Engine tuning

Tuning diagrams of a BMW F 800 GS : blue curve BMW factory control, green and red curves alternative regulations for engine fine-tuning. The three diagrams recorded for the engine speed : above power in HP , middle torque in Nm , below air-gasoline mixture ratio . The tuning achieved a slightly higher performance (max. 13%) and a cleaner and more efficient combustion process through better control of the mixture ratio.

The term engine tuning describes, typically subsequent, performance or efficiency-enhancing measures on internal combustion engines that were not carried out by the manufacturer . This tuning measures are the usual engine metrics such as PS / kW or torque over the speed characterized. The English term tuning actually means (fine) tuning.

history

In the 1970s, tuning engines could almost be described as a popular sport , and a lot of the work was done on one's own at home. In the course of time, however, companies and well-known car manufacturers discovered this lucrative business. So has z. B. Mercedes bought the AMG company from the three largest competing car tuners of Mercedes models AMG , Brabus and Lorinser . Today, it manufactures tuned Mercedes vehicles under the Mercedes-AMG brand .

Principles

In the theory of engine development, the topic of increasing the performance of an existing machine is examined exclusively from the following three perspectives:

Increase in the mean pressure

The mean effective pressure is the work done by the engine in one work cycle, based on the displacement. Increasing the mean effective pressure increases the torque. All measures except the increase in displacement and the increase in engine speed serve to increase the mean pressure. This means that the combustion pressure must be increased and the pressure losses due to the charge change (intake, expulsion of the combustion gases) must be reduced. Typical measures for naturally aspirated engines are to increase the compression and for turbo engines to increase the boost pressure.

Increase in stroke volume

The increase in displacement increases the mass throughput and thus the amount of fuel that can be chemically converted per work cycle. The maximum possible amount of air is thus increased, this is done by drilling out the cylinders or making changes to the crankshaft (increase in stroke). Due to the comparatively high costs, this tuning variant has become very rare in modern engines.

Increase in speed

When considering the performance formula , an increase in speed can also be achieved by increasing the speed . If the pending torque is increased at the rated speed, the power also increases, as can be seen from the formula. An increase in speed alone does not allow an increase in performance if no other adjustments have been made (example: remove the speed limiter). The maximum speed is limited by flow losses, the time required for mixture formation and the maximum piston speed . A good example was the Audi RS6 Plus, in which the boost pressure was kept at its maximum for longer and received an increase in output of 30 hp with the same mean pressure / torque, displacement and maximum possible speed.

Motor power formula

${\displaystyle P=M\cdot \omega ={\frac {M\cdot \pi \cdot n}{30000}}}$

${\displaystyle P}$ = Motor power in kW

${\displaystyle \omega }$ = Angular velocity

${\displaystyle M}$ = Torque in Nm

${\displaystyle n}$ = Nominal speed (engine speed) in 1 / min

or ${\displaystyle P={\frac {p\cdot A\cdot s\cdot z\cdot n}{t\cdot 300}}}$

${\displaystyle p}$ = mean effective working pressure in bar

${\displaystyle A}$ = Piston area in dm²

${\displaystyle s}$ = Stroke in dm

${\displaystyle t}$ = Revolutions per cycle (1 for two-stroke engines, 2 for four-stroke engines)

${\displaystyle z}$ = Number of cylinders

This formula clarifies the procedures addressed under principles:

Increase in mean pressure (p)

Increase in stroke volume (A × s × z)

Increase in the nominal speed (n)

1  HP corresponds to 735.49875 W. In order to convert kW into HP, the number of kilowatts must therefore be divided by 0.73549875 or multiplied by 1.3596216173.

discussion

Since a series engine often represents a balanced compromise in terms of efficiency, environmental compatibility and service life, it should not be changed lightly. However, there are certainly applications in which tuning the factory compromise solution in a more specialized direction (higher performance, higher efficiency, etc.) can be useful. Renewed (fine) tuning can also achieve a better tuning of an engine than the original factory tuning by the manufacturer of an engine at the beginning of its life. However, if you want to safely rule out a potential legal conflict, it can be recommended as an alternative to increasing performance through tuning to choose the next stronger variant of the corresponding series vehicle.