| Author |
Message |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 635
Registered: 4-2002
| | Posted on Wednesday, May 07, 2003 - 9:04 pm: | |
And then there is another kind of HP;
Indicated HP (torque actually) is determined by the HP porduced by each cylinder independently. The way one measures each cylinder independently is by controlling the spark to cylinders independently. The spark to each cylinder is cut at regular intervals in order to measure how much HP is missing (since that cylinder did not produce power). Once all cylinders are accurately measured, IHP = sum(cylinders):
loss = IHP-BHP
IHP tells you things about the combustion process, and the difference between IHP and BHP tells you things about the mecanical efficiency of the motor. |
Mark Eberhardt (Me_k)
Member
Username: Me_k
Post Number: 496
Registered: 5-2002
| | Posted on Wednesday, May 07, 2003 - 6:11 pm: | |
You can use a brake dyno to measure rwHP to. It just means a variable load or brake, often a water pump or magnet on newer units)is being used. Dynojet type dynos are acceleration dynos and calculate hp by measuring the rate the engine accelerates a flywheel (it's f=ma all over again) |
Craig A (Milo)
Junior Member
Username: Milo
Post Number: 84
Registered: 4-2003
| | Posted on Wednesday, May 07, 2003 - 4:25 pm: | |
I've always heard "brake".
http://auto.howstuffworks.com/horsepower.htm
|
Jeff Green (Carguy)
Member
Username: Carguy
Post Number: 261
Registered: 10-2002
| | Posted on Wednesday, May 07, 2003 - 2:53 pm: | |
Yes...it is "BRAKE". A "brake" dyno is used to measure horsepower off the crankshaft. Question...were the belt driven accesories on the motor when this was done (air pump and/or alternator)? Rear wheel horse power is somewhere around 80% to 85% of the crank horsepower, provided the accesories were included in the "brake-crank" test. If they weren't then the rear wheel numbers would be lower yet. With just the engine running at optimum with no parasitic power losses you are measuring "gross" horsepower. With everything bolted up like the engine were installed in the car you are measuring "net" horsepower. And then driveline losses added to the net values are true rear wheel horsepower. Hey Ferrari fanatic...where did you get "bare" from? Was it in a manual that may have been poorly translated? |
Craig Dewey (Craigfl)
Member
Username: Craigfl
Post Number: 588
Registered: 1-2001
| | Posted on Wednesday, May 07, 2003 - 2:46 pm: | |
Actually, BHP doesn't necessarily mean measured at the crank. It comes from the old method of measuring power that use a Prony Brake which was a tensioned band on the outside of a wheel/cylinder as a retarding torque.
And then there is all the controversy with manufacturers ratings as to what does the rated HP include --- alternator running at what amperage, fan, oil pump, yada, yada, yada... |
Alex Lee (Alxlee)
Junior Member
Username: Alxlee
Post Number: 102
Registered: 4-2002
| | Posted on Wednesday, May 07, 2003 - 2:34 pm: | |
BHP = Brake Horsepower = Power measured at crank
RWHP = Rear Wheel Horsepower = Power measured at rear wheels (dyno/what's actually put down post drivetrain loss)
1 Horsepower = Raising 33,000 lb 1 foot in 1 minute (33,000/60=550)
Or according to Websters:
A unit of power equal in the U.S. to 746 watts and nearly equivalent to the English gravitational unit of the same name that equals 550 foot-pounds of work per second |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 632
Registered: 4-2002
| | Posted on Wednesday, May 07, 2003 - 2:21 pm: | |
Brake! |
TomD (Tifosi)
Advanced Member
Username: Tifosi
Post Number: 3534
Registered: 9-2001
| | Posted on Wednesday, May 07, 2003 - 1:41 pm: | |
p - http://kennedyp.iccom.com/pat/what_is_hp.htm |
Ernesto (T88power)
Intermediate Member
Username: T88power
Post Number: 1465
Registered: 2-2001
| | Posted on Wednesday, May 07, 2003 - 1:36 pm: | |
brake. |
P. Thomas (Ferrari_fanatic)
Junior Member
Username: Ferrari_fanatic
Post Number: 199
Registered: 4-2003
| | Posted on Wednesday, May 07, 2003 - 1:35 pm: | |
No Tom, it is bare not brake. |
P. Thomas (Ferrari_fanatic)
Junior Member
Username: Ferrari_fanatic
Post Number: 198
Registered: 4-2003
| | Posted on Wednesday, May 07, 2003 - 1:34 pm: | |
Bare |
TomD (Tifosi)
Advanced Member
Username: Tifosi
Post Number: 3533
Registered: 9-2001
| | Posted on Wednesday, May 07, 2003 - 1:34 pm: | |
brake |
noel smith (Noel)
Member
Username: Noel
Post Number: 268
Registered: 2-2003
| | Posted on Wednesday, May 07, 2003 - 1:32 pm: | |
I know the (H)horse(P)power part, but what does the "B" stand for in BHP? |