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[Field Marshal Dr. Opti]

My petrol mower is powered by a 118cc four stroke OHV engine. It is rated at 3.5 HP. How does this differ from 3.5 BHP.

Does any mechanical boffin out there know?

[millwall]

BRAKE  theres your difference

[cem_devecioglu]

better than I could explain
http://wiki.answers.com/Q/What_is_the_difference_between_hp_and_bhp

[Brikhead]

I'd always presumed that hp (horse power) was just an abreviated version of brake horse power...
Then you have PS and kW...

"Some car manufacturers still quote a power output rating called PS, which stands for Pferdestärke (literally, 'horse strength'). It's alternatively known as DIN (Deutsches Institut für Normung ) hp as opposed to SAE (Society of Automotive Engineers) bhp.

PS is a slightly higher figure than the SAE bhp that we quote, so that's where the discrepancy creeps in.

As a rule of thumb, you can knock off one PS for every 100PS to reach a rough bhp figure. If you want to be completely accurate, multiply the PS figure by 0.9864 to reach the bhp total, or bhp by 1.0139 to get back to PS.

An EU Directive tried to replace the use of PS with kilowatts in the 1990s. One bhp is equivalent to 745.7 Watts, so multiply bhp by 0.7457 to get a kW figure, or kW by 1.341 to do the sum in reverse.

Manufacturers have found that few motorists have any immediate understanding of kW ratings, however, so you're unlikely to see it."

Taken from here...
http://www.whatcar.com/car-news/what-car-q-and-a/what-do-ps-and-bhp-mean/218056

[MaxV6]

Horse Power is the amount of grunt your engine has.


Break Horse power is what TB does to them \

 

[Field Marshal Dr. Opti]

I'd always presumed that hp (horse power) was just an abreviated version of brake horse power...
Then you have PS and kW...

"Some car manufacturers still quote a power output rating called PS, which stands for Pferdestärke (literally, 'horse strength'). It's alternatively known as DIN (Deutsches Institut für Normung ) hp as opposed to SAE (Society of Automotive Engineers) bhp.

PS is a slightly higher figure than the SAE bhp that we quote, so that's where the discrepancy creeps in.

As a rule of thumb, you can knock off one PS for every 100PS to reach a rough bhp figure. If you want to be completely accurate, multiply the PS figure by 0.9864 to reach the bhp total, or bhp by 1.0139 to get back to PS.

An EU Directive tried to replace the use of PS with kilowatts in the 1990s. One bhp is equivalent to 745.7 Watts, so multiply bhp by 0.7457 to get a kW figure, or kW by 1.341 to do the sum in reverse.

Manufacturers have found that few motorists have any immediate understanding of kW ratings, however, so you're unlikely to see it."

Taken from here...
http://www.whatcar.com/car-news/what-car-q-and-a/what-do-ps-and-bhp-mean/218056

Yes . I seem to recall that the BMW M5 was rated at 507 PS......500 BHP

Renault clit 172 (PS).....actually 170 BHP.Confusing.

[Ken T]

When I were but a lad.........

I was taught there were 2 measurements.  1 was IHP or indicated horsepower. This was the theoretical power output, and was equal to PLANK/6*10E4, where the values were pressure, length of stroke, CSA of cylinder, no of cylinders, K a factor for 2 stroke or 4 stroke.

BHP was the actual achievable output, basically the engine turned a shaft with a braking load on it and the more load the engine turned without changing speed or stopping was its BHP. The formula here was 2*pi*N*T/6*10E4, but I can't remember what they stood for.

Ken

[Ian_D]

When I were but a lad.........

I was taught there were 2 measurements.  1 was IHP or indicated horsepower. This was the theoretical power output, and was equal to PLANK/6*10E4, where the values were pressure, length of stroke, CSA of cylinder, no of cylinders, K a factor for 2 stroke or 4 stroke.

BHP was the actual achievable output, basically the engine turned a shaft with a braking load on it and the more load the engine turned without changing speed or stopping was its BHP. The formula here was 2*pi*N*T/6*10E4, but I can't remember what they stood for.

Ken

Hmmm...         *scratches head*

 

Nope, im too tired to even try and think about it...   

[Osprey]

Here's a video of a dyno showing the "brake" from brake horsepower in its crudest form.  Cut to the chase at 2 minutes in part 2:

Prony Brake part 1
Prony Brake part 2

I guess that's how it's done in Illinois 

[Kevin Wood]

Here's a video of a dyno showing the "brake" from brake horsepower in its crudest form.  Cut to the chase at 2 minutes in part 2:

Prony Brake part 1
Prony Brake part 2

I guess that's how it's done in Illinois 

That's exactly the essence of it, IMHO. And exactly the same principle is applied when using a dyno these days. Use a variable brake to apply a load to the engine until it is fully loaded, then  measure the torque (what he was doing with the weights) and the RPM (he had a hand-held tachometer). From that you can calculate the work dissipated in the brake - hence brake horsepower as opposed to any other indicator of horsepower based on a rule of thumb calculation.

[Marks DTM Calib]

HP is the power the engine produces, BHP is the power at the engine output and hence is a more useful figure as the losses associated with running water pumps, alternators etc (e.g. essential house keeping items)are already subtracted from the HP figure.

[Marks DTM Calib]

I should add that on a mower engine, the HP will be pretty much the same as the BHP as there is not much in the way of house keeping devices to operate!

[cem_devecioglu]

Horse Power is the amount of grunt your engine has.


Break Horse power is what TB does to them \