On the Road Dyno

Aim Solo showing Lambda

Using a lambda sensor as an on board dyno 

Most of us get our race engines tuned on a  dyno at  some stage and it is normally one of the more exciting days of a race car build. By its nature this tuning does not hapen very often. What about all the running time you have between dyno sessions ?

 

The rolling road 

The rolling road dyno has two key tools -  the measured load on the car and the the air - fuel meter.  If we load up the engine on the road or race track and measure  the air / fuel ratio can't we achieve the same thing  ?  We can't print out a nice power curve but we can improve the tune of the engine.

The lambda sensor

A lambda  sensor  measures the difference between the oxygen in the atmosphere and the oxygen in the pipe. This difference produces a very small voltage which needs to be looked after and turned into a sensible signal. While doing this the controller also heats the sensor and  maintains the correct temperature. So the controller has the job of maintaining the correct temperature,  and conditioning the signal. 

This lambda controlling task is done inside some ECUs like the Motec M800 or the Pectel SQ6. However the current trend is to reduce the size of the ECU and put the controllers outside the ECU.

The ECU  has the unenviable job of fuelling the engine under a variety of conditions, the main parameters being throttle angle and rpm. Other influences are many, engine temperature, air pressure, intake air temperature, and many more to what ever sophistication the ECU can handle. 

All these influences go into the engine along with fuel quality and timing  to produce a lamdba value we can record and inspect. 

If I am attending a dyno session I observe the dyno  air / fuel meter and I always have at least one lambda sensor properly mounted in the exhaust pipe. The sensor should be being about a metre away from the head in a sealed exhaust pipe. This is the ideal position. I have worked with a well known touring car engine builder who was obsessed with having a completely sealed exhaust front to rear just so they can rely on the lambda sensor being accurate. Any gaps in any joints can suck air that dilutes the exhaust and gives an incorrect reading.

The Datalogger

The importance of recording all this can't be stressed enough. There is too much going on, too many influences not to have a proper record of all this activity. A lambda controller without a datalogger is like a formula one car without a rear wing. 

Often the ECU is a very good datalogger,  but there are many being used today that have no memory or are expensive to upgrade. Some of the current ECUs no longer have lambda controllers built into them. So this is where a standalone controller like the Aim LCU One  can control the lambda heater, and send a signal to the datalogger. The signal can go into to an Aim dash logger or into an analog channel in the ECU. 

The on road dyno has many benefits. Getting part throttle or transient  conditions  is difficult and time consuming  on a dyno. Most dyno runs are done at full throttle because it is easy and  the customer wants a power curve ! Making the car drivable is more important and this is best done in real world driving conditions - making a data logger one of the best tools in your racing arsenal. 

The LCU One

The LCU One is a small controller connected to a power supply and a Bosch 4.9 wideband lambda sensor. The 4.9 sensor is a cheap and robust sensor compared with sensors used in the past. It can tolerate abuse and a wide range of fuels, even 2 stroke and diesel. 

On the track dyno operation

The screen shots below are from my BMW with a 2.5 litre M20 engine on the front straight at Taupo race circuit.  It has a standard ECU with a modified eprom that can go another 400rpm over standard. As  the chip has been modified I suspected the tuner will not have missed the opportunity to throw some more fuel at it. 

The equipment used was an Aim Evo 4 logger and an Aim LCU One lambda controller using a Bosch 4.9 sensor. The data is as simple as possible,  just rpm and Lambda. 

It turns out that the engine tune can stand some improvement !

Perfect air / fuel ratio of 14.7 : 1  is represented  by lambda 1.0  Peak power is around 0.9,  superior fuel economy  any where above 1.0 

The areas in question are down the straight  so we can assume full throttle, a similar situation  to what we see on most dyno runs. 

Graph one. The lower trace in red is the lambda. The graph range is between 0.75 and 1.0.  The black trace is rpm between 3 and 7000 rpm. The red lambda trace  wobbles in a S curve, generally rich ( around 0.83 ), gets richer,  and leans off as the rpm rises.  The leanest it ever gets is .88 or .89.  This confirms my suspicion  that the tuned chip, has just had more fuel put into it.

Graph two.  The excessive  richness is particularly bad at 4800rpm. This is  the first place to start  when retuning this ecu.  

This is a deliberately very simple example how your on board dyno can be used to tune your car with real world data. Even if you don’t map the ecu your self this gives a tuner or a dyno operator so much information to start  with you should require fewer runs on the dyno. 

More detailed analysis with for example part throttle or manifold air pressure  will give added information making for informed changes to the ECU's fueling map. Particular attention should be paid to the first 20 % of throttle opening as this is the area of the map the the driver really feels,  trying to get response and a smooth transition onto power mid corner.

For more information on the Aim LCU One  go to  the Aim website -  Aim LCU One 

Lambda trends
Lambda trends
lambda low points
lambda low points