One of the only ways you can prove your worth as a race engine builder – besides on the racetrack, of course – is on a dynamometer. Being a shop without a dyno may be akin to running blindfolded: you can surely build a good engine, even a winning engine, but you probably won’t know why or it’ll take you much longer to learn from the experience you have gained.

A dyno takes what is the black art and science that you do in terms of engine building and turns it into a tangible asset that you can sell to your customers. If you are a very small shop that just assembles motors to a “recipe”  or some proven combination, you may think a dyno is just a luxury, but even then you may still need one to get the most out of your builds and move to the next level.

If you can’t afford a dyno yet, then you might make a deal with a shop who has one and rent it. If you just want to build engines and break them in, then a run-test stand may be the best solution and is more economical. Either choice will save you some headaches in dealing with customers who don’t set up your motors correctly.

But to gain any type of advantage in performance, you need a tool that will measure and trace your results. You need a tool that is repeatable and easy to use. Fortunately, there are a number of products on the market that will fit the bill.

There are several kinds of dynamometers on the market but the two most common in the performance industry are water-brake and eddy current. Both types have advantages and disadvantages, say our experts, but what you choose ultimately boils down to what you need to produce the best results for the types of engines you build.

Water-Brake

Water brake dynos have been manufactured for many years and are relatively common in the performance industry. Depending on the size of the absorber, they can easily handle high horsepower and typically are less expensive compared to other, quicker-reacting absorber types.

Their drawbacks are that they can take a long time to stabilize their load, and they require a constant supply of water to the water-brake housing for cooling. And depending on where your shop is located, you may not be able to tap into a municipal water supply and drainage could also be an issue.

To get around this, many shops install large water tanks and use pumps to supply the proper flow of water and prevent contaminated water from returning to the environment. Water is added until the engine is held at a steady rpm against the load, with the water then kept at that level and replaced by constant draining and refilling, which is needed to carry away the heat created by absorbing the horsepower.

The housing attempts to rotate in response to the torque produced, but is restrained by the scale or torque metering cell that measures the torque.

Chris Wright, from Pro Car (a dyno shop and engine building/tuning operation in Akron, OH) says his dyno is one of only two like it that exist. Wright says he has created a hybrid (like many shops have done to fit their needs) – the water-brake has been completely modified to handle directly coupled whereas most dynos have a gear reduction, says Wright.

“It’s a modified Clayton, and directly coupled it’ll handle over 10,000 rpms and 2,500 horsepower steady state,“ he explains.

Eddy Current

Eddy current (EC) dynamometers are the most common absorbers used in modern chassis dynos. The EC absorbers provide a quick load change rate for rapid load settling. Most are air cooled, but some are designed to require external water cooling systems.

Eddy current dynos require an electrically conductive core, shaft, or disc moving across a magnetic field to produce resistance to movement. Eddy current dynos are more expensive and typically have a much narrower power range but they are also more precise.

Wright says he bought a double retarder eddy current chassis dyno because he wanted something that could handle high horsepower and diesels as well. He says his chassis dyno will handle up to 2,500 hp and 9,000 ft.lbs of torque. The chassis dyno is mostly used for his street performance customers to do drivability and performance tuning and Pro Car even holds a charity event called “The Ground Pounder” to allow guys to run on the chassis dyno for bragging rights.

“It’s easy for customers to come in and have work done on the chassis dyno because they can just drive up on it,” Wright explains. “When I bought the unit it cost $70,000 – new ones now are about $90,000. Most people can’t believe it cost that much because it’s so small, but it’ll do everything. I priced some other similar dynos but couldn’t get close to doing what we can for the price.”

Correction Factors

Depending on which correction factor you use, you could have a significant swing in recorded engine output whether you are using the raw number, SAE number or the outdated Standard Temperature and Pressure (STP) number, say experts. Therefore, besides setting up your dyno and cell correctly, you’ll have to also be sure to plug in the right correction factors.

The current SAE standard for correction is SAE J1349, which is used by all the OEMs and major engine development labs. Power is corrected to reference conditions of 29.23 inches Hg (Mercury) of dry air at 77 degrees F. This standard requires a correction for friction torque, which can be measured on the dyno or estimated.

When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine running speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration and assume an ME of 100%.

The STP standard is another power correction standard determined by the SAE and has been widely used in the performance industry for years. Power is corrected to reference conditions of 29.92 inches Hg of dry air at 60 degrees F. Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4% higher than the SAE power numbers.

Data Acquisition and Testing

In many cases it’s 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.

All of the major car manufactures use both engine dynos and chassis dynos to validate their 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 the biggest, most expensive dynamometers money can buy, and they will collect data from every possible sensor input available and run on multiple channel data acquisition systems.

This level of sophistication is probably more than you will need for your racing and performance customers unless you are servicing very high-end racing teams. The data acquisition and control package you use doesn’t have to be from the same company as the actual dyno, but doing so does help reduce headaches and compatibility issues.

Dyno Cell

Engine Masters participant Greg Finican says he recently bought a used DTS dyno from Arizona after he talked to someone at the manufacturer who told him he knew the history of it and who had bought and sold it. “It’s such a small industry in some ways when you can talk to someone about a piece of equipment and they know the whole history. I was told that it was not used very much and had low mileage, so I bought it.”

Finican says there’s a lot more that goes into setting up a dyno and a test cell than meets the eye. He says he’s had the dyno for over six months and it’s still not fully not up and running yet. “The dyno right now is just sitting here waiting to be upgraded with the new software,”  he says. “I’ve not really done a legitimate dyno pull yet. We’ve been able to run it a little just to make sure the cooling system works, but I’m still waiting for some of the final pieces to come.”

One thing that Finican had already was the perfect space for the dyno in one of his buildings. “We made some renovations to make it into a proper dyno cell,” he explains. “The dyno itself cost about $21,000 and required about $2,800 in replacement parts, which was okay to get everything up and running. That’s pretty good in my opinion.”

But he found that, even having free space for the dyno, to do it right, it’s more expensive than the dyno. “You have to have the exhaust system in there, the water supply system, the fire suppression that you need and the control room. To have a real dyno room it will cost more – and I already had the space.”

Go Power’s Azor Phelps agrees that you’re likely to spend more money on the cell than you are on the dynamometer equipment itself. “You have to manage fuel, air, water, sound and protection in case something blows up. And there are levels of protection on top of that. You can skew your results if you don’t have your room set up properly,” he says.  

“The two biggest potential drawbacks are you don’t move enough air and you starve the engine. The next biggest challenge is you don’t have enough water to the dyno. And without enough water you can’t hold the load or the load is inconsistent. If the water supply is inconsistent then your test results will be, too,” Phelps says.

“We strongly recommend that customers use a water tank and a supply pump because it’s very difficult to run a high horsepower engine on city-supplied water, even if a guy has a big tank and it’s going from 100 feet in the air,” says Phelps.  “A customer tried it once but it didn’t work, so he had to use a boost pump and a regulator to get the flow they needed.”

Pro Car’s Wright says his shop had to get a mayor’s variance to use city water, because they couldn’t get enough water to run it. They use a four-inch water line that comes in directly off the street.

“It took special consideration to get hooked up but we were able to tie into a main line with the fire department just down the street. Most people don’t have a water supply that is sustained like we have that can handle as much power as we can. A lot of dynos with little water-brakes are fine for doing a pull but they will cavitate quicker and boil the water, which then turns to steam. Once that happens you lose control.”

Pro Car’s dyno has a lot of custom fabricated parts such as an integrated starter and alternator. And everything in the room was made out of stainless steel, says Wright, so it will last basically forever.

Wright agrees on the time and money needed to get the room set up the way the team wanted. “The dyno room has been here a long time and has changed over the years. My dad had an old Eaton dyno years ago but we  needed to upgrade. The dyno room itself cost about $600,000 to do over about 4 years.”

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 dynamometer 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.