Why you need it, and what you need to know.
Why is data logging so important?
Imagine trying to drive a car with your eyes closed. Not smart, huh? This is the same situation when tuning a performance car with out something called data logging. What is data logging? Data logging is the ability to view all major parameters that relate to engine operation. Some of these parameters are engine rpm, coolant/air temperature, engine load (psi), air/fuel, injector duty cycle, throttle position, vehicle speed, etc. All of these parameters can help you get the maximum performance for a given application, as well as be vital in trouble shooting issues that arise. At the drag strip or road course track data logging is invaluable, as it lets you see exactly what happened during a run or track time. Data logging can show something as simple as boost leak, being to rich/lean, or not being full throttle which can have a huge impact on mph and e.t. Data logging gives you the ability to compare runs, and make changes to the tune or other settings based on results. It will also allow you to monitor all the engine vitals (sensor information like fuel pressure, oil pressure, knock sensor, etc) so that you can evaluate if the engine is running in a safe condition during racing. You can achieve much greater results in much shorter time when having as much information as possible on engine/car performance.
What are some important engine performance and reliability parameters?
Some of the most important parameters to data log for engine performance and reliability are fuel pressure, oil pressure, air/fuel, exhaust gas temperature, knock sensor, exhaust back pressure and oil temperature. Each of these parameters gives vital information on what is happening with an engine, and will help tremendously with trouble shooting and ensuring consistent, reliable engine performance.
Fuel pressure shows you the pressure that the fuel system is operating at. In a turbo application you need the fuel pressure to rise at a 1:1 ratio with intake manifold pressure. If this does not occur, either you will prematurely use all available flow from the fuel injector or cause the engine to "lean out" and not operate at the desired air/fuel ratio. Monitoring fuel pressure can also help diagnose potential fuel pump, regulator or filter failure, as well as wideband sensor failure.
Oil pressure shows you the pressure that the engine is operating at. If the engine is low on oil pressure, damage to the bearings and other essential components can quickly occur. Monitoring this parameter will ensure the oiling system is functioning properly.
Air/Fuel shows you the amount of air to parts fuel in the exhaust stream. This is essential for optimal performance, as well as keeping engine combustion temperatures within safe levels. Too rich of an air/fuel mixture engine performance suffers, and ignition misfiring can occur. Too lean of an air/fuel mixture engine damage can occur.
Exhaust gas temperature shows you temperature at which the engine combustion is occurring at. Exhaust gas temperature (EGT) sensor probes are typically placed about 1-2" from cylinder head on exhaust gas manifold runner. Monitoring each cylinder EGTs allows for the ability to "even out" all the cylinders so that all are burning evenly. This greatly increases engine reliability. Monitoring EGTs can also show when detonation occurs, due to the sharp rise in cylinder pressure and drop in exhaust temperature during detonation.
Knock sensors show when detonation is occurring. This is vital in engine reliability and performance. Detonation can melt pistons, tear head gaskets and even ruin rod bearings. Most newer engine management systems allow for individual cylinder knock monitoring, which allows you to pin point the exact moment knock is occurring during engine operation and in what cylinder. These same systems will allow for the knock control to be programmed to detune that individual cylinder so save the engine.
Exhaust back pressure shows the amount of pressure in the exhaust manifold. Exhaust pressure is a critical parameter, as it can give insight into engine efficiency, turbine efficiency, wastegate efficiency and overall engine performance. If a particular exhaust manifold and turbo are not making power, typically backpressure will indicate if the combination is working correctly together. A 1:1 ratio between exhaust pressure and intake pressure is optimal, but is not always achieved. If monitoring backpressure on a log manifold and equal length, you will see a much lower backpressure amount on the equal length manifold which typically indicates an increase in power.
Oil Temperature shows the actual temperature of the oil within the engine. Just like the coolant sensor reporting the coolant temperature, the oil temperature allows for the same information. Oil temperature on a race engine is extremely important, too hot of oil temperature can spell engine failure from lack of cooling or inadequate oiling. If your engine has aluminum rods, the oil has to come up to a normal operating temperature in order for the aluminum rod to expand and hold the proper bearing clearance. Without an oil temp sensor you cannot accurately know if the engine oil is warmed up enough.
The list above only represents a fraction of what can be data logged. Race vehicles that want to know how their tires are doing on track would use infrared temperature sensors to report the tire temperatures during racing, which can be invaluable in selecting the right compound or tire size. A race car wanting to gain understanding of their suspensions performance would use linear potentiometers mounted on the shocks or other suspension parts to measure movement during racing conditions. Knowing the exact distance suspension pieces moved, in conjunction with "g force" can give insight into what needs to be changed in suspension tuning. Lastly, a race car driver may want to know things such as shift force on the shifter, down force on a aerodynamic wing, etc which can be accomplished by a strain gage which measures force. Depending on your application and budget the world of data logging can be exploited to give you all the answers of your driving performance and cars performance, allowing you to improve as a driver and your car to perform at its optimal ability. While purchasing all of the sensors to monitor these parameters can be costly, it's well worth the investment. Its can be the difference of finishing a race, making a key change to win the race or just simply to have piece of mind that your race vehicle is performing properly.
Engine management; the last piece of the puzzle.
So you know that data logging is critical in getting the every last ounce of performance from your race car, as well as monitoring the engine vitals and allowing you to make changes if needed. The last piece of the puzzle is the engine management system itself. Not all engine management system are created equal. The amount of inputs to wire in additional sensors will vary from different manufacturers and models within the same manufacturer. The logging speed and amount of channels that can be logged will vary greatly as well. In order to determine "how much engine management" you require, you need to write down all of your desired inputs that you will log. You will need to include the basic items such as throttle position, manifold air pressure, air temperature, coolant temperature, cam/cranks sensors, vehicle speed sensor and a/f sensor. Then you will need to write down the desired additional sensors for your application. The total amount of sensors will be your "inputs". The total number of inputs is what you need to look at an engine management system spec sheet with. If the system you were budgeting for does not allow for all your desired inputs, you either need to adjust your budget or decide what inputs you absolutely don't need. The next aspect you will need to keep in mind is the logging speed (in hertz) and logging size. You don't want to select an EMS system that you cannot high speed data log very important channels like wheel speeds, engine knock or a system that does not allow you to on board data log for more than 5-10 minutes at a time if your racing will be longer. Just like any electronics the more the systems capabilities the higher the price tag.