Abby’s Guide > Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) > Discussions > Does HP Matter?
Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions |
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royster
" It is the use of power tools that separates man from animals"
Location: New Brunswick, Canada
Joined: Feb 11, 2011
Points: 284
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Re: Does HP Matter?
Reply #12 Nov 10, 2011 4:06 pm |
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I believe that the Briggs engines are an excellent choice. The 305 with 14.5 torque for blowers up to 27 inches. and the 342 with 16.5 torque for blowers over 27 inches. I am referring to the engines built in the USA and they are stamped as built in the USA. But it seems that the 305 and 342 engines (and other sizes) labelled "Polar Force engines By Briggs " are manufactured in China. If anyone has other information on these Polar Force engines., please reply. Thankyou
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coasteray
El Toro! 1028 LXE
Tecumseh 358cc
10hp
Location: NE Washington State
Joined: Mar 3, 2008
Points: 142
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Re: Does HP Matter?
Reply #13 Nov 11, 2011 1:42 am |
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Well, there's the formula most of us know about: Horsepower = torque (in ft-lbs.) x rpm (typically 3600) 5252 Thus, if you have a 305cc engine with a 14.50 torque figure, it comes out: HP = 14.5 x 3600 = 9.94
5252The 5252 is a real figure, not just something made up to make us happy: http://www.epi-eng.com/piston_engine_technology/power_and_torque.htmSee the end section of the article entitled " Derivation of the Power Equation (for anyone interested)". It explains how the number 5252 is arrived at. Very interesting.
Rearranging the formula gives us :
Torque = Horsepower x 5252
rpm (typically 3600)
So, if you have an engine like the 10HP Tecumseh 358cc on my El Toro! 1028LXE, it looks like this: Torque = 10.0 x 5252 = 14.58
3600
Do these figures seem good, realistic? I think so. The only thing I'm not sure about is that I've read that torque is supposedly measured at 3060rpm instead of 3600rpm. Assuming that's the case, then how could we plug in a torque figure based on 3060rpm into a formula assuming 3600rpm, and expect a decent result? That would change the above horsepower formula to a higher final result, assuming the torque keeps climbing all the way to 3600rpm. Doesn't it peak out before that on these engines? The torque formula is based on 3600 since we didn't start with a torque figure to begin with, so my result of 14.58 ft-lbs for my Tecumseh engine is based on the horsepower figure and 3600rpm. And we assume horsepower is calculated on 3600rpm, anyway, so that 14.58 torque number seems to be right. Also, assuming that a 358cc L-Head is equal in torque/horsepower to a 305cc OHV, that 14.58 is mighty close to the 14.50 figure we get from today's Briggs 305cc engines. After all, the Briggs 305cc replaced the Tecumseh 358cc on the Toro 1028 (LXE going to OXE). I hope I'm not losing anyone on this. I find it interesting.
This message was modified Nov 18, 2011 by coasteray
 El Toro! 1028 LXE - Tecumseh 358cc 10hp Let it snow! Let it snow! Let it snow!
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manjestic
Location: North Shore, MA
Joined: Oct 31, 2011
Points: 87
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Re: Does HP Matter?
Reply #15 Nov 11, 2011 9:35 am |
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Do these figures seem good, realistic? I think so. The only thing I'm not sure about is that I've read that torque is supposedly measured at 3060rpm instead of 3600rpm. Assuming that's the case, then how could we plug in a torque figure based on 3060rpm into a formula assuming 3600rpm, and expect a decent result? That would change the above horsepower formula to a higher final result, assuming the torque keeps climbing all the way to 3600rpm. Doesn't it peak out before that on these engines? The torque formula is based on 3600 since we didn't start with a torque figure to begin with, so my result of 14.58 ft-lbs for my Tecumseh engine is based on the horsepower figure and 3600rpm. And we assume horsepower is calculated on 3600rpm, anyway, so that 14.58 torque number seems to be right. Also, assuming that a 358cc L-Head is equal in torque/horsepower to a 305cc OHV, that 14.58 is mighty close to the 14.50 figure we get from today's Briggs 305cc engines. After all, the Briggs 305cc replaced the Tecumseh 358cc on the Toro 1028 (LXE going to OXE). I hope I'm not losing anyone on this. I find it interesting.
Careful. HP is a function of RPM and torque at that RPM. And peak torque and peak HP rarely, if ever occur at the same RPM. Many times the peak torque occurs well below 3600 RPM. See the example chart above. I don't know what constraints manufacturers are under when reporting torque. Probably, they can report peak torque at whatever RPM it occurs. So, as you essentially state, it is key that you know at what RPM your torque value occurs. Then you can calculate the HP at that RPM, but not necessarily peak HP. If you know that your 14.5 torque is at 3060, then your HP is 8.44 at 3060. Peak HP may be higher at 3600 RPM. You appear to come to the same conclusion.
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), HP is (was) a sales gimmick. And newbies better learn fast because since they lost that court case the manufacturers aren't spouting horsepower numbers anymore. Now it seems like they are advertising displacement, as if more displacement means you'll get more power - you might, but it's not directly related.
