Tuning with Durametric: a primer
 

I was unable to find a comprehensive FAQ specific to the use of Durametric in our vehicles. My previous FAQ was simply a collection of previous threads. Since it is a very useful tool that helps measure tuning efficiency and safety, I thought it would be useful to begin a discussion about using Durametric to tune by proxy - a technology that wasn't available years ago is now readily available due to OBD flashing.

I hope other members can chime in. If any tuners can participate, I would appreciate your constructive input as well.

A few useful threads to start with:
https://www.6speedonline.com/forums/...a-logging.html
https://www.6speedonline.com/forums/...se-advise.html
Durametric what to log
The Official- How to use your Durametric
Logging Timing in the Durametric?
What ignition angle (aka advance) are you seeing?
Failed my emission test, what can be done?
Data logging?
MAF - how to diagnostic by Durametric


Things to log:
The three parameters in a turbocharged vehicle that are adjusted and optimize to maximize performance are ignition angle (timing), AFR (lambda), and boost.

Ignition angle
Timing advance.

The period between the spark firing and the complete combustion of the fuel/air mix is very short...ignition must take place early enough for the peak pressure caused by the combustion to occur just as the piston has passed TDC, as the piston falls down the cylinder bore. If ignition occurs early, the piston will slow as it moves toward TDC. If it occurs too late, the piston will already be moving downwards, wasting the energy created during combustion.

If the spark occurs very early, the ignition pressure wave can ignite the mixture in various parts of the combustion chamber, causing detonation.
If the composition of the mixture were constant (it isn't), the elapsed time between ignition and full combustion would be constant. If the ignition advance angle were set at a fixed angle before TDC, combustion would shift further and further into the power stroke as RPM increased. The faster moving piston would be further down the bore by the time combustion actually occurred. To prevent this, the ignition advance must increase as RPM rises.

In addition to engine speed, the other major factor affecting the amount of advance required is the engine load. At light loads, when lean mixtures are used, the speed of combustion is slowed so more ignition advance is needed. Other factors are also relevant:

• Design and size of the combustion chamber
• Cam timing
• Position of the spark
• Fuel
• Emissions levels required
• IAT
• Margin of safety

The emissions of an engine will be affected by the ignition timing, in addition to the AFR. Oxides of nitrogen increase as ignition timing is advanced. If emissions standards need to be met, this advance may have to be reduced. The emission of CO is not really affected by ignition timing...more so by the AFR. Hydrocarbons at stoichiometric and rich AFRs increase with advanced timing, but now when the engine runs lean.

It's impossible to answer the question "what ignition timing is best?" Only real-time dyno'ing, datalogging, and knock detection can we see how the ignition timing influences emissions, power and fuel economy.

Actual lambda value bank 1 and 2
Lambda reading in front of the catalytic converter.

Proper AFR calibration is critical to performance and durability of the engine and it's components. The AFR defines the ratio of the amount of air consumed by the engine compared to the amount of fuel. The turbochargers increase the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of detonation. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock.

As a protective mechanism, the ECU is designed to make the AFR richer, reduce boost, and/or retard ignition timing to prevent catastrophic detonation, but also diminishing performance. These parameters need to be optimized to give the best performance with a margin of safety for the engine.

Rich versus lean, why lean makes more power but is more dangeros
A stoichiometric AFR has the correct amount of air and fuel to produce a chemically complete combustion event. For gasoline engines, the ratio is 14.7:1, which means 14.7 parts of air to one part of fuel. This ratio is dependent on fuel type-- for alcohol it is 6.4:1 and 14.5:1 for diesel.

Durametric reports lambda - a percentage of AFR based on the stoichiometric ratio. To report the proper AFR from Durametric, multiply the pre catalytic actual lambda by 14.7. For example, a lambda of 0.78 gives a AFR of 11.47:1 (0.78 * 14.7 = 11.47.)

<dl><dd>http://upload.wikimedia.org/math/b/b...88d38b383e.png</dd></dl>

In general, a lower AFR number contains less air than the stoichiometric AFR - hence the mixture is richer. A higher AFR number contains more air and therefore it is a leaner mixture.

For Example:
15.0:1 = Lean
14.7:1 = Stoichiometric
13.0:1 = Rich

A lean AFR results in higher temperatures when combustion occurs

Turbochargers increase the density of the air resulting in a denser mixture. As the air-fuel mixture is ignited by the spark plug, the explosion propagates from the spark plug raising cylinder pressures as well as overall temperature.

The denser mixture raises the peak cylinder pressure, increasing the probability of pre detonation, or knock. As AFR is leaned out, the temperature of combustion also increases, which also increases the probability of knock. This is the ECU is programmed to run richer AFR as boost increases during full load. A richer AFR reduces the temperature and likelihood of knock. These physical principals are a fundamental difference between a naturally aspirated and a turbocharged engine.

When temperatures or peak cylinder pressures rise beyond engine specifications, the Motronics is designed to protect the engine by manipulating 3 parameters: reduce air density (boost), adjust the AFR to richer mixture, and retard ignition timing. These three parameters need to be optimized together to yield the highest reliable power. A well tuned engine will optimize these parameters to yield greatest power while protecting the engine from damage. A poorly tuned engine may sacrifice safety parameters to achieve greater power, but lead to catastrophic failure after multiple laps lead to heat saturation.

Pressure ahead of thr. Plate press. Sensor.
Boost during WOT is not directly measured. You need to calculate the value based on ambient atmospheric pressure.

"Boost pressure of sensor" is an actual value, and it is displayed in milibars. Ambient pressure needs to be recorded as a constant. Under acceleration, the sensor reading needs to b e corrected with the ambient pressure constant.

For example, 990 milibar at idle, means 990 milibar atmostpheric pressure. At WOT (6734 RPM), I record 2178.75 milibar.

2178.75 - 990 =1188.75 milibar = 1.18 BAR

Setpoint Boost Pressure
Requested boost in milibar.

Injector duty cycles
Duty cycle = Injector time * RPM / 1200
(time ms)*(0.001 s/ms)*(RPM rot/min)*(1/60 min/s)*(1/2 intake/rev)*100%

Engine speed
Records the reference RPM at which the events are recorded. RPM is corrected (filtered) engine rpm. This should match the tachometer in the dash very closely.

Engine load
A calculation of airflow and RPM. While it's more complicated than that, its basically the main reference when referencing stored tuning data. For example, 100% is basically a calculation of 100% of cylinder volume being filled with air.

Injector time
You can compute injector duty cycle as: Injector time * RPM /1200 the answer is in %. This gives you a measure of how well your fueling is keeping up.

Actual throttle plate angle

MAF
Mass air flow (HFM), a measure of air flow. This will be actual airflow on stock cars, but may not be accurate on tuned cars, and useless when running MAFless.

IAT
The estimated limit before the ECU begins pulling back on timing advance and fuel mixture on the Mezger engine is ~50-55C.

EGT

Thanks Bob. Is there a consensus about what constitutes a "safe" lambda value?

Great thread, Bob. Bookmarked for reference;)

I'm by no means an expert. I'm hoping to get a few more experienced guys on board to help fill in the blanks.

Safe lambda depends on your setup. I typically view 1 for idle, for load, 0.78-0.83 range.

Great thread Bob. I wish I had this when I was first getting started. Would have saved me a lot of time. Some input from Tuners would be terrific.

I vote Sticky!

This definitely needs to nee a sticky

+1 Totally agree!

+2
with Durametric coding list included for those that have the professional version

Can you belive that my Porsche dealer quoted me 150€ to make my side turn signals blink?

can u log actual vs requested boost? wouldnt this be useful in finding a boost leak?

Yes, but is not very useful for that purpose.

Updated definitions. Fellas, contribute as you see fit.

+1 thanks for posting this Bob

It appears that EGTs logged from durametric are actually modelled EGTs and not actual. I am not sure whether actual temps can be logged somehow?
Also I am using lambda of .85-.87 with very good results and reliability. My tuner insists that this is how racing turbo P cars run all day long at the track..
Also can we detect knock somehow through the actual data?

Isn't this the EGT sensor?

http://www.picvault.info/images/537023562_IMG_2452.JPG