As dyno-related technology becomes more standardized and the costs involved have continued to come down in turn, the idea of installing a dyno cell in one’s shop is becoming a viable prospect for a growing number of engine builders.
The key benefits are obvious – the shop can ensure each engine runs perfectly when leaving the shop, have the ability to offer services the competition can’t, and test various components to determine their performance firsthand – but it’s still a substantial investment, and the costs aren’t relegated to just the machinery itself.
“When I go into the field I see a lot of good test cells, and a lot of bad test cells,” Bret Williamson once told us during SuperFlow’s Advanced Engineering Technology Conference presentation. “And I’ve seen why these things make a big difference in the results.”
Pre-fabricated dyno cells can help take some of the guesswork out of the equation, but there are still a number of variables to consider, and some folks have requirements for their dyno cell builds that necessitate a more customized approach. Here we’ll look at some of the key components of a dyno cell construction and get some insight from industry leaders about the factors that need to be considered in order to make sure your build is safe, accurate, and efficient.
Dimensions and Location
While there are no set rules for the square footage you need to dedicate to a dyno cell, there are a few guidelines worth considering to ensure its repeatability and success.
“We would consider 12 feet by 12 feet to be the minimum footprint,” says Dru Freese of BluePrint Engines. “Room size can vary depending on what you want to do in there besides just dyno test. For example, if you plan to work on the engine in the cell and do things like swap out camshafts and manifolds, you’ll want a bigger room to work in.”
Assuming you have some options on where to put the dyno cell within your building, you’ll want to consider whether a particular spot is not only accessible and convenient for moving engine hardware in and out but also its proximity to an existing water drain and how the ventilation will be routed into and out of the room from that location within the building.
You’ll also need to factor in the operator’s console into your planning. This area will be located outside of the test cell for safety reasons, as a failure could result in parts flying out radially from the engine and injure the operator. “We recommend that the operator sit in-line with the crankshaft for maximum safety,” notes Mike Giles of SuperFlow. “We also do not recommend installing a viewing window that faces the sides of the engine, as that can be a safety risk if a projectile impacts the glass and shatters it.”
Noise is also another factor that must be taken into consideration – you need to make sure that not only can folks communicate easily from the control area and that individuals in other parts of the building aren’t disturbed, but that the system also won’t trigger sound complaints from any neighboring businesses or homes. Options for sound proof doors and windows are numerous and using multiple layers of sheetrock is a common method for suppressing sound coming through the walls and ceiling. Companies like Noise Barriers also offer pre-fabricated kits that take sound suppression into consideration as an intrinsic part of their design, but there are other elements of the dyno cell that can cause a ruckus as well.
“Each cell in our engineering department has a 38,000 CFM fan,” says Freese.
“When you move that much air, it makes a lot of noise, so we also use duct silencers in the ventilation system.” These silencers are able to attenuate wind noise simply by virtue of their internal geometry rather than using acoustic material to absorb the sound. “Don’t ask me how they work, but they do work.”
Attention to detail will make a big difference here as well. “A properly designed test cell can reduce the sound level by 40 to 50 decibels between the inside of the cell and the operator position,” notes Giles. “Most of the sound will exit the room through the door, the window, and any leaks through the walls, so add caulk all around the window panes during installation and be sure that all electrical boxes are caulked all the way around their penetration through the wall, and even caulk around any wires where they enter the conduit. Sound travels very well down long tubes.”
With the combination of high mechanical stress, heat, and flammable fluids all in the mix, a proper fire suppression system is vitally important when building a dyno cell. “When designing your test cell, pay special attention to local fire codes and insurance requirements,” says Giles. “This can include sprinkler heads installed inside the test cell, but you’ll want to use high-temperature pop-offs due to the heat generated during normal use.”
With heat, significantly component stress, and flammable liquids all regularly occupying the same space, a proper fire suppression system is a must. Here we can see one of the systems installed at BluePrint; their team fully tested the system to determine how close the flame-detection wiring had to be to the engine to quickly activate the CO2 system.
While there are no standards in terms of design, Freese offers BluePrint’s strategy. “Our fire suppression has always been CO2, three nozzles positioned above the engine, and one nozzle mounted on the wall which is aimed at the fuel pump and regulator. The system really needs to be wired in to the dyno and fuel controls as well as the ventilation fan, that way if the suppression system is triggered either by the operator or from a sensor, everything stops. It’s obvious why you need to stop the fuel flow, but the ventilation system is very important too – if you don’t shut the big ventilation fan down, it will suck half your CO2 out the vent.”
It’s also important to have an interlock between the fire suppression system and the dyno, Freese points out. “The interlock won’t let the dyno operate unless the fire suppression system is full and the lines are charged.”
A dyno cell will require water for both the absorber, also known as a water brake, as well as the engine itself. The water supply can either be an open system design, where the water is supplied from the city water supply, or a closed system, where the water is recirculated through a tank. Either design requires an easily accessed water shutoff for supply and return water in the test cell.
“Water brakes need volume and pressure – in some cases you might get by with city water, but we choose to boost it with a pump in a closed loop circulation,” says Freese. “It really just depends on how much water you use and what that water costs. Most water brakes will function best with a sump in the floor for them to drain into. Our sumps are around two feet square and two feet deep.”
Whether you decide to use the city water supply or a recirculating system, you can test the water supply capacity by placing a control valve and a pressure gauge at the end of the supply line, with the gauge positioned on the supply side of the control valve. “Typical city water systems for homes only deliver an adequate water supply for engines up to roughly 100hp,” says Giles. “Commercial areas are usually somewhat higher, but keep in mind that a water line with a diameter that’s at least 1.5 inches is required for the average 600hp engine.”
The fire suppression system really needs to be wired in to the dyno and fuel controls as well as the ventilation fan, that way if the suppression system is triggered either by the operator or from a sensor, everything stops. – Dru Freese, BluePrint Engines
“If the temperature of the air going into an engine rises and falls during a test, or if any exhaust gas recirculates within the room, the test results will vary in an unpredictable manner,” says Giles. “It seems obvious, you have to remember that air is a critical property of the combustion process, and without an adequate supply of clean air it is difficult to reliably create power.”
“Inadequate ventilation is a common issue,” Freese reiterates. “Years ago when we built our first cell it seemed like it had enough ventilation – until we tried to run an endurance engine for an hour. Then it became obvious that we needed more. I think we ended up close to 20,000 CFM to get it to work right.”
Both the airflow quantity as well as direction are important factors when your goal is repeatable test results. “Air should enter at the front of the cell and flow across the engine to the rear of the cell,” says Giles. “And the room fans should be positioned so that the air is extracted from the room, even if the operator door is open. Fans should also be placed at the end of the exhaust duct so contaminated air won’t be pushed through leaks or auxiliary ducts into other parts of the building.”
Of course we’re just scratching the surface of dyno cell design and implementation here, but hopefully these foundational tips will help get the gears turning if you’re thinking about adding one to your bag of tricks. Got some questions about adding a dynamometer to your shop? Give the experts at SuperFlow a buzz to find out what’s what.