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Tech
Information
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| What
is horsepower (HP)? |
James
Watt made some pretty hot steam engines before we were born (get the "hot"
pun?). Anyway, he needed a way to measure the power output of them, so
he hooked his horse up to one of those pumps that you turn the lever around
in a circle to make it pump. He did all the math figuring how fast the
horse was going and how much torque it put on the pump over 1 minute,
blah blah, and came up with a horsepower number of 550 pounds per feet
per second.
HP = RPM * torque /5252
RPM is revolutions per minute
Torque is in ft pounds
5252 takes care of converting all the units from Watts' 550 pounds per
feet per second.
By the way, 746 Watts (electrical) = 1hp.
You can fiddle with this formula to solve for rpm or torque too.
example: torque = HP * 5252 / rpm
example: rpm = HP * 5252 / torque
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| What
is BHP or brake horsepower? |
This
is HP measured at the crankshaft of the engine, with no fan, air cleaner,
alternator, transmission, air conditioner, basically nothing but the engine.
This how most manufactures rate their engines, and it is pretty much crapola.
Rear wheel hp (RWHP) is what your making at the wheels, what your putting
to the road, and it should be all you care about, because that is what
moves your vehicle. All our dyno charts are true RWHP. A lot of dyno shops
up the RWHP that they measure by 15-30% (estimating losses of trans, alternator,
whatever), and try and give you an BHP number. Yes, it gives you a bigger
number, and yes, your a sucker to believe it. How do you know if those
power pulleys, new tranny, lightened flywheel make a difference if someone
is fudging your numbers from dyno to dyno? Don't let them do it, and don't
let someone show you a chassis dyno curve that indicates BHP.
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| What
is corrected HP? |
Corrected
Horsepower is a way to equalize dyno readings across temperature, barometric
pressure, and relative humidity. All these conditions affect the way
your car breathes air and makes power. Does your car feel snappier on
a cold day? It's because the air is denser, so your car gets a bigger
gulp of air as compared to a hot day, and makes more power. Ever drive
in the mountains and feel like your car lost 2 cylinders? As you go
up in altitude the air gets thinner, so your car can't get as much air
to make power. Same thing happens to me when I go hiking. Anyway, the
SAE (society of automotive engineers) got together and figured out how
all these factors affect HP, and we can apply some simple math to our
dyno results to "correct" for the atmospheric conditions when
the test was done. If everyone corrects to the same standard conditions,
then we can compare dyno results from day to day. All our dyno charts
are corrected to SAE 29.6"Hg 77 deg F wet conditions.
Thrust = drive wheel torque/rolling radius.
Thrust is pounds, wheel torque in ft pounds, radius is feet, this has
been discussed above.
Everyone asks me for the formula to convert 1/4 mile ET to horsepower.
Here it is....
HP = weight / (ET/5.825)^3
weight is in pounds
ET in seconds
The little ^3 means cubed, ie multiply the ET/5.825 result times itself
3 times.
You can fiddle with this formula to solve for other numbers, like if
you know HP and weight, you can calc what your best ET could be by solving
the formula for ET. If your ET is not close to this number, you need
to call us and get your gearing set up correctly. |
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| More
tech info |
Oxygen
Sensors
Thrust
Horsepower
Conversions |
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1039
riverside street suite10 
