#How to tune a diesel or petrol car

24 / March 2022
How to tune a diesel or petrol car

Seletron Performance

How to tune a diesel or petrol car

Here are two of the most popular and classic questions that we are asked that are also searched on Google every single day, namely, "How to tune a Diesel car?" and "How to tune a gasoline car?" Of course, answering this question is not easy, partly because there is no one answer. The factors involved in increasing a car's performance are many, and much depends on the use you are going to make of it, the reliability you want to maintain, the performance you want to achieve, and, of course, also the budget you have.

Let's try to make a macro distinction between the various types of tuning so that we can at least identify some general guidelines and use them to give some more specific indications on the options for intervention. Let's start with the somewhat more extreme car tuning methods and then move on to those that are less invasive, easier to implement, and offer the possibility of immediate restoration to stock conditions.


Complete car tuning: electronic and mechanical

This is a never-ending topic, so we will try to give you some general information; otherwise, we would risk wearing out the computer keyboard without exhausting even half of what is possible to say about car tuning in general. Let's start!


Car tuning by merely replacing the engine with a more powerful one.

We will attempt to discuss only the engine and its accessories and try to avoid introducing other topics (although they may be closely related to engine tuning) concerning car setup and braking system. Let's start by talking about engine performance. Among extreme car tuning, there is the option of merely replacing the engine with a more powerful one. In some cases, the mass-produced engine is disassembled and an engine with larger displacement and power is installed to make things easier and improve reliability.

This may require several adjustments to different parts of the engine's interface with the vehicle, like the engine mounts, then the transmission, the cooling system, and the entire electronic engine management, which may be very different and require a complete ECU replacement. From one point of view, this is a simple and effective elaboration, requiring no special skills in the processing and coupling of the various engine parts but just a lot of work in fitting the new engine into the car. The performance, of course, can be enormously increased, depending on which engine is chosen. A trivial example? Suppose we have a 193hp BMW E39 model 528i and want to have double the power. If we do not want to modify the 6-cylinder inline 24V and turbocharge it entirely, we could directly install the 5-liter V8 from the M5 E39 to immediately have 400 horsepower at our disposal with great reliability!


Car tuning by modifying different engine parts.

Although it often does not require special adjustments in the engine-chassis-transmission coupling, this variety of tuning requires considerable expertise and often requires extremely high budgets, higher than those needed to buy a used engine (in perfect condition) of greater displacement and power. Let's talk about turbodiesel and turbo-petrol engines for a more interesting topic with more margin for increase. At this point, however, we want to point out a couple of general insights that create a huge difference between naturally aspirated engines and turbocharged gasoline engines (on diesel, since there are insurmountable limits in maximum rpm, things are a little bit different, so let's talk about Otto cycle engines).


Power limits in tuning cars with naturally aspirated engines.

In order to simplify the argument as much as possible, the power limit of a gasoline-powered naturally aspirated engine is determined not only by its reliability but also by its engine speed and fuel evaporation rate; we will explain this with an example. Consider a 2-liter 4-cylinder, 16-valve gasoline engine, a classic engine that has a power output of 150hp because it reaches about 6500 rpm. If this engine (by adjusting it mechanically but without varying its displacement) could run at higher revs, it could exceed 200hp (with maximum torque similar to the standard version). This is, for example, what HONDA has done in the past with its V-TEC. If we could run this engine at much higher revs, this 2-liter engine could reach powers of 400 hp, 500 hp, and so on.

Where is the maximum power of this engine limited? As we mentioned above, the first limitation is in the maximum rotational speed that the mechanics of this engine can withstand. The mechanical parts have to be lightened and perfectly balanced to run at 9,000 rpm, 10,000 rpm, and beyond, which is why it is usually the smaller engines that can reach these rotational speeds (see motorcycles) and not the big American V8 engines with large displacements. The other aspect that is a limiting factor is the speed of evaporation and combustion of the fuel, which is why a diesel-powered Diesel engine will never be able to reach high RPMs; the diesel fuel would not have the time to complete its combustion. As you know, standard diesel engines hardly exceed 5000 RPM regardless of their power output, although some exceptions exist, for example, in BMW tri-turbos and some other tuned diesels that can reach as high as 5500 RPM. Returning to naturally aspirated Otto-cycle engines, these can run at very high RPMs if well designed and thus have high maximum power levels.


Power limits in tuning turbocharged cars.


In turbocharged engines, things are very different. We saw before that on a naturally aspirated gasoline engine the maximum torque remains more or less the same because the torque value is given by the amount of fuel that is burned (converted to heat) in each active phase of the engine (burst phase if we are talking about an Otto cycle engine, combustion phase if we are talking about a diesel engine). On a naturally aspirated engine (as the name implies), the amount of fuel that can be injected is dependent on the amount of air introduced: a 2-liter can suck in about 2 liters of air per cycle (actually a little less but let's leave that aside), consequently a certain amount of gasoline or diesel can be injected.

In order to increase the power of a naturally aspirated engine, it is necessary to increase its rotational speed since, don't forget, the power is the product of the torque multiplied by the rotational speed. Since we cannot act (except to a small extent) on the torque, we will have to increase the second value, that is, the speed at which this motive force is delivered (we will discuss how later). On turbocharged engines, things are very different; we are once again talking about an Otto cycle engine since the diesel-fueled diesel engine has the same limitations in rpm even when turbocharged. On a side note, are you wondering why we specify "diesel-powered" when we talk about a diesel engine? It is because the diesel engine can also be fueled with other fuels, even gasoline (it would be damaged after a few moments, but it would change the theoretical considerations we are making).


Back to power limits on turbo-petrol engines.

On this type of engine, two aspects can be effectively acted upon: engine speed and engine torque. Again, we will simplify as much as we can to proceed with the explanation. Things are a little more complex, but in principle we can give this example: let's consider a 2-liter 16V gasoline engine again, this time turbocharged. The naturally aspirated version of this 2-liter with a 4-valve-per-cylinder head will be able to deliver about 200Nm of maximum torque. If it rotates at about 6000 rpm, it will deliver about 150 horsepower, and if it rotates at higher revs, it can exceed 200 maximum horsepower, while its maximum driving force, however, will not be much more than 200Nm.

The same turbocharged 2-liter, if supercharged with a pressure of 1 bar (remember that we are simplifying the concept as much as possible and therefore also the values are indicative if also plausible), will be able to deliver more than 300Nm and, therefore, at the same maximum rotational speed, will have a power output of more than 200 horsepower. The same general consideration applies to a turbodiesel engine, with differences related to the values and the speed of rotation remaining limited. We are still referring to turbo-petrols in this example. Let us leave the maximum rpm unchanged and act on the supercharger value.

If we increase the boost pressure, we can get from the same 2-liter engine a maximum torque of 400Nm with a power output of about 300 horsepower. If we increase the turbo pressure again, we can get 500Nm with a power output of 400 horsepower. Now we also act on the engine speed, and with the same value of turbocharging (and therefore with the same torque value of 500Nm) we increase the maximum engine speed at which this motive force can be delivered and go from the power of 400 horsepower to 500 horsepower.

Increasing the rpm again (same turbo pressure and same maximum torque) brings the power to 600 horsepower. If we further increased the turbo pressure as well, we could have a torque of 600Nm and a power output of 700 horsepower. If we acted on these two parameters again, we could have a 2-liter turbo-petrol engine with 1500 horsepower! Where are the limits? If we leave aside secondary aspects (e.g., the difficulty of creating an engine with very high specific power and adequate delivery in the low to medium rpm range), the limits are imposed by the mechanical strength of the various engine components.

The high engine speed makes it important that every moving part of the engine be perfectly balanced and strong. Furthermore, even the simple valve-closing action (implemented by springs) can become a problem (have you ever heard the term desmodromic?). The fact that this is then a supercharged engine makes the whole connecting rod-crank system subject to great mechanical stress, which is why the sizing of the various components is crucial in ensuring that the engine does not explode at the first acceleration (this is not a figure of speech, the engine can literally open up due to failure of the bolts holding the head, cylinder block, and crankshaft supports together).

High boost pressures generate very high-pressure peaks during compression and combustion, and everything also affects the thermal aspects of the engine. For this reason, it is complex to achieve high specific power values while maintaining good reliability. Do you want to know which 2-liter turbo-fuel series engine (at the time of writing) has the highest specific power in the world? The answer is the Mercedes engine used in the A43 AMG, the only mass-produced turbocharged 4-cylinder engine capable of delivering 500Nm of maximum torque with a maximum output of 421 horsepower (with a boost pressure of around 2 bar); this is a specific power output of more than 210hp/liter. Already this specific power required remarkable mechanical and electronic technical solutions to ensure excellent reliability.


Power limits on turbodiesel engines.

On turbodiesels, the considerations are similar to those made for turbo-petrol engines, with the difference being that the Diesel engine cannot go much higher than the maximum rpm, which has a value of around 5000 rpm. It goes without saying that to increase the power of a turbodiesel, you will not be able to act more on the rpm, but you will have to act exclusively on the engine torque value and, therefore, on the supercharging values. In order to be able to inject a high amount of diesel and burn it properly, high turbo pressures are needed. On turbodiesel engines, the limits are exclusively mechanical in origin; in fact, there are no particular problems related to the maximum speed of the components in a reciprocating motion (pistons, connecting rods, valves) precisely because of the maximum rotational speed, which will still be less than 6000 rpm.

On the other hand, there are robustness requirements related to the need to handle high boost pressures, hence the sizing of pistons (also very thermally stressed in the piston crown itself, which indirect injection engines, thus all common-rails, represent the combustion chamber), connecting rods, crankshaft, crankshaft bearings, connecting rod supports, and plugs. Let us also not forget the need to create reliable elements in the device that generate the boost pressure, namely the turbocharger. This fine device, composed of several components, rotates at very high speeds (as high as 200,000 rpm) and must withstand the temperatures coming from the exhaust gases hitting its turbine.


How to tune an aspirated gasoline car.

In order to increase the power output of a car with a gasoline aspirated engine, as we have seen, one must mainly work on the engine speed. The most important elements to be adjusted are pistons and connecting rods, camshafts, intake manifolds, exhaust manifolds, intake box and air filter, exhaust system, and the electronic management. When the engine speeds are raised significantly, work must also be done on valves and valve springs. In principle, it is possible to significantly increase the maximum power output of a gasoline aspirated engine, but this generally results in a deterioration of the delivery in the low and mid-range revs. In addition, the cost required to work on all these aspects can be very high.


How to mechanically tune a car with a turbodiesel engine.

To increase the performance of a car with a turbocharged diesel engine, the amount of injected diesel fuel and the boost pressure must be altered. In fact, in order to burn all the injected diesel fuel, a large amount of oxygen-rich air is required. This air comes from the turbocharging system, i.e., the turbocharger (or turbochargers if it is a multi-stage turbocharging like on the BMW 123d, 335d, 550d, or other Mercedes, AUDI engines, etc.).

Classic (but expensive and invasive) tuning consists of replacing a turbocharger with one of a larger size that is capable of working with higher pressures, replacing the intercooler (which is used to lower the temperature of the compressed air to make it denser and, therefore more oxygen-laden), replacing the exhaust system (also with possible de-fap and de-cat), replacing the air filter and the consequent reworking of the electronic management by complete remapping of the memory contained within the ECU. This group of modifications can lead to high increases in power and torque, even doubling maximum power. However, they are very expensive and complex interventions that make the car difficult to restore and to standard condition and which will be very costly to undo.


How to electronically tune a car with a turbodiesel or turbo-petrol engine.

Modern turbodiesels (and this also applies to engines produced after the second half of the 1990s) can also be tuned with excellent results by working on the electronic management alone, thus without replacing mechanical parts of the engine. There are basically two methods for electronic tuning (or a mix of these in some cases).

Through remapping the ECU: we have talked about it other times as well; from a technical point of view, it is a valid solution. It allows excellent power gains and has an affordable cost (be wary of those who offer cheap remappings). The main problem with this tuning is that it can leave indelible traces on the ECU, a problem, for example, for the manufacturer's warranty, which lapses the moment ECU tampering is detected.

Another risk is related to the unprofessionalism associated with some preparers who remap car ECUs without the necessary in-depth technical knowledge and can cause serious engine damage. The second method of electronic tuning, the one we have been doing for more than 20 years, consists of installing an additional chip tuning unit that works together with the ECU without taking any engine safety controls away from it.

This is an affordable solution that leads to excellent increases in power and torque and has the great advantage that it can be mounted and dismounted easily without leaving evidence. Another important advantage is that it can be adjusted according to the driver's needs and can be switched on and off at any time. The most complete version, the CHIPBOX CONNECT, even allows you to manage the output of your engine from your Smartphone!

In recent years, since standard engine control units are inviolable or otherwise keep track of any external reprogramming (even if done via OBD). SELETRON digital chip tuning modules have become a preferred choice for several reasons. First and foremost, the ease of installation. All kits for common-rail diesel and turbo-petrol engines come complete with top-quality wiring harnesses that already incorporate connectors identical to the original connectors mounted on the engine harness. Installation is very easy and within reach of anyone who likes D-I-Ying it.

Also, crucially, we repeat that the installation of our add-on ECUs does not require any irreversible modifications or tampering. No need to modify any mechanical parts, no need to open or reprogram your car's ECU, and no need to cut or solder wires. Just hook up the original connectors found in each kit, and the add-on chip tuning unit is ready to work and increase your engine's power and torque values. The increased torque availability at low revs also allows you to be able to optimize gasoline or diesel fuel consumption. This type of processing is the most popular because it allows almost anyone to install the ECU themselves and be able to remove it if necessary.

Some car tuners also use our additional ECUs on cars that have already been mechanically tuned and on which an ECU remapping has been carried out (via OBD or via BDM). This is done in order to implement an additional increase in power and to be able to manage this additional performance via their smartphone. This type of electronic tuning with external digital electronic module assembly is available for all turbodiesel engines and all turbo-petrol engines.

The achievable power increases are about +30%. Browse through our online shop of chip tuners, and you can find your model and see the specific power increase values (in horsepower) and the maximum torque increase value (expressed in Nm). You can also see if the Smartphone manageable version is also available for your car, whether the accelerator pedal chip tuning additional module is available, and where applicable, the chip tuning unit that manages the valves that control the sound in the exhaust system of some sports cars.


If you want to process your car, consider our upgrade kits. They are made in Italy, covered by an official SELETRON warranty, are TUV Austria certified, and are used in various countries worldwide for non-invasive electronic tuning of cars of the most prestigious brands! Search the catalog for your model and see what we can offer you to increase your car's power and torque! You will receive at home a kit complete with everything you need for a clean and safe do-it-yourself installation, complete instructions with photos of your car's engine, and you can always count on our assistance in case of doubts or difficulties.

If you like these technical topics, come back and read us; you will always find interesting and insightful information!


You might be interested in:

How our add-on chip tuners for Diesel engines with VP37 electronic rotary pumps work >>> Read Now

How our add-on chip tuners for engines with VP44 radial piston injection pumps work >>> Read Now

How our add-on chip tuning units for common rail engines work >>> Read Now

How our chip tuning modules for injector-pump engines work >>> Read Now