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FrankMA


Location: Merrimack Valley/Northeastern Mass
Joined: Jul 1, 2010
Points: 587

Converting cc's to HP - A Rough Formula
Original Message   Oct 6, 2011 5:53 am
So I think we all can agree that trying to equate cc's to hp is a PITA and somewhat a hard concept to grasp. I was looking on-line for some sort of conversion tool and came across several formulas that did not make sense to me. They seemed to place the hp ratings much higher for a given cc displacement if you followed the prescribed formula. What I noticed is that they seemed to double the HP rating. Anyway I played around with it a bit and came up with this - it provides a fairly accurate cc to hp conversion without a lot of headaches:

cc displacement (cubic centimeter size of engine) divided by 16 divided by 2

I've tested it out and it seems to be pretty accurate. For example: A Honda 9 HP engine has a displacement of 270 cc's. So... 270 divided by 16 = 16.875 divided by 2 = 8.4375 which is close to the 8.5 HP rating that this engine has historically been rated at in HP.

Another example: A Honda 11 HP engine has a displacement of 340 cc's. 340 divided by 16 = 21.25 divided by 2 = 10.625 which again is very close to the 10.5 HP rating Honda has rated this engine at in HP.

The middle number (16) may have to be increased or decreased based on the size of the engine to get a more accurate estimate.

If for nothing else, it gets you in the ballpark.... Try it out!

This message was modified Oct 6, 2011 by FrankMA


Toro Wheel Horse 522xi GT, Honda HS928TA, Honda HS621AS, Honda HS520A, Toro CCR3000 (work in progress), Honda HS624WA (sold 08/23/2010), Stihl BR550 Backpack Blower, Stihl MS250, McCulloch MS1635, Honda EM6500SX Generator
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epremack


Joined: Feb 24, 2011
Points: 6

Re: Converting cc's to HP - A Rough Formula
Reply #1   Oct 6, 2011 8:31 pm
Assuming this works, it's simpler to just divide displacement by 32.  You'll get the same result and skip a step.
coasteray


El Toro! 1028 LXE
Tecumseh 358cc
10hp


Location: NE Washington State
Joined: Mar 3, 2008
Points: 142

Re: Converting cc's to HP - A Rough Formula
Reply #2   Oct 7, 2011 5:39 am
It might be good to say divide by 32 to obtain the low HP figure, and divide by 28 to obtain the high HP figure, just to be safe, or pick 30 and call it even.  Another option is to take the torque number times 70%.  See "http://www.homekb.com/Uwe/Forum.aspx/repair/67389/Snow-blower-power-ratings". The post was dated October 11, 2009.  None of this stuff is official, of course!

Based on the 2010-2011 Ariens full-size snow blower catalog/brochure, here's what our horsepower figures would look like, using the above numbering schemes:

                                                                                             Horsepower                                                                          
Engine size/Torque              Divided by 32          Divided by 30          Divided by 28           Torque # X 70%
169cc /    ??? ft/lbs                     5.28                         5.63                         6.04                              ???       
205cc /   9.00 ft/lbs                     6.40                         6.83                         7.32                             6.30
249cc / 11.50 ft/lbs                     7.78                         8.30                         8.89                             8.05
265cc /    ??? ft/lbs                     8.28                         8.83                         9.46                              ???
305cc / 14.50 ft/lbs                     9.53                         9.53                       10.89                           10.15
342cc / 15.50 ft/lbs                   10.69                       11.40                       12.21                           10.85
342cc / 16.50 ft/lbs                   10.69                       11.40                       12.21                           11.55
420cc / 21.00 ft/lbs                   13.13                       14.00                       15.00                           14.70

I think this is pretty fun and interesting, though hardly the official word.  However, the range of figures seems reasonable.  Hope you enjoy the little chart.
This message was modified Oct 7, 2011 by coasteray


  El Toro! 1028 LXE - Tecumseh 358cc 10hp   Let it snow! Let it snow! Let it snow!
aa335


Joined: Nov 29, 2008
Points: 2392

Re: Converting cc's to HP - A Rough Formula
Reply #3   Oct 7, 2011 12:29 pm
coasteray wrote:
It might be good to say divide by 32 to obtain the low HP figure, and divide by 28 to obtain the high HP figure, just to be safe, or pick 30 and call it even.  Another option is to take the torque number times 70%.  See "http://www.homekb.com/Uwe/Forum.aspx/repair/67389/Snow-blower-power-ratings". The post was dated October 11, 2009.  None of this stuff is official, of course!

Based on the 2010-2011 Ariens full-size snow blower catalog/brochure, here's what our horsepower figures would look like, using the above numbering schemes:

                                                                                             Horsepower                                                                          
Engine size/Torque              Divided by 32          Divided by 30          Divided by 28           Torque # X 70%
169cc /    ??? ft/lbs                     5.28                         5.63                         6.04                              ???       
205cc /   9.00 ft/lbs                     6.40                         6.83                         7.32                             6.30
249cc / 11.50 ft/lbs                     7.78                         8.30                         8.89                             8.05
265cc /    ??? ft/lbs                     8.28                         8.83                         9.46                              ???
305cc / 14.50 ft/lbs                     9.53                         9.53                       10.89                           10.15
342cc / 15.50 ft/lbs                   10.69                       11.40                       12.21                           10.85
342cc / 16.50 ft/lbs                   10.69                       11.40                       12.21                           11.55
420cc / 21.00 ft/lbs                   13.13                       14.00                       15.00                           14.70

I think this is pretty fun and interesting, though hardly the official word.  However, the range of figures seems reasonable.  Hope you enjoy the little chart.

Assuming this table is for 4 stroke OHV engines.  Does this apply to side valve (L-head) engines as well?
coasteray


El Toro! 1028 LXE
Tecumseh 358cc
10hp


Location: NE Washington State
Joined: Mar 3, 2008
Points: 142

Re: Converting cc's to HP - A Rough Formula
Reply #4   Oct 8, 2011 3:19 am
aa335 wrote:
Assuming this table is for 4 stroke OHV engines.  Does this apply to side valve (L-head) engines as well?

I'm not sure.  Probably not.  I'm assuming it would come out a little less, but maybe it would fit into the low end of the chart. 

Here's another source, based on torque.   Might be a bit more reliable:   

www.abbysguide.com/ope/discussions/33671-0-1.html




  El Toro! 1028 LXE - Tecumseh 358cc 10hp   Let it snow! Let it snow! Let it snow!
Bill_H


Location: Maine
Joined: Jan 12, 2008
Points: 354

Re: Converting cc's to HP - A Rough Formula
Reply #5   Oct 8, 2011 11:15 pm
Not only more reliable, more useful. HP does not really mean anything in snowblowers, since they do their real work under heavy loads. Best to just compare torque values from machine to machine. Don't forget that HP is a made-up sales number based on torque and can vary under different specs. Torque is constant and you can even measure it yourself if you really want to.

Who the hell let all the morning people run things?
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