Issues regarding the use of dynamometers

A dynamometer is basically a tool to deliver an effective comparison or analysis of an engine output or performance. Dynamometers are a lagging indicator, which means the dyno only tells you what has occurred during the dyno run or test period. After you have applied your best engine building skills, the dyno serves the purpose of evaluating the engine's capabilities at a specified moment in time. A dynamometer mainly measures Horse Power (usually at the crank shaft but in the case of a chassis dyno, Horse Power is only measured at the rear axle), torque, RPM range over which the engine was tested, temperature and air flow (volume and velocity of the air that ventilates the engine). Some dynamometers also measure noise levels of exhaust and intake manifold pressure, fuel flow, BSFC (the measured fuel flow in pounds per hour divided by the horsepower), and pressures such as oil pressure when appropriate. Top racers own a dyno, as it is a very powerful tool. It provides valuable information about the performance of engines, transposed in a set of graphs. As dynamometers measure engine output, isolate and quantify the metrics of horse power and torque, they are very useful for elaborate performance tests. In preparation for performing a dyno test there are certain metrics that you should have or should obtain prior to planning the test. These include the minimum horsepower, the gear ratio if you are not attaching the water break to the output shaft of the motor. A good dyno allows the user to enter today's environmental or altitude conditions. When reporting, the software provides the correction factors so that each day is measured as though it were the same as the last time that the engine was tested or to a set baseline so that you always achieve a set comparison. Dynamometers are very handy and useful, but they are a very expensive piece of equipment. Many of them are also extremely noisy, even when they are running on small motors. The exhaust is caustic and therefore, dynos should be used only in properly ventilated areas. Before investing in a dynamometer, certain aspects should be considered, such as the size of the working space, the possibility of storing volatile fuels, or the access to certain utilities such as proper water supply for the water brakes. A computer and a color printer are also necessary for recording and monitoring the way the engine performs. When the requirements are met, all it takes is ambition, dedication and investing the right amount of time for making refinements and adjustments.

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Improve your car’s performance by using dynamometers

The dynamometer is a device used to measure mechanical force, power and torque produced by an engine. Its inventor, Charles Babbage, is also known as the “Father of Computing. There are basically two types of dynamometers: the first one is bolted directly to an engine, and it’s called engine dyno, while the second type of dynamometer can measure power and torque without removing the engine from the frame of the vehicle, and it’s known as a chassis dyno. An engine dynamometer measures power and torque directly from the engine's crankshaft (or flywheel), when the engine is removed from the vehicle. These dynos don’t take in consideration power losses in the drive train, such as the gearbox, transmission or differential. A chassis dynamometer measures power from the engine directly through the wheels. The vehicle is parked on rollers and the output is measured. These dynos can be fixed or portable. The dynamometer works by applying various loads on the engine and by measuring the engine's ability to move the load. It is connected to a computer which uses mathematics to calculate the output of the engine. The engine is run from idle to its maximum RPM and the output is measured and interpreted on a graphic. Nearly all aspects of engine operation can be measured during a dyno run. Generally, dynamometers are useful in the development and refinement of modern day engine technology. The concept is to use a dyno to measure and compare power transfer at different points on a vehicle, thus allowing the engine or drive train to be altered, in order to get a more efficient power transfer. For example, if an engine dynamo shows that a particular engine achieves 400 N·m (300 lbf·ft) of torque, and a chassis dynamo shows only 350 N·m (260 lbf·ft), it means that in order to recover the power loss, the drive train should be inspected and improved for maximum efficiency. Dynamometers are typically expensive pieces of equipment, reserved for certain fields that rely on them for a particular purpose. They are very handy, as they can diagnose the entire way a car is functioning, but they are sometimes unaffordable.

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Examining the dynamometer data

After you have performed your desired dynamometer tests, you need to take a look at the information you received. If you have a manual recording system you should calculate and transform the torque and rpm readings into horsepower numbers. If you've got a manual electronic data collection the next step will be to print out the data.

On personal computer equipped dynamometers you should name the new data file and enter all the relevant data about the test run you have ended.

There are software packages for your dynamometers that grant you the possibility of entering virtually any parameter you want in certain windows. This is very handy, as you can store important information in a structured data base, making it more accessible. If you don’t own a system equipped with sensors that capture the weather conditions you should write them down as soon as you finish the dynamometer tests.

It is very important to choose an appropriate output report format for reviewing the dynamometer’s data. When you examine the data received from you dyno, you should discard any information gathered during periods of rapid rpm change. You should instead concentrate on the ranges where the engine maintains a stable number of rotations for at least a few consecutive seconds.

Another important step is to average the data received from the dynamometer. Even numbers with some inertial errors can still produce valuable information after they have been averaged.

If you observe any unusual numbers in your results, you have probably made some mistakes when you chose the tachometer pulse settings. Or, if horsepower is a lot smaller than you expected it to be, you should check if the throttle was wide open during the test. You should also remember about the problem of exhaust being reabsorbed into the intake system. Perform another pull, following the same procedures as the first dynamometer test, making sure you everything is checked and working properly. Remember to warm up the engine before you begin the test. On the second run, you shouldn’t make any significant parameter changes, and concentrate on repeatability instead. In fact, you are really testing the repeatability of your actions and the stability of your engine, since the dynamometer did not change between runs.

Whenever possible, when chasing small improvements, you should retest the engine in its baseline state. This additional real-time check will spare you a great deal of time in the more important and longer runs.

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