A friend of mine is part of a Ford Focus club and he made arrangements at a local speed shop to have the member's cars tested on their dyno. He asked me if I wanted to run my Impala. How could I pass up this chance?
Here is a little background for those of you who are too familar with the performance aspect of cars. Horsepower (or HP) is a standard of power measurement. When auto manufacturers say their engine is rated at a certain HP, unless otherwise specified, this is the HP you would get at the flywheel of the engine. However this is not the same HP as you would see at the drive wheels.
In addition to moving the car, the engine also has to drive the alternator, A/C compressor, power steering pump and other accessores. Power is transferred to the wheels through the transmission and this also consumes HP. A rule of thumb is 80% of an engine's rated HP is what you would see at the drive wheels.
So to get a measurement of how much HP you get at the drive wheels, you have to run the car under a load. This is where the dynamometer (or dyno) comes in. The dyno consists of a big drum that the car's drive wheels sit on. This drum is connected to a computer and it senses how fast the drums are rotating. The computer is also connected to your car's number one plug wire so it knows the engine RPM. The car is tied down so it won't slip, the car is put into gear and run up to a set RPM (revolutions per minute).
This is a photo of a dyno that is similar to the one that I had the Impala on. You drive the car onto the rack and it lifts it up to the hight of the drums. Then you drive onto the drums and lock the car down.
The computer takes all the numbers and calculates the horsepower and torque ratings, correcting for ambient temperature and air pressure. Here is a photo of my car on the dyno.
These are the results from the two runs.
The average maximum HP from the two run was 158 HP and the torque was 179. This is approximately 80% of the rated HP and torque from Chevy (200HP 225 lb-ft) for the 3800 Series II engine.