Abby’s Guide > Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) > Discussions > Converting cc's to HP  A Rough Formula
Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions 

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 online 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

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/Snowblowerpowerratings". The post was dated October 11, 2009. None of this stuff is official, of course! Based on the 20102011 Ariens fullsize 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: 2388


Re: Converting cc's to HP  A Rough Formula
Reply #3 Oct 7, 2011 12:29 pm 

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/Snowblowerpowerratings". The post was dated October 11, 2009. None of this stuff is official, of course!
Based on the 20102011 Ariens fullsize 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 (Lhead) 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 

Assuming this table is for 4 stroke OHV engines. Does this apply to side valve (Lhead) 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/3367101.html
El Toro! 1028 LXE  Tecumseh 358cc 10hp Let it snow! Let it snow! Let it snow!


