MANIFOLD-HOUSING 2278851 - Caterpillar

3406 Truck EnginesThe drivability of a truck engine depends on both the power that an engine delivers to the wheels, and how responsive the engine is to throttle movement. The most powerful engine will not be drivable if it is not responsive during normal driving conditions. As of this time, a satisfactory response test has not been developed for a chassis dynamometer.
Caterpillar's definition of engine response is the length of time required to go from a no load (idle) condition, at some engine speed, to eighty five percent of the available power at that given speed in a laboratory environment. On engine dynamometers, this is done by measuring the actual torque that the engine delivers during a full throttle constant speed acceleration. In a vehicle, it is not possible to measure power or torque accept on a chassis dynamometer and the chassis dynamometer is not responsive enough to hold a constant speed during an acceleration. The response test is extremely sensitive to variations in engine speed, so it is imperative that the engine speed be kept as constant as possible during the testing.
A test method has been developed to test dynamic response in a vehicle so that different vehicles can be compared or so that repairs on a vehicle can be evaluated. This test method can also be used in conjunction with the PAR dynamometer test to come up with a more complete picture of the overall performance of an engine in a chassis.
Since this response test is not run on a chassis dynamometer, a method of measuring engine output needs to be established. A good relative power measurement on a turbocharged engine is turbocharger boost. Turbocharger boost can be measured with a boost test kit or any other gage that is responsive and has a full range of 175 kPa (25 psi). Gages with larger ranges will not have the sensitivity required to run the test.
Due to the sensitivity of the response test to engine speed, it is necessary to have some weight attached to the vehicle. A tractor without a weighted trailer attached will usually not provide an acceptable answer because the tractor will accelerate several miles per hour during the test. This will not give an acceptably consistent results.
This response test should be run on a level road where the vehicle can be operated safely at 1100 rpm in the highest gear. Once you are familiar with this test, it can be completed in about ten miles of driving.
After the truck has been equipped with the boost gage and a test trailer, it should be driven for a length of time prior to starting the test. This will ensure that the engine is up to operating temperature. After the engine is up to operating temperature, the data collection can start. For the best results, data should be taken at four engine speeds (1100, 1200, 1300, and 1400 rpm). This will allow you to develop a response trend when the results are plotted on graph paper.