Dyno On The Run
DYNOmite on-board dyno, just
about any straight stretch of pavement
can be turned into a chassis dyno.
By Dave Emanuel
Photographs by the author
The implication of an admitted dose personal relationship with horsepower is that your buddy is extremely large in stature. That isn't necessarily true because in bracket racing, the quality, not the quantity, of horsepower is a prime concern. Consequently, the ability to objectively evaluate the effect of a component change or tuning alteration can be extremely useful in a quest to reshape an engine's powercurve so the desired elapsed times can be consistently achieved while the stresses of high-rpm operation are minimized. Similar evaluation capabilities are also useful when attempting to increase or decrease power sufficiently to move up or down to a particular bracket.
Arguments can be made that the true test of a modification's effectiveness and the only result that matters-is the change in elapsed time it produces. Yet being able to correlate a horsepower increase or decrease to a specific change in elapsed time can pay consistency dividends. The problem has been that the only way to determine the amount of power delivered to the rear wheels has been to run a car on a chassis dyno. Repetitive dyno tests are time-consuming and expensive, and consequently not very common.
Conversely, if a race car could be outfitted with the appropriate equipment, every lap on a drag strip could become a dyno run. That's precisely the concept behind the DYNOmite on-board dynamometer system.
If you're an experienced racer, it will not come as too much of a surprise that horsepower doesn't actually exist; it is, in fact, a computed figure based on torque and rpm. In essence, horsepower is an engine's ability to produce torque relative to rotational speed. Every dyno measures only torque, horsepower is determined by multiplying torque by rpm and dividing by 5,252 (HP torque x rpm = 5,252).
Monitoring engine rpm is a simple task, requiring only a wire attached to the ignition coil. Measuring torque has traditionally been exceedingly more complicated because resistance must be applied to the driveline to determine the amount of force being generated. In a sense, the DYNOmite unit is a break through because it uses a non-contact strain transducer to directly measure applied torque. The DYNOmite's computer collects this data at rates up to 200 times per second, and also monitors engine and driveshaft rpm, allowing it to compute horsepower. Also unique is that the transducer does not absorb any power, so its capacity is unlimited; it can be used with any engine/driveline combination short of those that routinely spit out a driveshaft.
Installation of a DYNOmite unit is a relatively straightforward matter. Aside from connecting the harness' ground and engine rpm lead wires, the only other requirements are to mount the pickup coil on the transmission tailshaft housing and to replace the transmission yoke with the one supplied with the system (which incorporates a transducer). The pickup coil extends over the transducer, monitors its output as well as driveshaft speed, and sends the information to the system's computer, where a band of scheming semiconductors process the information.
The complete DYNOmite system consists of the transducer and pickup coil, a Rotary Interface Module, a handheld computer and the wiring harness that enables the system's components to communicate with each other. Optionally available are a thermal printer, Windows software for real-time analysis and display, exhaust gas temperature sensor, fuel flow meter and a variety of other sensors.
Operating the system is surprisingly easy. After the harness is connected to the system components and power is applied, a digital display on the handheld computer shows data as you step through the setup procedure. Three multipurpose buttons (the effect of each button is dependent on the mode in which the computer is set) on the computer are used to move from one display screen to another, turn options on or off and enter setup data. Typically, pressing the "Cal/Next" (calibration or next option) button moves an entry sequence to the next step, depressing "Print/+" decreases a setting value, and depressing "Test/-' increases it.
As a means of eliminating the accumulation of meaningless data, during setup DYNOmite requests a triggering engine rpm at which to begin recording. So if your concern is power output between 4000 and 8000 rpm, when the trigger rpm is set to 4000, you'll collect only the specific data you're after
Another means of eliminating the collection of irrelevant data is to set the "minimum output at trigger rpm" function to a specific value. Once approximate horsepower is known, this option can be used to eliminate the collection of part-throttle data. By so doing, the DYNOmite can be set up to record before doing a burnout so the driver's attention isn't diverted from starting-line activities.
A third qualifier is "minimum speed to maintain recording." This value, which must be set below the trigger point, terminates data recording once rpm drops to the specified level. If the trigger value is set to 4000 rpm and minimum speed to maintain recording is set at 3500 rpm, a graph of the recorded data will begin at 4000 rpm and continue through the maximum engine speed reached back down to 3500 rpm.
For example, if the unit was set up to trigger at 4000 rpm and 350 horsepower, it could be turned on prior to doing a burnout, but wouldn't start recording data until after the car left the starting line. Most sane people don't go to wide-open throttle during a burnout, so even if rpm exceeded 4000, the 350-horsepower threshold would not be reached.
After data is collected, it may be viewed on the computer's display screen or be printed out on the optional thermal printer. Another option is to download the information to a laptop or desktop computer for viewing and analysis. Primary advantages of the DYNO-MAX software include graphing and animation capabilities. Puffing up the playback dashboard fills the screen with analog-type gauges that are simulations of a speedometer, tachometer, g force and gear ratio meters. Also displayed are cyber gauges showing engine temperature, manifold pressure, fuel flow and brake specific fuel consumption.
When viewing the "dashboard," the entire run can be played back, and the gauge needles move as they would have during an actual test. Should a specific point of interest demand more detailed consideration, the display can be frozen. And if you missed it the first go-around, the rewind button allows you to start again from the beginning.
Similar capabilities are available when a dyno-cell console, rather than a dashboard display, is selected. Since it's designed to mimic the console of an engine dyno, the console gauges consist of a tachometer and torque analog gauges. Horsepower and rpm are also displayed digitally, and the engine temperature, manifold pressure, fuel flow and brake specific fuel consumption analog gauges are also displayed.
When commanded to graph, the DYNO-MAX software plots horsepower and torque relative to rpm. Analysis is further enhanced by the ability to overlay graphs from several runs, so the differences can literally be seen graphically. Since the DYNOmite system records all data after the trigger rpm (and also after the minimum recording rpm), the graphs are a bit unusual in appearance because some amount of data is recorded during deceleration. On both the graph and tabular data, this is rather obvious, so it can be easily ignored.
While a graph enhances the presentation of the overall picture of an engine's powercurve, actual data is also useful in making an analysis. With DYNO-MAX hard numerical data can be viewed by telling the program to show key data points. The resulting table, which can be viewed on the screen or printed, looks very much like the printout that's provided by most computerized engine dynos.
Although the DYNO-MAX software significantly enhances the system's data presentation and manipulation capabilities, it's by no means a requirement. Valid, meaningful data can be collected and analyzed using only the basic DYNOmite system. A printer makes life easier, because without one, producing a hard copy for future reference is difficult.
As with any kind of test equipment, questions exist as to the DYNOmite's accuracy. Had the opportunity presented itself, we would have run the vehicle on which the system was installed on a chassis dyno and compared the results. That's a possibility for the future, but based on the data recorded and actual elapsed time and trap speed, the DYNOmite appears to be very accurate. Now if we can just find a way to cut a perfect light every round, we'll really bring a smile to our faces. ET
Figure #1 - Leaving the line with its wheels in the air, our late-model Camaro puts the DYNOmite on-board dyno system to the test. Horsepower figures recorded by the unit closely matched what the engine actually produced as indicated by elapsed time and trap speed.
Figure #2 - The DYNOmite systems consists of a handheld computer with four buttons and a small display screen, a rotary interface module, transducer (which is mounted on the driveshaft yoke) and a pickup coil. A thermal printer is a worthwhile option.
Figure #3 - The transducer/yoke supplied with the system replaces the standard yoke that couples the driveshaft to the transmission. The pickup coil is clamped to the trans tailshaft housing and extends over the transducer.
Figure #4 - When the handheld data computer is turned on, the screen displays torque, power and engine speed. Pressing the "Cal/Next" button changes the display to allow selection of the next desired operation. Pressing the button again moves the computer into setup mode.
Figure #5 - The first option is the speed at which the built-in rev limiter is to be set. Pressing the "Test/+" increases rpm; pressing the "Print/-" button decreases it. Pressing the "Cal/Next" button brings up the next setup option.
Figure #6 - Since the DYNOmite displays corrected horsepower and torque figures, current temperature, humidity and barometric pressure information must be entered.
Figure #7 - While the system is operating, and also in playback mode, torque, horsepower and engine rpm are displayed on the screen, along with the elapsed time since data recording began.
Figure #8 - The dashboard console is another option for viewing and analyzing data. Rather than torque and horsepower, the cyber-dashboard displays vehicle speed, g force, gear ratio and engine speed. Gear ratio function is actually a correction factor to compensate for transmission gear ratio.
Figure #9 - DYNO-MAX software offers a variety of displays for viewing and analyzing data. The playback console is a simulation of an engine dyno console with a variety of gauges and digital read outs. Boxes in the lower left-hand comer allow a dyno run to be played back, stopped or rewound. During Pay mode, the gauges move to reflect the values recorded during each particular frame.
Figure #10 - The big picture of an engine's horsepower and torque output is most easily viewed in graphical format. The DYNO-MAX software can graph either single or multiple runs, making It relatively easy to compare powercurves from different runs. The horseshoe shape of the powercurves is a result of data being recorded as a car is decelerating.
Figure #11 - Sometimes, there's no substitute for hard numbers, so DYNO-MAX offers an option to display data in tabular form. The data can also be printed, so a hard copy can be kept on file for future reference.