forums every three weeks along with the oil threads.

 

[Taxmantoo]

I think it's aimed at getting a better number than the current "power number developed at brochure" for stuff like 4 stroke lawnmower engines.

Like when Sears advertises a 20" push mower as having 6.5 undefinable units of engine thrust, but you know it's got roughly a 3hp or maybe 4hp engine on it.
If you were to repower a 8hp tiller with an "8 whatever" engine, it just won't work, but do you need to buy the 12 whatever engine or the 15 whatever engine? OP's formula just ignores the whatever rating and goes by displacement, which is probably wiser than trying to make sense of the rated output of the new engine.

 

[Darin]

That is exactly what it is for!! Just thought it might be handy for an over the counter round about number.

 

[harrygrey382]

Did he specify whether this was for 2-strokes? It's a horrible underestimate for chainsaws, that gets worse as displacement increases.

I pulled some numbers off of Mike Acres site. The relationship between HP and displacement is non-linear, so I transformed displacement by squaring it.

The dots are the raw data points, the broken line is the displacement divided by 29, and the solid line I generated using a simple least-squares linear regression, which resulted in:

HP = 0.000536 * displacement^2 + 1.997

see ya and raise ya -

 

[cuznguido]

Geez fellas, some of us like to hang out here cause there are some really neat folks on here and they hardly ever talk about such stuff as least square linear regression. That's what I'm here to get AWAY from. Let's keep it simple, such as: My Stihl can kick your Husky's ass, or vice versa (exit mumbling--least square linear regression............) :greenchainsaw:

 

[edisto]

see ya and raise ya -

Ooooohhh...lots of data. Very nice. Looks like possibly 2 separate trends.

With all the fuss they make over the 7900, I'd have thought you'd need a taller y-axis.

But where's the regression?

Geez fellas, some of us like to hang out here cause there are some really neat folks on here and they hardly ever talk about such stuff as least square linear regression. That's what I'm here to get AWAY from. Let's keep it simple, such as: My Stihl can kick your Husky's ass, or vice versa (exit mumbling--least square linear regression............) :greenchainsaw:

Sorry...but at SOME point you have to talk about numbers.

 

[TommySaw]

This is why I like that they are moving away from "advertised hp" as it is a quantification of the ability to do work over time, which is nice but Torque is the actual measurement of the turning force of the engine which is allows for a much easier head to head comparison. Torque curve is every bit as important if not more so than hp. The 346xp and 460s engines are a great example of this, both put out identical hp but the torque curve makes them suited to much different tasks

 

[BobL]

Ooooohhh...lots of data. Very nice. Looks like possibly 2 separate trends.

Maybe you re confused between the Squares and triangles OR HP and Torque?

 

[edisto]

Maybe you re confused between the Squares and triangles OR HP and Torque?

It is 2 separate trends! You're right Bob, I didn't realize that HP and torque both were on the same graph.

Half the data I thought there were, but still more than I had!

 

[BobL]

Geez fellas, some of us like to hang out here cause there are some really neat folks on here and they hardly ever talk about such stuff as least square linear regression. That's what I'm here to get AWAY from. Let's keep it simple, such as: My Stihl can kick your Husky's ass, or vice versa (exit mumbling--least square linear regression............) :greenchainsaw:

I'd like to think we are not so monocultural. Some come here to yell "My Stihl can kick your Husky's ass, or vice versa", others to perv at big old saws, some to learn, some to put up inane polls or funny photos, while for a few "a least square linear regression" is a bit of light fun maybe compared to what they do in their day job. Some want to keep things simple, others want to wring out the last 1/1000th of an HP out of their saws, and others want to make it as complicated as possible. We're a very broad church - learn to love us, ridicule us or leave us.

 

[RVALUE]

I was curious about this when I was looking at a Yamaha generator. No where did it mention HP or torque? Finally bought one and it did the job, so it was adequate. If the mfg. lies about the horsepower, then we are chinad.

 

[edisto]

Maybe you re confused between the Squares and triangles OR HP and Torque?

I'm confused again...I think the legend is reversed for Stihl.

Were these numbers measured, or according to the manufacturer? Hard to believe the 090 makes less than 8 HP...I know manufacturers rate high, but that's a 5hp difference.

 

[TommySaw]

I'm confused again...I think the legend is reversed for Stihl.

Were these numbers measured, or according to the manufacturer? Hard to believe the 090 makes less than 8 HP...I know manufacturers rate high, but that's a 5hp difference.

agree looks off

 

[SawTroll]

I picked up a formula created by another distributor that will let you size up an engine that is labeled with torque power to an approximate horsepower.
Simply take the number of cc's and divide by 29. While it is not the exact horsepower it is accurate enough for a dealer to size up a replacement engine for a repower application.

This is handy since most engines are labeled with cc's anymore!!

KW and hp/bhp ("power") is a function of torque and rpm, and has no direct connection to cc.

 

[SawTroll]

see ya and raise ya -

That one is outdated, and there are mistakes as well.......