Originally posted by "The^Thief"
Originally Posted by speed_daemon1
as goofy as this sounds, I have personaly whitnessed it.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?
My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.
This should help claify that Dyno's don't meausre HP they measure torque and use that to create a HP curve.
Measuring Horsepower
If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. Horsepower is pure theory--it's an arbitrary number. A dynamometer places a load on the engine and measures the amount of TORQUE that the engine can produce against the load. Some dynamometers measure the acceleration rate of a known mass at a given rate of speed--like a DynoJet. The basic formula used is:
Force (ft/lbs) = MASS (lbs) X ACCELERATION (ft/second)
Since the MASS of the roller is known, and the ACCELERATION rate can be measured with simple sensors, the Force exerted on the roller in "ft/lbs" is then measured. With in input from the engine such as RPM--we then input the data and make up "horsepower". There are other correction inputs like atmospheric pressure, humidity, etc...but we won't go into that here. The formula most widely accepted becomes:
Here's more info on this:
http://www.eidnet.org/local/westers_garage/horsepower.htm
I agree with you completely, I just don't understand how the damn thing can create a hp curve with out spark and not a tq curve?
Obviously it doesn't reference the curve against rpm, it does it against mph.
However I have seen dyno charts against rpm where the tq curve has spots where it completely dissapears, John says that happens when the inductive pickup isn't reading any spark, but the hp curve continues on a normal path.