About car tuning
Turbo
When planning the choice of a supercharger, the most important criteria are the operating conditions of the car. If the nature of the engine requires extreme toughness and a fast torque curve, properly dimensioned double-slot exhaust manifolds and ball-bearing turbos are a good option.
With these superchargers, the increase in exhaust pressure quickly begins to cut peak power. If you have high peak power in mind, the narrowing of the exhaust manifold and insufficient compression are an obstacle to high power readings. In this case, the supercharger must be increased, which in turn increases turbo lag. Modern car engine rooms are cramped and compromises often have to be made to ensure compatibility. Legal restrictions also present their own challenges when replacing turbochargers on street cars. This is why impeller modifications to the standard supercharger that are invisible from the outside are popular.
Exhaust manifold
In a turbocharged car, the main function of the exhaust manifold is to transfer the kinetic energy of the exhaust gas to the turbo’s turbine blade.
The best exhaust manifold materials for street use and light racing use include ferritic stainless steel materials, such as AISI 441, 309S and 609S. 625 Inconel is best suited for racing use. Normal stainless steel and HST materials are susceptible to fracture at high temperatures and under vibration. Turbo exhaust manifolds are subjected to considerably high thermal loads, not to mention the additional thermal loads introduced by ALS systems used in racing, which also impose challenging conditions on the exhaust manifold material. The working hours play such a large part in exhaust manifold manufacturing that it is not worth skimping on the material. In exhaust manifold manufacturing, it is important to get the pipes parallel to the cylinder channels and to guide the pulse into the exhaust housing as smoothly as possible. It is important to take into account the streamlined position, size and design of any external waste gate channel. In exhaust manifolds produced in China, the quality of the material, the quality of the weld seam and the curvature of the flanges are almost always a problem. Because of these, it comes as no surprise if the exhaust manifold gasket leaks, the weld burr comes off, destroying the turbo, or the weakness of the material leads to the manifold tearing.
Intake manifold/pressure housing
The main function of the intake manifold is to direct air into the engine.
One of the most important tasks of the intake manifold is to ensure that the cylinders are filled as evenly as possible. This is a common problem with many standard intake manifolds, even if the flow is sufficient, there is a risk of damage to one of the cylinders due to a different filling. There are also cases where the flow characteristics are simply not sufficient due to too small channels or valve bodies. A problem with many supercharged engines is also a pressure housing that is too small. Adding a reserve to the pressure housing generally results in a clear increase in peak power. The size of the pressure housing in a supercharged engine must be at least the same size as the cylinder volume and always improves when enlarged up to twice as much. The shape of the pressure housing should be as round as possible, because all sharp corners cause turbulence in the air flowing into the intake manifold. Acceleration funnels, round donuts or the intake manifold channel “runner” are usually installed inside the pressure housing.
Intercooler
There are some cars where the manufacturer has already installed an intercooler that works well enough.
There is no need to replace the intercooler as the first tuning step. However, these are rare, as in most turbo cars the weakness of the intercooler is its small size and poor placement, for example in the inner fender or on top of the engine. The cheapest intercoolers are bar and plate cell models, the disadvantages of which are poor flow capacity, cooling capacity and weight. A better quality cell is fin and tube. The better the cell flows, the less the supercharger has to produce so-called unnecessary pressure, reducing the heat load on both the exhaust and intake sides. The design of the ends of the intercooler is very important in ensuring even air distribution in the intercooler. Smooth and round shapes are a must. In the top cells, sharp metal ramps are made between the pipes so that the air does not collide with the section of cooling fins between the pipes. It is also important to have the cooling stream guided through the radiator, so that all the air coming from the front passes through the radiator. Roughly speaking, five degrees cooler intake air produces one percent more power, and each tight 90-degree bend reduces it by the same amount. Good intercooling can reduce the temperature of the charge air by up to 100 degrees.
Downpipe
The downpipe is the first part of the exhaust system, right after the turbo, and therefore often the first to need replacement when planning tuning measures.
Exhaust gases are at their hottest right after the turbo and therefore need the most space to flow. If the supercharger has an internal wastegate, it is important to take its flow into account when making the downpipe. If the flow of the wastegate constricts the flow of the turbine wheel, it will be visible as a clear dip in the dyno curve when the wastegate opens. If the downpipe is to be enlarged to a size larger than the turbocharger’s turbine blade, it would be a good idea to do it about ten centimeters away from the turbocharger, ensuring the best possible flow. Poor flow on the exhaust side is harmful to a turbocharged car, because temperatures and exhaust pressure increase. Back pressure is poison!
Exhaust system
Many cars’ exhaust systems have poor flow performance due to poor catalytic converters, mufflers, and small pipe sizes.
Often, manufacturers have had to make compromises due to travel comfort and legislation. It is clear that if you change the catalytic converter, the silencers and increase the pipe size, the decibels will increase. However, the sound can be influenced by the pipe size and silencers based on different operating principles, as well as by the design and placement of the pipe end. In a diesel car, sound does not become a problem. In a turbo car, the exhaust system is crucial for the operation of the engine.
Dump/By-pass valve
The conventional dump and by-pass valves are controlled by the vacuum in the intake manifold. The dump valve and by-pass valve are placed in the charge pipe as close as possible to the valve body. When the dump valve releases excess air into the outside air, the by-pass valve directs it through a hose to the intake side of the turbo.
The dump valve reduces the pressure surge to the supercharger during gear changes and engine braking, thus keeping the supercharger speed higher so that the engine responds more quickly to new throttle inputs.
Compression ratio
The biggest differences between turbocharged engines and naturally aspirated engines are the compression ratio.
Naturally aspirated engines usually have a compression ratio of 10-11/1. Turbocharged engines have a compression ratio of 8-9/1. Throughout history, turbocharged racing cars have had high compression ratios due to racing fuels. It is now also possible to increase the compression ratio of a turbocharged engine for street use thanks to ethanol-based fuels (E85). The high compression ratio increases the torque in the low-end range of a turbocharged engine.
Brakes
The standard brakes on many cars are already quite poor for standard power. As wheel grip improves and engine power increases, the demands on the brakes begin to increase considerably.
Standard brakes can be improved slightly with better brake pads, steel braided brake hoses and grooved brake discs, but these cannot do wonders. By increasing the size of the brake disc and brake calipers, braking power can be significantly increased. In street use, it is popular to use larger brakes from a production car (for example, Mitsubishi Evo) or aftermarket brake sets (for example, D2 K-Sport or Wilwood). Brakes are, as the saying goes, the death of speed, but in racing cars these parts are not compromised, so AP-Racing or Alcon are usually chosen as parts.
Motor control
When making mechanical changes to the engine (replacing the turbo, camshafts, exhaust system, etc.), the engine control system must be given new parameters, so to speak.
Most of the engine control units in new cars can be reprogrammed. However, for example, in older cars, programming is not possible or the programming cannot be carried out in the desired way. In that case, you have to resort to retrofit engine controls on the market. When choosing an engine control, you need to define the criteria for what functions are needed. Almost all engine controls achieve the same peak power, but there are also major differences between engine controls in terms of functionality. Installing an engine control unit means rebuilding the computer ECU itself, some of the sensors, and the engine wiring harness. There are also engine controls, ECUs, that go directly in place of the standard ECU, as a companion to the standard wiring harness. An expensive engine control unit is of no use if you do not know how to install and adjust it with iron-clad professionalism.
