"Horsepower is to brag about- - - - -torque wins races!" That old adage has been around as long as I can remember, and I started watching my father's dirt track cars at about age 4 in the early 1950's. He tuned his cars on a chassis dyno owned by one of his sponsors, a local trucking company. All dynos work the same way, they load the engine down until it can't accelerate at full throttle at a specific RPM, and the torque it's developing at that speed is measured. Then a math formula is used to calculate horsepower. The speed is varied up and down, and the torque output is recorded. Then a RPM/torque graph is plotted and the HP is calculated for any specific point on the graph. There will be a high point of the graph for both HP and torque. Exceeding either point results in a reduction of output. The HP curve peaks at a noticeably higher RPM than the torque curve on most engines. I prefer to use a dyno that bolts directly to the back of the engine, rather than one that measures wheel HP. My dyno is a "water brake" type that bolts to the bellhousing and resembles a torque converter. It is filled with water to provide the load on the engine, and depending on the torque capability of the engine, sometimes a large volume of water is needed to avoid boiling the water in the load cell. So far, the highest output engine I've had on it was a MOPAR 440 pull truck engine which produced 714 HP at 6500 RPM, on one Quadrajet carburetor and gasoline. Obviously, it was highly modified!
Roller-type dynos that measure HP at the wheels are good for evaluating tuning modifications like carburetor jetting and ignition timing adjustments, but similar measurements can be done with a stopwatch and a long hill as long as the atmospheric conditions don't change dramatically. It's possible to get widely varying dyno numbers with a simple change of temperature and/or relative humidity. Our dyno runs in the race shop were always corrected for those factors to get an actual HP reading.
Confused yet?
LOL!
Jerry
