Tietoa auton virittämisestä
One of the most important criteria for choosing a turbo charger are the conditions where you will use your car. For utmost tenacity and rapid torque response, carefully dimensioned dual exhaust chambers and ball-bearing turbos are the correct choice. The drawback is quick flattening of the exhaust pressure curve , which is not ideal for those seeking peak power, as the size of the exhaust chambers and insufficient compressor volume limit top end power. For max peak power, a bigger turbo is needed, but this increases lag.
Engine bays in modern cars are cramped and require compromises to meet end-user expectations. For street-legal cars legislation often limits the size of turbos. This is why internal mods to factory-assembled turbos, such as increasing the compressor and turbine wheels, are popular as they are not so visible.
In turbo-charged cars, the exhaust manifold’s main function is to transmit exhaust flow kinetic energy to the turbine wheel. Ferrite RST compositions, such as aisi 409 and 609, are most suitable fabrication materials. Basic RST and HST based materials have a tendency to crack under vibration and high temperatures. Exhaust manifolds of turbocharged engines need to resist very high temperatures, even more so with ALS systems frequently used in race engines. When building a customized exhaust manifold, the amount of work outweighs easily material costs, so we recommend to use best available materials for an optimized and long-lasting result.
When fabricating a customized exhaust manifold, it is important to align the pipes with the cylinder chambers in order to smoothly channel the exhaust drift into the manifold. For an external waste gate equally important is to consider the size, shape and chamber alignment for a dynamic flow. In low-priced Chinese exhaust manifolds the quality of the build materials, welding seams and wonky flanges often cause problems, so don’t be surprised to witness manifold cracks and gasket leaks, even residual welding particles ending up destroying the turbo charger.
The main function of the intake manifold is to induce air into the engine. One of the most important tasks is to perform forced induction in the most uniform manner to all cylinders, which is challenging among stock manifolds; despite sufficient air volume, the danger lies in non-uniform cylinder air fill resulting in imbalanced combustion and cylinder damage. In some cases even the air volume is insufficient due to undersized manifold conduits or throttle body. Another typical problem is an undersized pressure chamber or plenum, an intricate part of the intake manifold. Additional peak power can be achieved by adding reserve to the plenum, which should equal the volume of engine displacement, and for urther gains are achievable by up to doubling it respectively. The shape should be as round as possible to eliminate sharp corners causing unnecessary turbulence. Acceleration cones or “donut”s are often installed inside the pressure chamber, or the chamber runner is rounded to optmise air flow.
Some cars come pre-assembled with a sufficient intercooler already from the factory, eliminating the need for replacement as a first tuning measure. This, however, is more of an exception as most factory-assembled intercoolers are undersized and placed non-optimally, e.g. side-mounted behind the fender (SMIC) or on top of the engine (TMIC). Economy intercoolers are typically type “bar&plate” characterized by insufficient air flow, cooling capability and hefty weight. A much better option is “fin&tube”. The better the flow in the intercooler core, the less the need for so called “excess pressure” needed from the turbo charger, hereby reducing heat load from both intake and exhaust stages. The design of the intercooler’s lateral edges plays an important role in ensuring uniform air distribution; softly rounded shapes are usually needed. Top-engineered intercoolers have sharp metal sheet ramps to restrict air colliding directly to the cooling fins, thus maximising heat rejection. Of importance is getting the air draft to flow to the intercooler in order to benefit from the air entering the front grille. As a rule of thumb, every 5 degrees of decreased air intake temp produces 1% power increase, and every sharp 90 degree angle accounts for the same amount of power loss. A well engineered intercooler can reduce compression air temperature up to 100 degrees
The turbocharger is followed immediately by the downpipe, which is first in line for a change when tuning a car. Exhaust gases are at their hottest right after the turbocharger thus requiring the most volume in order to flow properly. When designing the exhaust flow in a downpipe, special attention is needed with chargers equipped with an internal wastegate. A clear drop in the dyno curve can be seen when an opening wastegate restricts the flow in the turbine wheel. If the downpipe is designed larger than the turbine wheel, it should be located at 10 cm apart from the charger to ensure optimum flow. Insufficient flow causes temperature and pressure increase at the exhaust stage, resulting in backpressure, which is very harmful for turbocharged cars.
The flow in the exhaust pipes of most cars is inadequate due to badly designed catalytic converters, mufflers and insufficient pipe diameters. Compromises are made due to legislation and for passenger comfort . Increasing the exhaust pipe diameter and replacing cats and mufflers with larger ones inevitably reflects in noise levels. By paying attention to exhaust pipe sizing, muffler technology as well as the shape and placement of the exhaust tips, noise levels can be reduced. While not so much of an issue in diesel engines, the design of the exhaust pipe system in turbocharged combustion engines should not be undermined.
A dump-valve decreases the pressure wave shock to the turbocharger when shifting gears and during motor braking by maintaining a higher spooling rate in the turbo resulting in faster throttle response. Traditional dump and by-pass valves are controlled by underpressure from the intake manifold, and are placed in the induction pipes close to the throttle body. While a dump valve releases the extra air into the atmosphere, a by-pass valve redirects it back through a hose to the turbo’s induction stage.
Compression ratio is one of the biggest difference between turbocharged and naturally aspirated Otto-engines. The compression ratio of the latter is within 10-11:1 equivalent to 10-11 kg per 1 kg of fuel, while for turbocharged engines it is 8-9:1. Turbo charged race engine compression ratios have traditionally been higher thanks to race fuels. Nowadays it is also possible to increase the compression ratio of turbocharged street-engines thanks to ethanol-based fuels (E85), which improves low band torque.
Factory-mounted brakes are mostly insufficient even for stock powered engines. Better tire grip and increased engine power set even higher demands for brakes. Stock brakes can somewhat be improved by replacing brake pads and pulling steel-braided lines and mounting grooved discs. Major improvements are achieved by increasing disc size and upgrading the calipers. Popular among street cars is to fit bigger brakes from other import cars (e.g. Mitsubishi Evo) or use after-market brake kits (e.g. D2 K-Sport and Wilwood). As the saying goes “Brakes are the sum of speed”, thus selecting brakes for race cars is non-negotiable, and so the option is either AP-Racing or Alcon.
When doing mechanical changes to an engine (e.g. turbocharger, cams, exhaust etc.), the engine management also needs new parameterisation.
Most car manufacturers’ engine managements systems cannot be re-programmed. The alternative is an after-market engine managements system. Criteria for choosing one depends on the required level of functionality . Most aftermarket EMS’s achieve more or less the same peak power, but their functionality varies a great deal. Installing a new EMS requires re-building the computer ECU, sensors and a completely new harness, although bolt-on systems are also available. But even an expensive aftermarket EMS becomes useless, unless it is assembled and calibrated professionally.