Category Archives: Testing

Brake, Testing

Braking Distance Check

Next on the agenda is looking into changing the ABS setting for the front brake bias to see if there’s any discernible change in the car’s braking distance.

I got started today recording a couple of braking events, starting and 60 mph and slowing to a stop, or just about stopped.  So that I can conduct this exercise more easily I record the ECU data using ME7Logger and then the time stamp and vehicle speed to find the distance travelled.  The results using this method may not be valid for comparison with tests where a true distance measurement is taken, but in the interest of getting some results to look at I’ve chosen this method.

The time and speed data is crunched via an excel macro and the distance is calculated, along with an estimate for g-force’s during the deceleration.

The first two test runs are shown on the two charts below:

Brake Check 1
Brake Check 1
Brake Check 2
Brake Check 2

To check for consistency I plotted the distance versus time for the two test trials.

Trial Results Compared
Trial Results Compared

Those are clearly NOT consistent results.  I will need to make a few more trial runs before I have enough baseline data to feel confident about moving on to recording comparison data with the RS4 brake bias setting.

This chart also reinforces my belief in making multiple runs to get a number of data points to consider.  All too often I read about tests being performed where a single reading is taken before, and then a single reading taken after, with the results being presented as definitive proof of a change, or lack thereof, attributable to the one variable (out of many) that the tester chose to consider for monitoring.

Returning to the test I performed.  I began at sixty miles per hour and decelerated to close to 0.  When the readings start to get near to zero it seems that the data value from the ECU becomes very small, but zero is not reported.  This creates errors as it leads to calculating additional distance traveled that may not be occurring.  My solution to this limitation in the measurement system is to call 1 mph close enough to zero to be the stopping point.

For the purposes of the check I am interested in, whether adjusting the ABS bias improves braking performance, my hope is that this measurement challenge is mitigated by being able to compare several curves and that the trend line will be indicative of a change, or no significant change.  This would lessen the importance of the overall distance measurement.

The next step in the test is here.

Testing

AWE-Tuning Exhaust Manifold Backpressure

With the affect of the AWE-Tuning tubular exhaust manifolds on boost onset measured I moved on to recording the pre-turbine exhaust pressure.

AWE-Tuning Tubular Exhaust Manifold Exhaust Backpressure
AWE-Tuning Tubular Exhaust Manifold Exhaust Backpressure

These readings confirmed what I suspected, that the pressure near the turbine housing inlet would be greater with the AWE manifolds installed.

The reason the pressure is increasing is that the AWE manifolds create less of a restriction in the exhaust path.

awe_exhaust_manifold_diagram

Using the picture above to illustrate what is taking place, the pressure in the cylinder following the combustion process is high (P1), and unaffected by the exhaust manifold.  As the gasses travel through the manifold friction and changes in direction cause the pressure to drop, so that when the gas reaches the inlet to the turbine housing, the gas pressure is lower (P2).

When the stock exhaust manifolds are used there is a greater loss of pressure, and since the pressure at P1 is the same regardless of the exhaust manifold, then the pressure at P2 will be lower with the stock exhaust manifold than with the AWE manifold.

Looking at it from a different angle, if the pressure a P2 is some value with the stock manifold, when the AWE manifold is installed the value of the pressure, P2, should be greater, which is what is shown by the chart.

What remains to be seen is how much, if any, affect this reduction in exhaust manifold pressure loss has on the engine’s volumetric efficiency.  Hopefully the DynoJet will be able to answer that question.

Testing

K04 vs 770 Torque Curves

The chart below compares the aggregate wheel torque from dyno charts of (4) BW RS4 K04 equipped B5 S4’s against that of (6) TiAL 770 equipped B5 S4’s.

Note: Any time that data is recorded on different vehicles it’s expected that the results will be different between the vehicles.  To attempt to mitigate this variability I prefer to use averaged data, when available, since I believe it is more representative of what an individual owner may achieve if they were to equip their own car with similar components as the vehicles being measured.

The intent of the chart is to show how one aspect of the vehicle performance compares between cars equipped with significantly different turbocharger hardware.

Note:  More than just turbocharger hardware differs between the vehicles, but the large majority of performance difference can be attributed to the turbocharger being used.

The specific attribute this chart addresses is how peaky the engine torque curve is, measured at the wheels on a dyno.  That is, how rapidly torque builds and how rapidly it then drops off.  Between these two turbochargers the 770 is the larger, this normally results in a torque curve that is shifted to the right, and is greater, than a vehicle equipped with a smaller turbocharger, such as the BorgWarner K04.

Wheel Torque Curve for BorgWarner RS4 K04 vs TiAL 770 equipped B5 S4's
Wheel Torque Curve for BorgWarner RS4 K04 vs TiAL 770 equipped B5 S4’s

That trend holds for these two turbochargers whose baseline values are shown with solid lines.

To get an idea of how peaky one turbo is versus the other I have shifted the BW K04 torque curve to the right, and up, transposing the values so that the shape of the curve is retained but the location on the chart is different.

As shown by the dashed red line and solid blue line, the torque curves for the BW K04 and TiAL 770 are quite similar.  Whether one chooses to define this shape as ‘peaky’ or not is something I won’t attempt to answer.

It’s important to emphasize that the two turbochargers would feel quite different from the driver’s seat on account of the location of the curves on the chart.