Superflow SF-1 Static Dynamometer Test Cell

Static Dyno vs. Rolling Road

Rolling roads are good for on-the-spot comparisons between products, and are an excellent tool for the back to back testing of simple tuning items such as intake and exhaust systems, but should you need to power down the engine to make big changes like cylinder heads or turbochargers, maintaining parity between runs can be difficult. This problem is compounded as power is lost through the transmission and so this factor needs to be calculated into your displayed horsepower to give you a real flywheel power estimation.

Rolling roads also allow your engine to get extremely hot, often only one really good power run can be made per hour and should you want to perform any kind of high stress endurance testing you will need a very substantial cooling system to avoid expensive engine rebuild costs.

As for the output from a rolling road, estimated engine flywheel power is not a problem if you know an exact transmission loss percentage. However generally these losses can only be theorised and are not known with 100% accuracy. For this reason we use a Superflow SF-1 Static Dynamometer system, fitted in to our own test cell to give us accurate and repeatable flywheel power measurements in a temperature controlled environment.

If you want to know your engines real torque and horsepower output, a static engine dynamometer is the only way to be sure, and with repeatable power runs accurate to within 2 BHP, the figure you get is exactly what your engine has at its flywheel, with no calculations or correction factors involved.

Our Test Cell

The test cell is a sound insulated chamber on site at Abbott Racing UK. We decided to build our own dynamometer on site while we were working on our race development program in 1996. At the time we were racing against 1.8 Honda Integra Type-Rs which left the Honda factory blessed with over 190 BHP in simple road trim! The SAAB 2.0 normally aspirated unit we had to work with leaves SAAB with a not so impressive 130 BHP. Not exactly level grounds for a race series.

In order to provide a real challenge for the Hondas with their V-TEC variable valve timing systems, we needed a test bed within easy reach so we could develop the SAAB engine as quickly as possible. During the development process our ideas in many cases went from conception to test cell in less than 24 hours - this degree of flexibility and speed of development would never have been possible without our own Dynamometer within easy reach.

Now the race program is completed our test cell is used for road tuning development work, with the same spontaneous "concept-to-test-bed" mentality our upgrades such as big intake pipes and ECU upgrades can be developed in a matter of days rather than weeks.

The explanation below is only intended as a loose guide to the Dynamometer operation and therefore some of the descriptions and conventions used have been simplified to make the information easier to read and digest.

Overview of the SF-1 Dynamometer system

The SF-1 System comprises the following subsystems: engine stand, power absorber, cooling tower, instrumentation. In addition to these subsystems we have developed our own oil-water cooling jacket to maintain oil temperature and an air-water intercooler bath to regulate the intake temperature. To further aid the Dynamometer operator, a full set of conventional instruments have been fitted to the cell to monitor the engine being tested.

Engine Stand - The SF-1's engine stand is powder coated and sturdily constructed in steel and mounted on four heavy duty castors. The cooling tower and absorber systems are also mounted onto the engine stand, this forms the basic core component of the SF-1 system.

Power Absorber - The SF-801 absorber unit mounted on the engine stand is capable of measuring up to 1000 lb/ft of torque up to 6,000 RPM, and 600 lb/ft at its peak of 10,000 RPM. It is in the absorber that pressurized water resists against the engines torque. The absorber unit requires 10 gallons of water per minute for each 100 HP the engine delivers. This volume of water has to be delivered at a minimum pressure of 35 Psi.

To achieve this requirement, a 1000 gallon (4550 litres) reservoir supplies a 3 HP pump which is fed directly to the absorber unit. Water expelled from the absorber is held in a reserve tank and then fed back into the main 1000 gallon reservoir by a level controlled secondary pump, which is activated only when the reserve tank is 75% full. The Power Absorber houses the load-cell that measures the engine torque. This torque can be converted into Horsepower using the engines RPM which is also monitored on the load cell.

Cooling Tower - The cooling tower is a heat exchanger that takes the place of the car radiator. It is fitted with a thermostat that allows the engine cooling water to be set and maintained at any temperature between 65 and 82 degrees Celsius. Coolant from the engine is pumped through a coil inside the cooling tower where its heat is exchanged with the fresh cold water that surrounds the coil, this water is fed in by the pumps from the main reservoir on startup, and then sealed once the tower is full. The tower maintains the temperature set on its thermostatic valve, letting in cold water only when the tower temperature begins to rise above the desired level. This ensures the coolant remains around 2-3 degrees within its setting.

Instrumentation Systems - The Absorber is controlled by two instrumentation systems, the SF-730 data control/acquisition unit and the SF-1809 Stepper control supply. The SF-1809 is responsible for the direct control of the stepper valve on the Power Absorber, this limits the amount of water in the absorber unit and therefore controls the resistance against the engines torque. The SF-730 controls the SF-1809 unit and is capable of performing automated step tests (where RPM is automatically advanced in set increments while the data is recorded) and giving a friendly interface for the overall Dynamometer control from one unit. The SF-1809 is fitted with an Emergency stop system that puts the absorber on 100% load and cuts the ignition should anything go wrong. The Emergency stop system has a manual override which must be reset before the engine can be restarted.

Oil Cooler - The lack of a controllable oil cooling system led us to develop our own, by using a Setrab oil cooler mounted inside a sealed aluminum housing, a thermostat then controls the flow of pressurised cold water into the jacket surrounding the oil cooler and therefor regulates the oil temperature. Peak oil temperatures of 110 degrees Celsius are not uncommon during a power run.

Intercooler Bath - Similar in concept to the oil cooling solution, the intercooler is submerged into a bath of constantly pumped cold water, the pumps are variable speed to allow us to raise or lower the intake temperature on demand by simply supplying more or less cold water to the bath.

Simplified Water System Operation

In the above illustrations the engine stand is depicted as the dark gray framework, with a yellowed cube area showing the approximate location of the engine.

On the right hand illustration the drive-plate of the power absorber is visible, this is where the engines output (crank) shaft is connected. From the green inlet pipe leading off the illustrations the water is drawn into the gold colored main pump from the 1000 gallon reservoir, then pushed at high pressure through the green pipework into the rear of the power absorber, this water pressure is the force used to resist against the engine torque and therefore provide a method of loading the engine as if it were in use in a vehicle. Based upon the resistance inside the power absorber, the instrumentation systems can calculate how much torque the engine is producing, based upon this torque and a known RPM figure, read from the rotating load cell shaft connected to the engines crank, horsepower can be calculated.

Once the water has passed through the power absorber it is sent down the red exit pipe from the absorber unit into the reserve tank. Once the reserve tank is 75% full, the water is pumped back into the main 1000 gallon reservoir by the violet colored exit pump. A smaller subsystem of inlet pipes allow the cooling tower (not shown) to be pressurised with cold water, to be used in the exchange of heat with the engine coolant once the engine is running. Our intercooler and oil cooler systems also take a small water feed from the green inlet pipes. In comparison to the water demand of the power absorber, the volume of water draw by the cooling tower, intercooler and oil cooling subsystems is very small.

The Result

The result of our development program was a race winning 230 BHP 2.0 engine, which was reliable and powerful up to its 7500 RPM redline!

Our dynamometer is available as a facility for others to use as a tuning test bed, please ring +44 (0)1255 870636 or email if you would like to discuss your engine development possibilities with us...