similar in operation to a fifth wheel but doesn't use accelerometers that can be influ­enced by the vehicle's body tilt. Using the vehicle's speed, acceleration, and weight (mass) and the application of simple physics equations, the exact horsepower and torque can be calculated. The horsepower and torque measured by West Automotive Performance Engineering's dyno is actually the horsepower made-good, or the horsepower left over to accelerate the vehicle after all the aerodynamic and rolling-friction losses have been overcome. These losses were accounted for and included West Automotive Performance Engineering's dyno so that a comparison with a chassis dynamometer can be made. The Mustang dyno includes the aerodynamic load that it places on the drive­train as part of its reported rear-wheel horsepower and torque. Stated another way, the Mustang dyno does not measure the horsepower made-good.

Graphs 7 and 10 show the horsepower and torque versus rpm in Second and Third gear, respectively, for the Dynojet dyno, the Mustang dyno, and from road testing with the dyno from West Automotive Performance Engineering. You can see that the horsepower and the torque, as meas­ured on the road, are closer to the Mustang dyno measurements. Also from the acceler­ation tests you can see how the Mustang dyno loads the vehicle very closely to how it will be actually loaded on the road. Based on our test data, the Mustang dyno loaded our test vehicle and measured the rear­wheel horsepower closer to what the vehi­cle experiences on the road.

Conclusions

The Test Results table summarizes the testing that we performed. Keep in mind that the peak numbers are influenced by the amount of smoothing or averaging done to the final data. For comparing dyno plots to determine losses or gains, don't focus on the peak val­ues but take a visual average by comparing the before and after curves on the same graph. If you can't see a marked improvement

on the dyno, you probably won't see a performance improvement on the street. Also, realize that both the Dynojet and Mustang chassis dynamometers are useful tools that have excellent repeatability. Both dynos measure the correct horsepower and torque for the load that they apply. Both dynos will show losses or gains from modifications. It is recommended that you pick a dyno for your baseline testing and stick with that dyno type and dyno location (and dyno operator) for subsequent testing. Always start at the same engine coolant temperatures before each run. Also, use an OBD-II diagnostic scanner like AutoTap (from B&B Electronics) to monitor your engine's operating parameters. This will provide the best indication of power improve­ments or losses. We like to monitor the engine-coolant temperature, timing advance, knock retard, pre-cat O2 voltage, and rpm. Monitoring the engine-coolant temperature lets you make sure your engine is at the same temperature before each run to produce the most consistent results. The timing advance and knock retard indicate if any detonation is occurring that results in reduced timing and lower horsepower. After doing some research, the pre-cat O2 voltage can provide a correlation to the air/fuel ratio even though the O2 sensors are not too reliable in this air/fuel ratio region.

The bottom line: dyno numbers are for show, and track times are for the dough! CHP