Internal Combustion Engine Tuning Mano C. (B11127) IIT Mandi, Mandi Email: [email protected](Name and email of Reviewer: Mahendra Singh Meena [email protected]) Contents Outline 1. Introduction: What is engine tuning? 2. How is engine tuning done? 3. Functioning of the ECU 3.1 Data logging in perspective 4. Engine tuning parameters 4.1 Spark/ignition timing 4.2 Lambda/air-fuel ratio 4.2.1 Throttle body control 4.3 Valve timing and lift 4.4 Boost pressure 5. The caveats 6. Prospects: What does the future hold? 7. References
(Name and email of Reviewer: Mahendra Singh Meena [email protected])
Contents Outline1. Introduction: What is engine tuning?2. How is engine tuning done?3. Functioning of the ECU
3.1 Data logging in perspective4. Engine tuning parameters
4.1 Spark/ignition timing 4.2 Lambda/air-fuel ratio 4.2.1 Throttle body control 4.3 Valve timing and lift 4.4 Boost pressure
5. The caveats6. Prospects: What does the future hold?7. References
1. Introduction: What is engine tuning?
Chip tuning refers to changing or modifying an erasable programmable read only memory (PROM) chip in an automobile's electronic control unit (ECU) to achieve superior performance – this could be more power, cleaner emissions, or better fuel efficiency. Modern engines are equipped with an engine management system (EMS)/Engine Control Unit (ECU) which can be modified to different settings, producing different performance levels. Manufacturers often produce a few engines which are used in a wider range of models and platforms, and this allows them to sell automobiles in various markets with different regulations without having to spend money developing and designing different engines to fit these regulations. Operations like setting the idle speed, fuel/air mixture, fuel flow, spark plug and distributor point gaps, and ignition timing on modern engines are electronically controlled.Engine tuning is typically done after adjustments to the car’s stock configuration - aftermarket camshafts, fuel injectors, supercharger, turbocharger, nitrous, higher compression pistons, ported cylinder head, intake runner, header, and/or exhaust - have been made. Without re-mapping the fuel tables, some of the performance gains from the modifications may not be realized.The larger and more powerful the engine in the first place, then generally the more gains you'll get from remapping. The cost of an ECU remap in India starts at around 70,000 INR and goes up to around 3 lakh INR depending on the capacity of the engine, level of tuning, and remapping brand.
Figure 1: An ICU chip
Even a car getting a relatively low power gain from a remap will actually be livelier to drive. The engine's response under acceleration and its torque curve are the primary reasons for getting into chip tuning.
2. How is engine tuning done?
The most common way to "upgrade" the electronic control unit is using either plug-in modules as mentioned above or using a specialist tuner who will use an On Board Diagnostics (OBD) Flash tool. These devices generally plug into the diagnostic port although in some cases the reprogramming is done directly on the circuit board. Maps are supplied by tuners. Software upgrades will generally be less expensive than either ECU or chip replacement.
i. ECU Flashing: Most new cars are able to be “flashed” through the factory OBD-II scan port. Flash tuning an ECU allows for direct control over all functions similar to a modified stock ECU, but without the need to remove/modify the ECU. Flash tuning is often times the best choice for tuning on newer cars due to being able to retain emissions functionality and cost, reduce time, and provide a one-size-fits-all standard map.
ii. Modified stock ECU: A modified stock ECU is typically one that is EPROM chip based. Using a real time programmer in place of a chip replacement, a custom tune can be performed. A modified stock ECU allows for direct control over all functions of the factory ECU, so excellent performance, fuel economy, and overall running can be achieved.
Another alternative is to have a custom remap for your vehicle. The car/van is connected up to a laptop just like with a standard map, but instead of a one-size- fits-all map being uploaded, the parameters for your individual vehicle can be altered. This is usually combined with runs on a dynamometer, so your vehicle's performance and fuelling all the way through the rev range is checked and tweaked.
3. Functioning of the ECU:
The ECU, the manager of processor-intensive functions, uses closed-loop control, a control scheme that monitors outputs of a system to control the inputs to a system, managing the emissions and fuel economy of the engine (as well as a host of other parameters). With the data it gleans from sensors, it performs millions of calculations each second, including looking up values in tables to decide on the best spark timing and determining how long the fuel injector is open. A modern ECU might contain a 200-MHz processor at its core.
3.1 Data logging in perspective: Data logging is essentially the ability to accumulate values of parameters - such as engine rpm, coolant/air temperature, engine load (PSI), air/fuel, injector duty cycle, throttle position, vehicle speed - related to engine operation. All of these parameters can help you get the maximum performance for a given application, as well as be vital in troubleshooting issues that arise.Data logging can show something as simple as boost leak, being too rich/lean, or not being full throttle. It gives you the ability to compare runs, and make changes to the tune or other settings
based on results. You can achieve much greater results in much shorter time when having as much information as possible on engine/car performance. Some of the sensors used are:
1) Camshaft position sensor: The camshaft sensor determines which cylinder is firing to establish injector synchronization and coil firing sequence.
2) Intake Air Temperature (IAT) sensor: The air charge/manifold temperature sensor is used by the computer to measure air density for fuel mixture control.
3) Lambda (AFR) sensor: It monitors the proportion of oxygen in the exhauststream.
4) Crankshaft speed sensor: It monitors the position or rotational speed of the crankshaft.
5) Coolant temperature sensor: It measures the temperature of the engine coolant.
6) Knock sensor: When a given frequency of knock is detected, it in turn sends a signal back to the ECU warning of detonation, and the ECU retards timing.
7) Throttle position sensor: It sends a voltage signal to the computer indicating throttle angle and speed of movement data.
8) Mass airflow sensor (MAF): It measures the amount of airflow entering the intake manifold using a heated grid or wire.
9) Manifold absolute pressure sensor (MAP): It converts engine vacuum/manifold pressure to an electrical signal so the computer knows how much load the engine is under.
10) Boost pressure sensor: It is a device to control the boost level produced in the intake manifold of a turbocharged or supercharged engine.
The changes in the readings of these sensors manifests itself with the aid of actuators (ignition coils, fuel injectors, cooling fans, etc.) which respond to the ECU’s commands.
4. Engine tuning parameters:
4.1 Spark/ignition timing:
Different timing may result in differing performance. However, to cope with advanced timing, one must run high-octane gasoline to avoid pre-ignition detonation. Manufacturers design for a specific timing and this may limit performance accordingly. Ideally, a spark map is developed on a chassis-loading dynamometer. The car is run on the dynamometer and for every RPM and load, the ignition timing is advanced by tweaking the ECU until torque starts to drop off. The point right before the torque drops off is called MBT or mean best torque. Most engines, especially high-compression and forced-induction types, will encounter knock before reaching MBT. Typically, the low-load ignition timing that the engine uses stock is best. It's really only under high load and with higher-compression pistons, etc. that other areas in the spark map might need to have some ignition advance removed.
IAT sensor: The higher the intake air temperature, the higher the chances of knock. If intake temperatures can be lowered, more ignition-timing advance can be added, which adds power. .
Figure 2: Ignition timing tuning window
Electronic Timing Controllers: The programmable ECU allows us to make changes at any point of the map we encounter knock, leaving the rest alone. With the lower end types, you may have to retard the timing for the whole
RPM map, even though it may only knock at 4500 RPM.
4.2 Lambda/air-fuel ratio:
Most manufacturers tune fuel maps for optimum emissions (running rich to protect the catalytic converter) and fuel economy purposes which can limit performance. This will make the power delivery a lot more linear, which in turn will make the vehicle feel a lot livelier to drive and the engine more flexible.When we remap a vehicle, especially when fuel saving is the priority, we focus on improving the low-end torque in particular and widening the power-band as far as we can. This increase in low end torque will mean less throttle pedal input is required to maintain cruising speeds, when fully laden or when on a gradient. It will also mean that the vehicle will be more comfortable in higher gears at slower speeds as well requiring fewer gear changes overall.One of the most important and basic engine tuning aspects is dialling in the AFR or air-fuel ratio. Unfortunately, 14.7:1 is no magical AFR that will net maximum power. Ideally, an engine should be tuned to have different AFRs under different engine loads and RPM. Rich mixtures control knocking but yield lower fuel efficiency, whereas lean mixtures increase emissions and lead to knocking. For naturally-aspirated cars, AFR's should usually range from 14.7:1 at idle and very light throttle, 14:1 to 13:1 at part throttle, and around 12.5:1 at wide-open throttle. Engines under boost usually are tuned to run rich, which leaves extra fuel in the chamber for cooling and reduces the chances of detonation. On pump gas (91 octane), conservative AFR targets under boost (around 11:1 to 12:1) are used.
Fuel maps: This is a grid with engine speed on one side and engine load on the other.
Figure 3: Air-fuel tuning window
The MAP (or MAF) sensor signal tells us engine load and, based on this and the engine speed, the ECU looks up the two coordinates on the fuel map and injects the correct amount of fuel. Programmable ECUs allow you to change these values and change the AFRs throughout the operating range on the engine.
4.2.1 Throttle body control:The throttle response, the response of the throttle body to stepping on the accelerator pedal, can be varied to provide different driving experiences. These different settings coded into the ECU chip lead to the availability of different driving 'modes', which provide diverse throttle response setting from which to choose. The throttle position sensor comes into play here. Some different modes are: a) Normal mode: This is the default mode of throttle response that comes with the stock engine. It ensures a balance between performance and efficiency. b) Sport/Dynamic mode: In this mode, there is aggressive throttle response (which translates to quicker acceleration) and the gear shift points are remapped into the ECU at higher RPMs for a sporty feel. This means that fuel efficiency takes a hit by letting the engine to rev higher. c) Economy/Eco mode: Here, the gear shift points are moved to lower RPMs keeping in mind fuel consumption and emissions norms. The accessory load in the form of running the air-conditioner is kept a minimum.
Eco-friendly car enthusiasts are obsessed with the Economy mode, whereas those crave the adrenaline rush would swear by the Sport mode.
Figure 4: Different fuel-air ratio modes
The fuel map shown above is equipped with two map sets: a primary and a secondary. These are the two different 'modes' in which the fuel will be supplied differently, and in accordance with the engine RPM and load.
4.3 Valve timing and lift:
Variable valve timing and lift electronic control is necessary to improve the volumetric efficiency of an engine.It provides the engine with multiple cam lobe profiles optimized for both low and high RPM operations. In basic form, the single barring shaft-lock of a conventional engine is replaced with two profiles: one optimized for low-RPM stability and fuel efficiency, and the other designed to maximize high-RPM power output. The switching operation between the two cam lobes is controlled by the ECU which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed and throttle position. Using these inputs, the ECU is programmed to switch from the low lift to the high lift cam lobes when the conditions mean that engine output will be improved. From this point on, the valves open and close according to the high-lift profile, which opens the valve further and for a longer time. The switch-over point is variable, between a minimum and maximum point, and is determined by engine load. The switch-down back from high to low RPM cams is set to occur at a lower engine speed than the switch-up (representing a hysteresis cycle) to avoid a situation in which the engine is asked to operate continuously at or around the switch-over point.
4.4 Boost pressure:
Cars with a turbo fitted can have the requested and allowable boost levels raised, these applications usually have the most effect if the turbo fitted is a low pressure turbo which leaves the most room for improvement.The ECU alters the turbo spool up rates to give maximum power gains. Electronic boost control adds an air control solenoid and/or a stepper motor controlled by an electronic control unit.
Figure 5: Boost tuning window
Wastegate actuators are installed to work in sync with the ECU modifications. The fuel pressure is ramped up earlier in the RPM range but still peak pressure is kept within the factory defined maximum limits, giving a good mid-range power boost and improving the pick-up under acceleration as long as boost pressure is below a predetermined allowable ceiling, the EMS will open the boost control solenoid to allow the turbocharger to create overboost beyond what the wastegate would normally allow. Once desired boost is reached, closed loop based systems react by allowing more air pressure to reach the wastegate actuator to stop the further increase in air pressure so desired boost levels are maintained. This reduces turbocharger lag and lowers boost threshold.
The partial throttle control greatly increases driver control over the engine and vehicle. As overboost reaches the programmable maximum, the EMS begins to decrease the bleed rate through the control solenoid to raise boost pressure as seen at the wastegate actuator diaphragm so the wastegate opens enough to limit boost to the maximum configured level of over-boost.
It is also possible to have a small turbo and large turbo set up with the ECU to use the small turbo at low revs and kick in the larger one as the revs increase.
Variable-geometry turbochargers (VGTs), (also known as Variable Nozzle Turbines or VNTs), are a family of turbochargers, usually designed to allow the effective aspect ratio (A:R) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output.The vanes are optimally controlled by a membrane vacuum actuator, which responds to the actions of the ECU. Turbo lag is also cut down considerably.
Generally speaking, any car will see a benefit from engine tuning, but the largest gains are from turbocharged applications. NA (naturally aspirated) engine power gains are around 10-20% and turbocharged engines have around 30-40% on average.
5. The caveats:
Life is full of compromises. This statement holds for engine tuning, too.
i. A poorly tuned electronic control unit can result in decreased performance, driveability, and may even cause engine damage.
ii. It is very important to use only reputable companies for any sort of vehicle modification in order to prevent serious engine or ECU damage.
iii. Remember that other safety-related items, such as the brakes, suspension and tyres, may also require upgrading. You must also inform your insurance company of any modifications and it is advisable to check, before investing in any kind of engine tuning, how much your premium could be affected. Finally, you should check that any modifications are not invalidating any new or used car warranty.
iv. By chip tuning, you are effectively reducing the safe margin of error the makers build in.
v. Sub-standard fuels, extremes in temperature and altitude, differing emission laws and even the possibility that vehicle may not be serviced on a regular basis and in accordance with the manufacturers recommended instructions.
vi. If a gasoline-powered car is remapped, then there is a need to run the car on premium, high octane fuel – which pushes costs - to avoid engine pre-detonation.
vii. Vehicles with a remapped ECU may be more sensitive to fuel quality and service schedules.
Not all engine makes can be remapped. Some older engines cannot be remapped, whereas car tuning agencies are increasingly looking at new ways to tune those engines which were thought to be not capable of being remapped.
6. Prospects: What does the future hold?
a) It is possible to do away with the camshaft entirely, and to move the valves by hooking them up to electromagnetic actuators. Then, you can trigger the valves individually, and control their timing, simply by feeding power to the electromagnet. Since this is done by controlling electric power, it is quite easy to have the valves actuated by the ECU. In addition, it drastically reduces the number of rubbing moving parts, which increases engine reliability and means that the engine is less likely to suffer a catastrophic failure.
b) Fuel ratio also can be used to regulate or control two fuel types. For example, an engine may have the ability to run on gasoline and ethanol, one being port injected and the other directly injected. Although the implementation of this may require two separate fuel lines and separate fuel tanks, the ratio of the two fuels may be of interest to future ECU programmers.
