horsepower and bhp
Discussion
this thread is nigh on 2 years old and you reply to it? How on earth have you managed that one Neuromancer?mikeylad said:
What is the difference between horsepower and brake horsepower?
Sparks said:
To all intents and purposes, nothing.
The 'brake' part refers to how it is measured (braking the output shaft until it stops and calculating the power from the force required).
I'm sure someone else will correct/explain the above (better).
Horse Power is a measure of the cc. It's a fairly pointless formula and relates primarily to the stroke length, approx 7hp = 1 litre. Nothing to do with bhp.
GetCarter said:
Very slow internet connection in Austria.
GetCarter said:
Very slow internet connection in Austria.
Had a look at sharkyFL's-Profil and didn't notice that the thread was 2 years old, well until now.
Ermmm.. whatever, some informations are just worth to be saved from the digital archives and should pop up every now and then, so we can all remind our self on this old wisdome. Don't you think so? - Question is, if this is one of them? I have my doubts.
p.s.
@ docevi1, so you too read the book?
Lets put this to bed with the facts.
1 horsepower as designated by james watt = 33,000ft/lbs/min via a long calculation its possible to come up with the formula BHP= Torque x revs / 5252
Torque is measurable on some form of brake ie rolling road or dynometer, the dials read bhp because the machine do the calculations for you. All this info is available in various science text books or from any GOOD race engine builder.
(the old method of calculating hp by engine dimensions was used by the RAC for taxation purposes, bore and stroke calculation is history)
Any questions
1 horsepower as designated by james watt = 33,000ft/lbs/min via a long calculation its possible to come up with the formula BHP= Torque x revs / 5252
Torque is measurable on some form of brake ie rolling road or dynometer, the dials read bhp because the machine do the calculations for you. All this info is available in various science text books or from any GOOD race engine builder.
(the old method of calculating hp by engine dimensions was used by the RAC for taxation purposes, bore and stroke calculation is history)
Any questions
If my BHP is measured at a rolling road, then the figure given is at the wheels. If one compares that with the "factory figures" then they were taken at the flywheel.
Therefore to compare like with like it is required to adjust the wheel figure, which will increase the number to account for the power loss between flywheel and rear wheels.
Is my understanding True or False?
Therefore to compare like with like it is required to adjust the wheel figure, which will increase the number to account for the power loss between flywheel and rear wheels.
Is my understanding True or False?
stigproducts said:
If my BHP is measured at a rolling road, then the figure given is at the wheels. If one compares that with the "factory figures" then they were taken at the flywheel.
Therefore to compare like with like it is required to adjust the wheel figure, which will increase the number to account for the power loss between flywheel and rear wheels.
Is my understanding True or False?
True (sort of), most RRs will give you a 'corrected' figure that takes into account the losses. This is only estimated and is usually based on the 'run-down' resistance when finishing the power run. Some RRs are reasonable with these estimates, others may not be so realistic (owners generally want big power numbers so they may over-estimate the losses a bit). As others have commented the manufacturer figures may be when running with no ancillaries at all, therefore higher than you will ever see in the car.
For correcting RR figures in powerful RWD cars the 'rule of thumb' seems to be 15 bhp + 10%, therefore a 250 bhp engine will show around 210 bhp at the wheels (10% of 250 + 15 = 40 in losses).
Hope this helps!
Edited to add: Nice looking Taimar!
>> Edited by kevinday on Thursday 7th April 09:41
andygtt said:
A manufactuer may measure the engine at the flywheel with no auxileries at all, which may result in a signficantly higher figure.
No, this shouldn't happen anymore. Back in the 60's american car manufacturers would quote gross hp by dyno running engines with no ancillaries (water pump, oil pump, alternator, etc) and with no air filters and exhaust systems.
This would give you the absoloute maximum power you could obtain. The reason they did this originally was to inform drag racers how much power could be obtained from any given engine.
However they also did it to look good and to sell cars.
However in Europe we used the DIN standard which measures power at the crank (corrected for drivetrain losses) with the engine installed in the car as it would be used.
In the late 60's legislation was introduced in the States to force car makers to be honest about the power outputs of their cars. This, combined with the new unleaded petrol, made the cars look really puny in comparison with their early 60's musclecars
Nowadays no one should be quoting SAE (gross) figures. It should all be DIN standard net figures.
Unless you're TVR in which case you simply pick any big number you like and stick a hp or lbft sign behind it.
Andy
andytk said:
Nowadays no one should be quoting SAE (gross) figures. It should all be DIN standard net figures.
Unless you're TVR in which case you simply pick any big number you like and stick a hp or lbft sign behind it.
Andy
exactly.... and how many give a different figure for air con or not?
To be hounest though I was thinking more about the claims made by engine builders/tuners and remembering days of old.
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