#Chip tuning for naturally aspirated engines

08 / March 2022
Chip tuning for naturally aspirated engines

Seletron Performance

Chip tuning additional units for naturally aspirated gasoline engines and why we don't supply them.

For those unfamiliar with the term, aspirated gasoline engines are engines that draw air by suction independently due to the depression created in the cylinders during the intake phase. In this context, we will discuss 4-stroke gasoline engines. These engines are thus named because the engine makes four strokes: intake, compression, combustion, and exhaust. In the first phase, the intake phase, the piston moves from the TDC (top dead center) to the BDC (bottom dead center). In this phase, the exhaust valve is closed and the intake valve, connected to the intake manifolds downwind of the air filter, is fully open. Due to the vacuum created during the descent of the piston, air is sucked in from outside (atmospheric pressure) until the cylinder is (almost) full. This is where the name naturally aspirated engine comes from, which applies to Otto cycle engines (gasoline engines), Diesel engines, and LPG or Natural Gas engines.

The opposites of naturally aspirated engines are supercharged engines, i.e., turbocharged engines, those with a volumetric compressor, and the lesser-known supercharged engines by Comprex ( a practically unused technology). To be precise, we must also talk about the recent turbodiesels with two-stage supercharging. In rare cases, an electro-compressor generates some supercharge using a turbocharger and a centrifugal compressor driven by an electric motor. Let's return to the topic at hand or to our naturally aspirated gasoline engines and why we do not provide additional control units for this category of engines.


Gasoline aspirated engines before the advent of electronics.

Several decades ago, gasoline engines were powered by the carburetor, a device generally centralized (one carburetor per cylinder) that prepares the mixture of air and gasoline in a completely mechanical and inaccurate way. Today no more gasoline engines are produced with carburetors due to several issues related to emissions and efficiency. In the past, gasoline engines were almost exclusively fed by single carburetors, twin-body carburetors, or multiple carburetors (one carburetor per cylinder, a performance solution but complex to set up), if we exclude the few engines with mechanical gasoline injection used, for example, on some Audis and Bentleys, among others.


Aspirated gasoline engines after the advent of electronics.

At the turn of the '80s and '90s, gasoline engines began to use two electronic injection systems, the SPI and MPI, or the Single Point Injection and Multi-Point Injection Systems. The first used a single injector instead of the carburetor, a configuration that electronically controls carburetion even if the performance is not optimal. This solution is used only on non-sport engines. The second solution, widely used even today, provides one injector per cylinder. It is an indirect injection system (like the SPI system), but it allows a much more precise preparation of the mixture, providing better efficiency.


Indirect gasoline injection systems require the maintenance of the stoichiometric ratio, i.e., a precise mass ratio between the amount of air intake and the amount of gasoline injected. This ratio is 14.7:1, where 1 is the mass of gasoline and 14.7 is the mass of air introduced into the cylinders. Two systems are used to stabilize the ratio: the first is the reading of the mass of air intake through the MAF (Mass Airflow Meter), and the second is a feedback system consisting of a sensor mounted after the engine exhaust (the lambda sensor) that detects the amount of residual oxygen after combustion.

The electronic engine management ECUs manage the electro-injectors, calculating the quantity of gasoline to be injected into the cylinders according to the engine load, the rotation speed, the air intake mass value, the lambda value, the engine temperature, and the air intake temperature. The multi-point injection system is schematically similar to a common-rail diesel system: pressurized gasoline (about 3 to 5 bars depending on the type of system) is stored in a "rail" to which all the electro-injectors are connected and controlled by the injection unit. The preparation of the mixture takes place in the section that goes from the intake manifold near the injector to the cylinder inlet.


Aspirated engines with direct petrol injection

More and more manufacturers have started to produce gasoline engines with direct injection over the past decades, for example, Mitsubishi with its GDI. The system is similar to indirect injection, but the gasoline pressure is much higher (100-200 bar), and the injectors, like Diesel engines, are placed on the engine head. The gasoline is injected directly into the combustion chamber created between the engine head and the piston crown. This injection system has many advantages: the fluid-dynamic yield of the intake manifolds is higher, and it is possible to create stratified charge injections bypassing the stoichiometric ratio. In practice, the injector atomizes a small amount of gasoline in a non-uniform and concentrated way in an area that is "lit" by the spark plug; the rest of the combustion can occur where the percentage of gasoline is lower (thinning of the air-fuel mixture).

Therefore, direct petrol injection engines can work with leaner mixtures under certain operating conditions (generally low engine load), thus reducing petrol consumption. As the load increases, the air-fuel ratio returns to values similar to those of indirect injection engines. Another advantage is the accuracy of the injection and the performance of the engine. Additionally, an engine with direct petrol injection is easier to start when hot because it is less subject to variations in the preparation of the mixture that occurs in engines with indirect injection and more so in carburetor engines.


Electronic tuning of an aspirated gasoline engine.

Given what has just been said, and even more so for indirect injection gasoline engines, it is clear that the amount of gasoline that can be injected is closely related to the amount of air intake. Not being able to change the amount of air introduced into the cylinders (due to the lack of a compressor that generates supercharging), the increases in power and torque obtainable on an aspirated gasoline engine by only modifying (greasing) the preparation of the mixture, are extremely low. In short, the increase in power and torque, depending on the engine, could be around 2 - 4%, almost imperceptible values in terms of real performance.

Our company has always searched for high-tech solutions with maximum reliability while also striving for maximum effects in terms of performance and increased driving pleasure. Although it is perfectly possible for us to manage the electronics that govern the operation of aspirated gasoline engines, we have decided not to provide additional chip tuning units for this type of engine in order to maintain our high standards in terms of power increase, torque increase, general increase in performance and driving involvement. This is the answer to the initial question, "why don't we provide you with additional chip tuning units for naturally aspirated gasoline engines."

The discourse regarding supercharged gasoline engines is different, whether they have an indirect injection system or the more advanced direct injection gasoline engine, but we will talk about these and how we are able to process them in a future article. We advise you to keep an eye out and read that article precisely because we will talk about great increase in performance, excellent reliability, and ease of installation you get with these engine tuners!


Until the next article!


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