# Old hp vs. new cc rating?



## bwright1818 (Dec 2, 2014)

What's the relationship? Surely the new cc ratings must translate into a rough hp rating?


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## mrsteve7 (Sep 2, 2015)

I have heard roughly 30cc per HP as a "ballpark" figure.


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## micah68kj (Oct 8, 2011)

Maybe this will help?
Small Engine Cubic Centimetres (cc) to Horse Power Calculator


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## uberT (Dec 29, 2013)

Isn't it easier to work backwards from the torque value to arrive at hp? Don't these motors generally operate at 3600 rpm?

*HP* = _*Torque*_ x RPM ÷ _*5252*_.


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## Cardo111 (Feb 16, 2015)

Unfortunately there is no accurate way to convert cc's to engine power. Since the lawsuits years ago where manufacturers overstated HP many companies likely in fear of litigation against them have moved to cc's. Briggs and LCT are among the few to state torque ratings which is an accurate measure of power. I attached a previous thread on this forum that also addressed this.


http://www.snowblowerforum.com/forum/general-snowblower-discussion/66537-how-relevant-ccs.html


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## Town (Jan 31, 2015)

Ariens rates my 414 cc LCT engine at 20 ft lbs of torque and 12.5 HP at 3600 rpm based upon the model/serial number definition, etc in my owner manual. 

The 30 cc per HP rating gives 13.8 HP. 

The torque rating calculation (HP = Torque x RPM ÷ 5252) gives 13.7 HP = 20 ft lbs X 3600 ÷ 5252 where 20 ft lbs is the Ariens/LCT torque for the 414 cc engine and 3,600 is the rated engine speed at that max HP.

The web based calculation of HP based upon CC gives 12.7 HP for the same above engine.

Good luck with that.


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## bwright1818 (Dec 2, 2014)

That's all interesting stuff. I'll squirrel it away until I need it. Thanks to everyone!


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## ELaw (Feb 4, 2015)

Cardo111 said:


> Briggs and LCT are among the few to state torque ratings which is an accurate measure of power.


Actually for what it's worth... torque is no more or less accurate a measure of power than horsepower... *if* an RPM figure is given with the torque figure which it usually is not.

As others have posted, horsepower is just torque times RPM times a constant. If you have an accurate figure for torque at a particular RPM, you can accurately calculate HP at that RPM. If you do not have the RPM associated with a torque number, it's meaningless!

I actually think in a way the manufacturers are being deceptive with the torque figures. For example, the Briggs 1450 series of engines is rated 14.5 foot-pounds of torque. Most of us here would assume that since such an engine typically runs at 3600 RPM, it should make 14.5 (ft-lb) * 3600 (RPM) / 5252 = 9.9 horsepower.

But if you look on Briggs' website (Engine Horsepower & Torque Value | Briggs & Stratton FAQ), you'll see that torque figures for most of their engines are quoted at *3060* RPM, not 3600. Using that value, the calculation becomes 14.5 * 3060 / 5252 with the result being 8.5 horsepower... at 3060 RPM. There's no way of knowing what HP the engine makes at 3600 RPM since no torque figure is given for that RPM. And torque varies over RPM so you can't assume the 3600 RPM torque is the same as the 3060 RPM torque... the torque at high RPM is almost always less.


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## Loco-diablo (Feb 12, 2015)

Wow.. this thread gave me headache! LOL!


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## Cardo111 (Feb 16, 2015)

ELaw said:


> Actually for what it's worth... torque is no more or less accurate a measure of power than horsepower... *if* an RPM figure is given with the torque figure which it usually is not.
> 
> As others have posted, horsepower is just torque times RPM times a constant. If you have an accurate figure for torque at a particular RPM, you can accurately calculate HP at that RPM. If you do not have the RPM associated with a torque number, it's meaningless!
> 
> ...


We agree to disagree as twisting force at the PTO is a good indication of how powerful an OPE engine is. While the torque spec given by LCT or Briggs may very well be the peak rating it is still more accurate than horsepower which was left up to the manufactures to rate themselves, hence the lawsuits. I believe there should be a standardized system for consumers to make more informed decisions. However trying to predict horsepower solely based on specs/ a formula is certainly not accurate, as we all know a Honda 270cc engine is going to be more powerful than a 270cc or similar sized Powermore engine.


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## Kielbasa (Dec 21, 2013)

How many pints in a quart? :icon-hgtg:


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## detdrbuzzard (Jan 20, 2012)

" we all know a Honda 270cc engine is going to be more powerful than a 270cc or similar sized Powermore engine. "
that could be a false statement but we don't have proof either way but I think the Honda will be more dependable and most likely more durable engine


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## GustoGuy (Nov 19, 2012)

detdrbuzzard said:


> " we all know a Honda 270cc engine is going to be more powerful than a 270cc or similar sized Powermore engine. "
> that could be a false statement but we don't have proof either way but I think the Honda will be more dependable and most likely more durable engine


More efficient overhead valve design on the newer engines are about 10% to as much as 15% more powerful per cubic centimeter then the old flathead engines were. I have 3 Harbor Freight predator 212cc engines and they can be souped up to as much as 15 horsepower through NR racing with their stage 4 kit. Souped up predator 212cc have ran with genuine Honda 196 cc engines and even beat them due to their slightly larger displacement and slightly longer stroke. These engines are the darling of the carting world and there's lots of high performance upgrade parts for these engines.


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