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14-XI-2014
HELP CENTER (D4B + D4T)

2. Engine tuning

2.1 Main menu

Screen Shot: DIAG4TUNE Main Menu  
DIAG4TUNE Main Menu  

2.2 Reasons for tuning (in relation to H-D engine)

  • Motorcycle design – Customizing the motorcycle to meet the individuals design
    • Changes to engine intake system
    • Changes to exhaust components
  • Making sound of the V-Twin engine more distinctive
  • Increasing engine performance (preferring an increase in torque at medium RPM of the engine rather than racing for maximum performance nearing the RPM limits)

2.3 Tuning for mechanical modifications

  • Installation of a new engine intake system which is usually accompanied by the installation of a high flow air filter
  • Mounting of new exhaust components or the whole exhaust system. Additionally, in the case of an "open exhaust", there may be an alternative with additional installation of a baffle for long trips
  • Modifications to the combustion chambers keeping the same or increasing the compression ratio
  • Modifications to the distribution system (changes of dimensions and timing of valves and/or accelerating the valve function, i.e. replacing the cam)

2.4 Positive results of tuning by mechanical modifications

  • Owner has an individualised motorcycle
  • The sound of the engine is tuned to the requirements of the ownerThe engine maintains stable running in all cruising modes
  • The engine accelerates smoothly and steadily from low RPM modes
  • The increase in engine performance parameters can be sensed when accelerating (even partially) and there is a need for a stronger grip of the handlebars and evidently quickly diminishing objects in the mirror

2.5 Possible negative consequences of tuning with mechanical modifications

  • The engine runs rough in some cruising modes (e.g. urban cruising at 30-50 km/h, 20-30 mph), and it is difficult to find the optimal gear to suppress an occasional and annoying miss of the engine ignition
  • The engine lags under hard acceleration
  • The actual performance is less than what was promised by the tuning parts supplier
  • Engine backfires during decelerations

2.5.1 Causes of negative behaviour of the engine

In most cases, components of the intake and exhaust have been installed which have a greater flow of air or exhaust gases than the original components. As a result, the engine is able to take in a larger amount of air compared to the original condition. This means that you have managed to increase VE - Volumetric Efficiency of the engine expressed in %. Simply said, VE value is expressed by the following relationship:

 VE = (amount of the actually air taken in) / (engine displacement) %

VE values are arranged in a map (table), they are stored in the electronic control module of EFI, and represent volumetric efficiency of the engine over the entire range of the engine function. There are two types of VE maps; generally, the most widespread VE map is organised as the dependency of VE on the engine speed (RPM) and the angle of the throttle opening (TPS throttle position sensor). New types of injection systems use a map arranged as dependency of VE on the engine RPM and the absolute pressure in the intake manifold (after the throttle) (MAP = manifold absolute pressure), and it is expressed in kPa. The important fact is that each cylinder has its own VE map. Each cylinder has a different pattern of VE, particularly due to the V-twin cylinder arrangement.

By installing new intake or exhaust components, or both of these, we have managed in certain modes to increase the VE values, then we have quite clearly created conditions for increasing the torque of the engine in these modes by the same percentage.

For a tuning centre which modifies the construction of exhaust pipe(s) and intake systems, a VE map is key, for evaluating the results of tuning. This means that the biggest advantage of a VE map as a measure of successful tuning is that it describes the global pattern of the torque characteristics of each cylinder of the engine in all RPM and performance modes. In contrast, when measuring performance parameters of an engine at any test bench, you can only obtain performance data for the entire engine. In most cases, this is only what we call external performance characteristics. These characteristics are measured only at full throttle, a mode rarely used in normal operation. Furthermore, this measure is loaded with measurement errors exceeding 5% of the measured values.


2.6 Fuel maps - summary of the important facts

VE maps for each cylinder are the basis of the fuel maps. These show the ability of the engine to take in air. When we have mounted new components (intake system, exhaust pipe, etc.), it means a significant modification to VE maps. The fundamental problem is that the electronic control module of the EFI does not know about it yet and it still controls the mixing air-fuel ratio (AFR - see wikipedia) for the engine in the same way as before with the original components (intake, exhaust, etc.) 

AFR value is expressed by the following equation (the amount of air and fuel is expressed in kg): AFR = amount of intake air / amount of fuel injected

This brings us to another part of the fuel map, which is the AFR map. It defines target AFR values in the control module. This is only one common map for both cylinders and is defined as the dependence of the target AFR on engine speed (RPM) and the absolute pressure in the intake manifold (after the throttle valve, MAP - manifold absolute pressure)

In total therefore, there are 3 fuel maps of H-D engines:

  • VE MAP of the front cylinder - VE FRONT
  • VE MAP of the rear cylinder - VE REAR
  • Map of target AFR - AFR

Based on these three maps, the EFI calculates the amount of injected fuel in all modes. The amount of fuel is determined by the basic parameters of the injector, i.e. the fuel flow per unit of time and the time of injection which is controlled by the EFI system. There is one important exception, which is applied when the value is set at 14.6 in the AFR map. If the engine ranges within the modes where the target value in the AFR map is set to 14.6 and the injection system is equipped with a narrow-band lambda sensor, it immediately begins to work in a closed loop.

2.6.1  VE MAP of the front cylinder - VE FRONT

Screen Shot: VE Map of the front cylinder – VE FRONT (table) Screen Shot: VE Map of the front cylinder – VE FRONT (graph)
VE Map of the front cylinder (table) VE Map of the front cylinder (graph)

2.6.2  VE Map of the rear cylinder - VE REAR

Screen Shot: VE Map of the rear cylinder – VE REAR (table) Screen Shot: VE Map of the rear cylinder – VE REAR (graph)
VE Map of the rear cylinder (table) VE Map of the rear cylinder (graph)

2.6.3  MAP of target AFR - AFR

Screen Shot: MAP of target AFR - AFR (table) Screen Shot: MAP of target AFR - AFR (graph)
Map of the target AFR – AFR (table) Map of the target AFR – AFR (graph)

Based on these three maps, the EFI calculates the amount of injected fuel in all modes. The amount of fuel is determined by the basic parameters of the injector, i.e. the fuel flow per unit of time and the time of injection which is controlled by the EFI system. There is one important exception, which is applied when the value is set at 14.6 in the AFR map. If the engine ranges within the modes where the target value in the AFR map is set to 14.6 and the injection system is equipped with a narrow-band lambda sensor, it immediately begins to work in a closed loop.


2.7 What is a narrow band lambda sensor and stoichiometric Air-Fuel Ratio (AFR)

A lambda sensor can very accurately evaluate the stoichiometric air-fuel ratio (AFR) which is currently 14.6 (sometimes referred to as 14.7) kg of air per 1 kg of fuel. In theory, this is the ratio which should result in complete combustion and therefore the most economical fuel efficiency with minimal amount of harmful combustion gas.

It can be expressed by a simple chemical equation:
14.6 kg of air (21% O2 + 79% N2) + 1 kg of petrol (CxHx) => (H2O + CO2 + N2)

Note:
The stoichiometric ratio of 14.6 (or 14.7) is obviously dependent on the chemical composition of the petrol fuel which is a mixture of defined classes of different hydrocarbons. The value specified represents the conventionally determined average value for the standard petrol fuel.

Therefore, if you burn gasoline fuel with the correct amount of air (hence oxygen, because in theory nitrogen, as an inert gas, does not enter the reaction), the result of combustion is only water, carbon dioxide that we drink in beer and soda, and inert nitrogen. Carbon dioxide is "food for plants which, through photosynthesis acquire carbon from it, which is important for the construction of the plant body, and they release oxygen back into the atmosphere".

In fact, CO2 has been branded the main culprit of global warming by the "green terrorists" who managed to assert its control as a pollutant for internal combustion engines as well. It is partly a paradox because maximum CO2 emissions of engines represent their optimal settings in the stoichiometric ratio - AFR. The only way to achieve these restrictions is "downsizing" of engines, i.e. reducing the displacement of the engine trying to compensate this by increasing its efficiency. In Harley-Davidson engines this would entail reducing displacement of the engines every year, a trend already evident in cars. Bright prospects.


2.8 Injection system operating in a closed loop

If the Fuel Injection system operates in a closed loop, it means that the fuel map is taken as a default for the calculation of the amount of fuel controlled by the time of fuel injection, then the calculation is corrected by the information from the lambda sensor for each cylinder to achieve AFR of 14.6. Seemingly, it should be sufficient just to use a closed loop across the entire engine operation range to compensate for the modification of the intake and exhaust systems, and the engine should automatically use the newly acquired better engine filling without further modification. True, but only to a very limited extent; for two reasons:

  1. The control system of the lambda sensor is restricted to a limited operating range around the stored fuel maps, which is logical. The task of the control system is also to indicate any failures of the fuel preparation if they exceed the permitted tolerance. If this does happen, the system will start working in an emergency mode which will try to keep the engine running to finish the journey, and limitations can be expected in higher values of MAP, i.e. in the area of higher engine load areas.
  2. Although controlled combustion with AFR of 14.6 is optimal in terms of fuel consumption and harmful engine emissions, it is not an optimal value for maximum torque which requires the AFR to be at 13.5 (i.e. with an excess of fuel). Even richer mixtures are used in the area of maximum performance parameters, down to about 12.5 AFR. Excess of fuel works as a coolant which protects the combustion chamber and its components from overheating. In this case, latent heat of excess fuel is used to remove excess heat from the combustion chamber during the conversion from liquid to gaseous states.

2.9 How to tackle the negative effects of tuning through mechanical modification

Ironically, after installing performance-boosting components – intake and/or exhaust components – one often ends up with less performance than before the changes. It is often caused more by our wish than the reality; the bike sounds better but there are now some inconsistencies in some modes of the cruising range. Often warnings in the installation instructions of a new intake or exhaust components are underestimated, as they do recommend optimising fuel maps.

So, there are 3 options to address the problem:

  1. Get used to the flaws of the engine - then there is no point in reading further
  2. Reinstall the original intake or exhaust components - again, there is no point in reading the further text
  3. Reconfigure the fuel maps for your bike - then continue to tuning