DeltaDash On-Road Dyno Testing
EcuTeK DeltaDash Road Dyno feature (from hereon abbreviated to DDRD) allows real life performance testing of any manual transmission Subaru vehicle supported by DeltaDash. This enhancement to DeltaDash is a free upgrade available to new and existing customers via software download from the EcuTeK web site. No hardware is required, other than the standard hardware supplied with DeltaDash.
In addition, due to the way the DDRD does its calculations, it is unaffected by any piggyback ECUs or speed delimiter modules.
How it works
DDRD measures engine speed reported by the ECU, many times per second. Based on this, and additional data about the car, such as tyre, gearbox, drag and weight, DDRD can calculate many statistics about the vehicle's performance, based on a simple full throttle in gear test of the engine on the road surface of choice.
DDRD will calculate the following statistics:
Wheel power and torque. Peak figures are displayed, plus graphs.
In gear acceleration times e.g. 30-50, 50-70, 70-90mph.
Vehicle acceleration in graphical form.
See best gear shift points. By plotting vehicle acceleration against vehicle speed for a number of gears, you can see the ideal speed at which to change gear.
Terminal velocity due to power developed. A vehicle stops accelerating at the point where the power produced by the engine equals the power consumed by the drag on the car. This useful feature calculates the maximum achievable vehicle speed, assuming ideal gearing,
DDRD will also compare up to 4 tests simultaneously, which allows comparison of the performance of different gears, cars and states of modification.
Using DeltaDash Road Dyno
Use of DDRD is very simple. Before driving the car, the software must be setup with various physical characteristics of the vehicle in question, such as tyre size, gearbox type, rev limit, mass and drag data. These vehicle characteristics may be selected simply from lists of available options for the various car models. As long as you know the model of car you are driving, this is very simple to do.
Once this data has been entered, DDRD will display a graph showing the vehicle speeds achievable in each gear. This is as much as DDRD can tell you about your car until you perform an in gear test of the engine - see below.
Gathering performance data about the vehicle involves driving the vehicle from low engine revs (say 1000 RPM) up to any higher RPM that you choose. Before testing, ensure that you have selected the gear you have decided to test in - this is labelled 'Test Gear'. To perform the test, select the 'Setup & Data Capture' tab and from a steady cruising speed, when you are ready, click on start test. You must then reduce speed until the engine drops below 1250 RPM. Once the engine revs have dropped low enough, the test will begin. At this point, the driver must accelerate in the chosen gear. No gear changes, braking or clutching should be performed during this test - the test is from low revs to high revs in a single gear.
This will require two people - one to drive and one to operate the laptop. Do not try to do this alone.
Viewing Results Graphs
Once the performance test has been done, clicking on the 'Data Analysis Graphing' tab will display a vehicle performance graph. The axes of this graph may be altered to show a wide variety of statistics. The most common graph for comparing vehicles will be Power & Torque against Engine RPM or Vehicle Speed. Preferred units of measure may be selected at any time - Power in BHP, PS or kW, torque in Nm, LbFt or kgm. When viewing power & torque, the power is the bright line, whilst the torque is the more feint line.
Viewing Results Statistics
Selecting the next tab, 'Performance Report' shows various facts and figures about the car. These may be cut & pasted for use elsewhere.
Test data and the entered vehicle characteristics may be saved at any time using the 'Save Data...' button. Files may then be reloaded and edited using the 'Open Data File' button - this allows editing of the vehicle characteristics, should any previously entered data be found to be incorrect.
Up to four data files may be viewed simultaneously by using the 'Compare Files' panel to load in three further data files. The colours of each graph line is shown next to the name of each file loaded.
Getting Accurate Results
It is absolutely essential that the correct test gear is chosen in order to get accurate results. Using 'Test Gear', you must select the gear in which the test was performed.
Tyres & Gearbox
Since DDRD uses engine RPM data to calculate vehicle performance, the characteristics of the gearbox & tyres must be specified so that DDRD can translate measured engine RPM into the correct vehicle speed. Tyre data is easy to ascertain. Simply look at the tyres on your car - they will have their dimensions printed on the side wall. Gearbox data, unless you've been doing serious modifications to your car, will be the same for all cars of a particular model - simply select the correct model from the list. If you have modified your car's gearbox, then you are the only one who should know this information!
In order to calculate the power & torque that the engine is generating based on this speed data, DDRD must also know the mass of the car - it is important to get this figure accurate, since the calculated power will vary in proportion to the mass entered. The mass specified should be the current mass of the vehicle at the time of the test.
The following variables will affect the current vehicle mass:
Number of occupants
Fuel tank level
Modifications e.g. replacement exhaust, roll cage etc.
Any items being carried in the car.
The book kerb weight should not be used. Get your vehicle weighed with a known amount of fuel in the tank. This may be done at a weighing bridge or by using corner weight scales for a really accurate reading.
Overestimating the vehicle mass will give a power figure that is too high. Underestimating the vehicle mass will do the opposite.
DDRD takes into account aerodynamic drag when calculating engine performance. Vehicle drag co-efficient and frontal area are the parameters required to calculate power lost to aerodynamic drag. Whilst important for accurate power calculations, these vehicle characteristics are far less important to measurement accuracy than the vehicle mass. Aerodynamic drag is quite small in 2nd & 3rd gear and so inaccuracies in these figures will only result in a small (2 or 3 BHP) error in calculated power. If power tests are performed in higher gears e.g. 4th, 5th or 6th, then the importance of these values becomes much greater. In the absence of definitive data, use a frontal area of 2.2 sqm and a drag co-efficient of 0.35.
The ECU's rev limit is only relevant when calculating the maximum speed possible in each gear. It is not used for any other performance calculations. Unless your car's ECU has been modified, then simply select the rev limit matching the model of your car.
Comparison of Road Dyno & Chassis Dyno Power Testing
DDRD gives real world performance figures - plain and simple. There is no disputing performance figures that are calculated on the road, in the true driving environment. There are many variables that effect the results of power testing for both chassis (rolling road) and on road dyno testing. These include:
Air temperature - when road testing, this is the temperature out on the road. When rolling road testing, this is the temperature found inside the building. Depending on the complexity of the rolling road, it may be possible to regulate air temperature (e.g. MIRA), but dynos with this facility are well beyond the budgets of enthusiasts.
Intercooler cooling effect - greater cooling effect means denser charge air, more power, faster spool up and larger boost spikes.
Coolant system cooling effect - greater cooling effect enables better regulation of engine temperature.
Exhaust cooling effect - greater cooling effect of exhaust manifold/headers worsens turbo spool up due to reduced exhaust gas velocities at the turbo.
Load impedance - this determines how fast the engine is allowed to accelerate. On the road, this is determined by the gearing, drag and vehicle mass. On the rolling road, this is determined by the dyno operator and the setup of the rolling road. On a rolling road, perform the test too quickly, and the turbo spool up will be inaccurately poor and the car will not achieve a high enough boost pressure. Perform the test too slow, and the turbo spool up will read unrepresentatively high and heat build up will impair the top end power figure.
This is one of the main reasons why comparing results from two dissimilar dynos is a waste of time. It is meaningless to say that one dyno 'reads' higher or lower than any other dyno unless the characteristics of the test are known, and the effect of these characteristics is known and understood.
Wheel slip - on a rolling road, it is normal to test vehicles in quite high gears. This helps to reduce wheel slip on the knurled steel rollers on which the car sits. When road testing, there are higher levels of friction between the tyres and road surface, which allow tests to be performed in lower gears if required.
When testing on the road, you know that the above variables are all real world quantities encountered on the road. Only if the operator of the rolling road can reproduce all of these effects as seen on the road will the rolling road performance figures be close to those actually encountered on the road. Having said that, in order to get accurate results using a road dyno method, it must be setup correctly, though this is much easier to achieve.
Power Engineering assisted in the development of this product. Power runs of the development vehicle were taken on the rolling road. A figure of 227 wheel horse power was produced in 4th gear. Out on the road, using DDRD, figures of 222 & 233 horse power were produced in 2nd & 3rd gears respectively. From this test, it is clear that both methods of testing can produce very similar results. It is worth noting that Power Engineering have extremely powerful cooling fans on their rolling roads - these fans help to mimic the air flows seen on the road. They are so powerful that walking in front of these fans can make you lose your balance - it is worth checking the cooling equipment that is employed by your chosen rolling road test centre, since this can have a significant effect on results.
For various technical reasons, it is not possible to accurately calculate flywheel horsepower using using DDRD. All performance figures are quoted in wheel power & torque - the actual power seen at the wheels. Most rolling roads are able to calculate flywheel horsepower reasonably well - this is one reason why a visit to your local rolling road is worthwhile. Having said that, it is wheel horsepower that is relevant to the real world - this is the power that the vehicle is putting down onto the road. Just don't get flywheel and wheel power confused. If you get quoted two power figures, the wheel power is always the lower of the two.
Disclaimer & Safety Considerations
DDRD should only be used on private roads and test tracks. Under no circumstances should the product be used on the public highway or in any other situation where its use may break speed limits or contravene any laws. EcuTeK take no responsibility for inappropriate use of the product.