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Dynamometers and Dyno Operating Systems
Some would say that a dynamometer is no longer a luxury for engine builders today. A dyno has become an absolute necessity - not just for performance engine builders and racers, but for all types of engine builders.
By Larry Carley
The data collected while an engine is running on a dyno can be analyzed to maximize the power gains from various modifications (changes in the fuel mixture, ignition timing, valve timing, compression, the induction system, exhaust system, etc.). Performance engine builders use dynos to measure horsepower and torque so they can optimize engine performance. By baselining engine performance, any improvements that result from additional changes can be precisely measured and documented.
Performance engine builders also use engine dynos to simulate the effects racing conditions can have on their engines; to verify the durability of valvetrain components, the engine's bottom end, lubrication, ignition and fuel delivery systems; and to document their work. Big torque and horsepower numbers don't mean a thing if the engine can't finish a race.
A dyno can also be used to control the initial break-in of the engine after assembly (rings, camshaft, etc.). Making sure the engine has normal oil pressure, intake vacuum, no leaks, no unusual noises in the valvetrain or bottom end, and is running properly before it goes out the door can greatly reduce the risk of warranty problems later. This is especially important with high-dollar rebuilds and hard-working gasoline and diesel engines that end up in fleets or trucks.
A dyno can also be used to make normal tuning adjustments such as ignition timing, fuel mixture, valve lash, etc. on everyday engines to reduce the risk of "installer error" screwing things up. Checking exhaust temperatures or using a wide band oxygen sensor to monitor the air/fuel mixture in each cylinder can reveal problems that might cause an engine to go into detonation or preignition. Monitoring coolant temperature can catch any problems that might restrict coolant flow (like a faulty thermostat).
A dyno can also be used to diagnose performance problems. In many instances it's almost impossible to accurately diagnose a fuel, ignition or cooling problem unless the engine is running under load. This can be done with the engine out of the vehicle on an engine dyno, or with the engine in the vehicle on a chassis dyno.
Vehicle manufacturers use both engine dynos and chassis dynos to validate new engine designs, to develop the ignition and fuel maps for their engine control modules, for durability testing and to verify emissions compliance. The OEMs typically use expensive high-end dynos with all kinds of data acquisition inputs and automated test programs. This level of sophistication is more than most engine builders need for their customers. Even so, many NASCAR and other high dollar racing teams use dynos with capabilities that are on par with the dynos the OEMs use.
If money were no object, every engine builder would probably have his own dyno - if for no other reason than to verify and control his work. A dyno can certainly give one bragging rights if an engine produces a lot of power. But more importantly it can validate that the machine work and parts that went into the engine are doing what they are supposed to be doing. The dyno readings will show whether or not the engine is delivering the desired torque and horsepower throughout its rpm range. Additional data that can be collected during a dyno run can also be analyzed to reveal what's going on with airflow, the air/fuel mixture, fuel consumption, emissions, cylinder temperatures, oil and coolant temperatures - heck, you name it.
Building a performance engine today without a dyno is like driving at night without a road map. You know where you want to end up but may not be sure of the best route to your final destination. And since real men never ask for directions, you may make a lot of wrong turns along the way - leaving you unsure where you are at any given moment. So it is with performance engine building. Years of experience may have taught you that certain combinations of parts can produce certain levels of horsepower. But how much horsepower, exactly? And could the engine make more power or have a better torque curve if you tried something different? There's no way to know without a dyno.
Many engine builders use their dynos to market their capabilities as well as their credibility. Phrases such as "Dyno Tested" or "Dyno Proven" have genuine impact and can sway potential customers to bring you their business. The torque and horsepower numbers generated by dyno testing are real numbers, not just numbers pulled out of thin air. Of course, dyno numbers can always be exaggerated or fudged to make them seem more impressive than they really are. That's why reputable engine builders should always use "corrected" torque and horsepower values that accurately reflect the engine's true power output.
To get really accurate dyno numbers, tests need to be done under carefully controlled conditions. If you're conservative, you'll do a series of three to five runs and then average the numbers to get relatively accurate torque and horsepower figures. But if you just want the biggest numbers, you'll do a series of runs and pick the one that generates the best results and toss the rest.
Engine power can vary a great deal depending on ambient temperature, barometric pressure and relative humidity. Cold air is denser than warm air, so cold air makes better power numbers. Air is more dense at sea level than in Denver (which is a mile above sea level). Because of this, the dyno numbers for an engine tested in Miami might be 15 to 20 percent higher than if it were dyno tested in Denver. High humidity also allows more spark advance than dry air. So testing on a cool damp day may result in more power than on a hot, dry day. Most dyno software programs allow the raw "uncorrected" numbers to be readjusted using standard correction factors. The "corrected" numbers are the ones that really allow you to compare one engine to another regardless of who built the engine or where it was dyno tested.
A dyno does not measure horsepower directly, but calculates horsepower by measuring torque and engine speed. The math is fairly simple: torque times engine rpm divided by 5252 equals horsepower. The dyno uses a water brake, eddy current brake or AC (alternating current) brake to create resistance while a sensor measures how much torque in pounds-feet (lbs. ft.) the engine produces. Most of the dynos designed for aftermarket engine builders have water brakes. Water brakes typically have a broad dynamic range and can handle engines from 20 to 1,500 horsepower. One dyno supplier we interviewed said some customers are using their water brake dyno to test engines up to 2,500 horsepower even though their dyno isn't officially rated to handle that much power.
Eddy current brakes use a rotating metallic disk in a strong magnetic field to create resistance. Eddy current dynos are more expensive and typically have a much narrower power range (say several hundred horsepower) but they are also more precise. Because of this, eddy current dynos are used more for research and development work. Alternating current dynos, by comparison, typically cost three times as much as an eddy current brake. They also use a magnetic field to create resistance, but can also drive the engine as well as absorb power to simulate inertia loading on the engine during deceleration. This allows AC dynos to simulate actual racing conditions, but the costs are high: from a couple hundred thousand dollars for an entry level system to several million for a high end system.
The design of a dyno can also affect its accuracy and repeatability. The water flow control valves on water brake dynos, how the valves are regulated, the accuracy and calibration of the torque sensor, and how the software processes the data all affect the numbers generated on the dyno. Consequently, the same engine tested under similar circumstances on different days or on different dynos may generate somewhat different numbers. There should not be a lot of variation, but some variation is to be expected, especially when different dynos are used to test the same engine. That's why two different engine builders who assemble the same engine with the same parts may get slightly different dyno results.
The software that collects, analyzes and displays dyno data may be DOS or Windows-based. DOS is mostly history these days, but may still be found on some older equipment. Windows-based software obviously takes full advantage of the latest technology, and provides the best graphics and features. The control software typically gives the user a great deal of flexibility in how the screens can be set up and arranged, what kind of data is collected, and how the information is tabulated and displayed.
Software inputs include parameters such as ambient temperature, barometric pressure and humidity for test consistency, and engine monitors for oil and coolant temperature (again for consistent test results), exhaust temperatures, airflow, exhaust oxygen (if using wideband O2 sensors to monitor air/fuel mixtures), throttle position, engine rpm, manifold vacuum/pressure, even crankcase blowby (with the proper airflow sensors). In short, you can monitor just about any kind of data you have the ability to measure and record.
Most engine builders don't need a lot of data acquisition beyond the basics, and adding additional hardware can be expensive. But for durability testing or development work, the more things you can measure and quantify, the better.
What's important here is to be consistent. Variations in ambient temperatures, even oil or coolant temperatures can cause variations of up to 10 percent or more in an engine's power output. If these factors are not taken into consideration, the dyno results will be inconsistent and you may not know why. That's why automated dyno testing that reduces the human factor as much as possible has become more common. The results are more consistent and repeatable.
Nevertheless, many operators still like to play with a manual throttle control when doing a dyno run. It's more up close and personal than pressing a button, sitting back and watching the computer run the test. On the other hand, an automated dyno test that starts with the engine at a specified rpm and then accelerates the engine at a precise rate to maximum rpm may give more consistent results. What's more, an automated program can have safety limits programmed into it to stop the test if anything goes wrong. It may not wait for metal fragments to ricochet off the dyno walls before it pulls the plug on the test.
Automatic "step" tests that hold the engine at a certain rpm for a certain period of time and then advance to the next rpm are often used for mapping fuel mixture and ignition curves at various speeds. This capability is important for performance tuning as well as PCM programming.
Durability testing requires automated dyno controls, unless you have an operator who can maintain his concentration for hours on end without taking breaks or sleeping. The vehicle manufacturers typically run durability tests that last up to hundreds of hours at a stretch, with the dyno running 24/7 until the test is complete. Most engine builders don't need to do this kind of testing unless they are trying to get an OEM rebuild program validated, and even then the OEM may do the testing for them. But some NASCAR teams are running test engines for up to 500 miles to see how certain parts hold up. Some off-shore power boat engine builders are doing the same thing because an engine can't win a race if it doesn't finish the race.
Shopping For A Dyno
If you are thinking about buying a dyno, the first thing you have to decide is what you are going to use the dyno for. If you are only going to do engine break-in, basic tuning and power testing, an entry level dyno with basic instrumentation is all you need. An entry level water brake dyno these days typically costs $12,000 to $20,000 depending on the features and controls.
If you're going to use a dyno on a daily basis for serious engine testing and development work, you'll need a dyno designed for a performance engine builder. These typically start in the $35,000 to $40,000 range and go up from there.
If you are a NASCAR engine builder and want to do durability testing and racing simulations, you'll probably need a high end dyno with an alternating current brake. The cost here can run from $200,000 up to several million!
Like any other piece of equipment, you need to justify the cost before making the investment. Buying a dyno to improve a racing program is a different kind of purchase than buying a dyno to sell performance engines to the public or to control break-in to reduce warranty claims. One way or another the machine has to pay for itself otherwise it is just a high-priced toy. The payback can come a variety of ways: from getting more customers, from having better satisfied customers (thus more loyal customers and better word-of-mouth advertising), fewer comebacks and warranty problems, and the added profitability of charging additional fees for dyno testing. The dyno's greatest payback, however, often comes from what it does for you and your knowledge. The more you know about the engines you build, the more power you can get out of them.
Some shops charge a flat fee for dyno testing (so much per hour or per day) while others build a cost factor into the cost of the engine itself. Either way, the customer pays for the time an engine spends on the dyno.
The cost of the dyno itself is only part of the investment that's usually required for dyno testing. Unless you plan on testing engines outdoors, you will also need a dyno room or "cell" to house the dyno. The room provides a controlled environment for testing, and also helps keep noise, exhaust fumes and flying parts out of the rest of the shop. You can build your own dyno cell, or you can custom order a prefabricated dyno cell from a company who specializes in this type of product. Prefab dyno cells can run from $10,000 up to $30,000 or more depending on their features. You can assemble the cell yourself or have it installed. Plans can usually be drawn up within a week, and delivery may take 2 to 6 weeks.
Important things to consider when building or buying a dyno cell include noise control, ventilation, safety and local zoning regulations. A big block Chevy running at full throttle with open headers makes a lot of decibels. Most urban areas have noise control regulations, and many have lower noise limits for evening hours. Consequently, you need a dyno cell that can provide adequate noise suppression (typically 40 decibels or better) without affecting exhaust backpressure, engine breathing or engine performance.
An engine sucks a lot of air when it is running, and it also needs additional airflow around it for cooling. If a dyno cell doesn't have enough airflow, engines can overheat and hot air can reduce the torque and horsepower readings. Some guidelines say the dyno cell should have 10 to 15 times the airflow in cfm (cubic feet per minute) of the largest engine that would ever be tested in the cell.
A dyno cell should be large enough to provide adequate work space all around the engine for making connections and adjustments, good lighting, a large door to allow engines to be easily moved in and out of the room, and a Lexan or wire-reinforced tempered glass window so the dyno operator can watch for trouble during a test. Regulations may also require sprinklers or a fire suppression system. The room should be designed so you can easily clean up any oil, coolant or fuel spills, and the walls and ceiling should be fireproof - and hopefully capable of containing flying engine parts.
Chassis Dynos & Road Simulators
Chassis dynos and road test simulators have long been used for emissions and driveability testing. Many performance shops also use a chassis dyno for performance tuning. There's a hot market these days for shops that can reprogram PCMs to accommodate bolt-on performance goodies such as hotter camshafts, bigger turbochargers and aftermarket intake and exhaust systems.
The nice thing about a chassis dyno is that you can test the engine while it is still in the vehicle. You can also see how much horsepower actually reaches the drive wheels (friction in the drivetrain and slippage in the torque converter can reduce power by 5 to 15 percent or more).
Chassis dynos have large rollers (single or double) that go under the vehicle's drive wheels. This requires ramps for an above-ground installation, or cutting a recess into the floor to accommodate the rollers.
A chassis dyno is usually located in a dedicated stall or service bay so it doesn't interfere with other work in the shop. Other items that are necessary include exhaust hoses and venting, and a large fan to provide adequate airflow while the vehicle is running on the dyno. There is also more liability involved with a chassis dyno because the vehicle has to be strapped down to keep it from jumping off the rollers. And if something goes wrong during the dyno run, the customer may hold you responsible for any damage that occurs to their vehicle (whether or not they signed a waiver - which is always recommended).
In summary, dynos are valuable tools engine builders can use for a variety of purposes. Compare the features and prices of various dynos before you buy, and ask other engine builders who have dynos what they like (or dislike) about their equipment.
Most dyno suppliers provide training and technical support for their products, and the learning curve to getting started is fairly quick. The software on most dynos is easy to use and user-friendly, and you don't have to be a computer programmer to set up or operate the controls. You just need a willingness to make the plunge into dyno tuning and testing.