The performance of an engine installed in on-highway vehicles can be tested on a chassis dynamometer.
NOTE: Due to driveline efficiency and engine-driven accessories, the engine horsepower when measured at the rear
wheels will be reduced by approximately:
• 20 percent for single axle vehicles
• 25 percent for tandem axle vehicles
NOTE: These percentages are used for engine run-in only and are not to be used as absolute figures.
Caution: Low profile radial tires are more sensitive to heat than bias ply tires. Excessive operating time at full
load can damage tires due to overheating. Check the tire manufacturer’s recommendations for the maximum allowable chassis dynamometer operating time.
Follow the general safety precautions listed below while operating the chassis dynamometer:
• Use tires that have more than 160 kilometers [100 miles] on them. Do not use new tires.
• Do not use recapped tires or tires of different sizes or designs.
• Make sure the tires are inflated to the manufacturer’s specifications.
• Remove all rocks or other material from the tread of all tires that will be rotating on the dynamometer rollers.
• Make sure there is correct overhead clearance for exhaust stacks, air deflectors, or other attachments above the cab.
• Carefully position the vehicle on the rollers.
Caution: To prevent damage to the chassis dynamometer, there must be some slack in the tension of the tie-down chains.
•Attach the tie-down chains to the rear of the vehicle, and put wheel chocks in front of the front wheels.
• Adjust the vehicle and dynamometer room exhaust system to make sure all exhaust gases are removed from the room.
•Refer to the chassis dynamometer and vehicle manufacturer’s recommendations and specifications for testing procedures.
