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DeltaDash On-Road Dyno Testing

THE ECUTEK DeltaDash Road Dyno feature (from hereon abbreviated to DDRD) allowthe 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.

Statistics

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 gearshift 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 four tests simultaneously, which allows comparison of the performance of different gears, cars and states of modification.

Using DeltaDash Road Dyno

Setup

DDRD use is very simple. Before driving the car, the software must be setup with various physical characteristics of the vehicle in question, such as its tyre size, gearbox type, rev limit, mass and drag data. These vehicle characteristics may be selected from lists of available options for the various car models. As long as you know the model of car you are driving, this is straightforward.

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).

Testing

Gathering performance data about the vehicle involves driving the vehicle from low engine revs (say 1000rpm) up to any higher speed that you choose. Before testing, ensure you have selected the gear you have decided to test in, which is labelled 'Test Gear'.

To perform the test, select the Setup & Data Capture tab and, from a steady cruising speed, click on Start Test as soon as you're ready. You must then reduce speed until the engine drops below 1250rpm; once the engine revs have dropped low enough, the test will begin. At this point the driver must accelerate in the chosen gear; no gearchanges, braking or declutching should be performed during this test, which is simply one carried out from low revs to high in one solitary gear.

This will require two people: one to drive and one to operate the laptop; do not attempt 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 whose axes may be altered to show a wide variety of statistics. The most common graph for comparing vehicles will be of power and torque against engine speed or vehicle speed. Preferred units of measure may be selected at any time, power in bhp, PS or kW, torque in Nm, lb ft or kgm. When viewing power and torque, the power is the bright line, the torque the fainter line.

Viewing Results Statistics

Selecting the next tab, 'Performance Report' shows various facts and figures about the car. These may be cut and pasted for use elsewhere.

Saving Results

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.

Comparing Results

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 the graph plots are shown next to the name of each file loaded.

Getting Accurate Results

Test Gear

If you want to get accurate results it is absolutely essential that the correct test gear is chosen. Select the gear in which the test was performed by selecting 'Test Gear'. 

Tyres and gearbox

Since DDRD uses engine RPM data to calculate vehicle performance, the characteristics of the gearbox and tyres must be specified so that DDRD can translate measured engine RPM into the correct vehicle speed. Tyre data is easy to ascertain as the dimensions are moulded on the tyre sidewall. Gearbox data, unless you've been doing serious modifications to your car, will be the same for all cars of a particular model, so simply select the correct model from the list. If you have modified your car's gearbox you will presumably know its relevant specs. 

Mass

In order to calculate the power and torque 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 aboard, eg 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.

Aerodynamics

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. While 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 second and third gears, so inaccuracies in these figures will only result in a small (2 or 3bhp) error in calculated power. If power tests are performed in higher gears, though, such as fourth, fifth or sixth, these values take on much greater importance.

NOTE: In the absence of any definitive data you should use a frontal area of 2.2sqm and a drag co-efficient of 0.35

Rev Limit

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.

Road and Chassis Dyno Testing Compared

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. But 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 inside the building. Depending on the complexity of the rolling road, it may be possible to regulate air temperature, but dynos with such a facility are usually well beyond the budgets of private enthusiasts
  • Intercooler cooling effect greater cooling effect means denser charge air, so 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 it is determined by the dyno operator and the setup of the rolling road. On a rolling road if you 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 slowly and the turbo spool-up will read unrepresentatively high and heat build-up will impair the top-end power. 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 another dyno unless the characteristics of the test are known and the effect of these characteristics is understood.
  • Wheel-slip on a rolling road it is normal to test vehicles in quite high gears as it helps to reduce wheel-slip on the knurled steel rollers on which the car runs. When road testing though, there are higher levels of friction between the tyres and the road surface, whch fact allows tests to be performed in lower gears if preferred.

When testing on the road, you know that the above-mentioned variables are all real-world quantities encountered in reality. The rolling-road performance figures will onbly be close to those encountered on the road only if the rolling-road operator can faithfully reproduce all of these road conditions. Having said this, in order to obtain accurate results using the road dyno method, it must be set up correctly, although 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 227whp (wheel horsepower) was produced in fourth gear. Out on the road, using DDRD, figures of 222 and 233 horsepower were produced in second and third 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, which help to mimic the types of airflow usually encountered on the road. These fans are so powerful that walking in front of them can make you lose your balance; it's worth checking up on the cooling equipment 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 DDRD. All performance figures are quoted as wheel power and wheel torque ‒ the actual power delivered by the wheels. Most rolling roads are able to calculate flywheel horsepower resonably well, and this is one reason why it's worth making a visit to your local rolling road. Having said that, it's the wheel horsepower that is more relevant, as it's the power the vehicle puts down onto the road. Be careful not to get flywheel power and wheel power confused, and if you're quoted two power figures be aware that wheel-power is always the lower value.

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 whatsoever for the inappropriate use of this product.

 

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