Modern engines are equipped with an engine management system which can be modified to different settings, producing different performance levels. Manufacturers often produce a few engines which are used in a wider range of models and platforms, and this allows the manufacturers to sell cars in various markets with different regulations without having to spend money developing and designing different engines to fit these regulations. This also allows for a single engine to be used by different brands, tuned to suit their particular market.
Chip tuning refers to changing or modifying an EPROM chip in a car's or other vehicle's electronic control unit (ECU) to achieve better performance, whether it be more power, cleaner emissions, or better fuel economy.
This was done with early engine computers in the 1980s and 1990s. Today, the term chip tuning can be misleading, as people will often use it to describe ECU tuning that does not involve swapping the chip. Modern ECUs can be tuned by simply updating their software through a standard interface, such as OBDII. This procedure is commonly referred to as engine or ECU tuning. ECUs are a relatively recent addition to the automobile, having first appeared in the late 1970s.
As technology advanced, so did the electronics that go into cars. The ECU in a modern automobile, together with advanced engine technology, makes it possible to control many aspects of the engine's operation, such as spark timing and fuel injection. The ECU may also control electronic throttle control (drive-by-wire), valve timing, boost control (in turbocharged engines), ABS, the automatic transmission, and the electronic stability control system.
Performance gains are realized by adjusting the ignition timing advance. Higher timing may result in higher performance. However, to cope with advanced timing, one must run high-octane gasoline to avoid pre-ignition detonation or pinging. Manufacturers design for a specific timing and this may limit performance accordingly.
In addition, changing fuel maps to coincide with the stoichiometric ratio for gasoline combustion may also realize performance increase. Most manufactures tune for optimum emissions and fuel economy purposes which can limit performance.
Another reason to change the ECU map is if there are engine, intake, or exhaust modifications to the car. These "bolt-on" modifications alter the way that the engine flows, often causing the air to fuel ratio to change. Without re-mapping the fuel tables, some of the performance gains from the modifications may not be realized.
A common misconception is that the ECU can be tuned to provide different power maps optimized for different driving courses (e.g. race tracks). In fact, once the ECU is tuned for optimal torque at all RPM ranges, there is no reason to "de-tune" the ECU for any RPM. A poorly tuned ECU can result in decreased performance, driveability, and may even cause engine damage.
The most common way to 'upgrade' the ECU is using either plug in modules as mentioned above or using a specialist tuner who will use a device such as CMD Flash or Optican. These devices generally plug into the diagnostic port although in some cases the reprogramming it done directly on the circuit board. Maps are supplied by tuners such as Koch Tuning.
Tuners using the above methods include specialists such as Power Dynamics, and RhinoTuning.
Performance tuning focuses on tuning an engine for motor sport, although many such cars never compete but rather are built for show or leisure driving. In this context, the power output, torque, and responsiveness of the engine are of premium importance, but reliability and fuel economy are also relevant. In races, the engine must be strong enough to withstand the additional stress placed upon it, and so is often far stronger than any mass-produced design on which it may be based, and also that the vehicle must carry sufficient fuel. In particular, the transmission, driveshaft and any other load-bearing powertrain components may need be modified to withstand the load from increased power.
In most cases, people are interested in increasing the power output of an engine. Many well tried and tested techniques have been devised to achieve this, but all essentially operate to increase the rate (and to a lesser extent efficiency) of combustion in a given engine. This is achieved by putting more fuel/air mixture into the engine, using a fuel with higher energy content, burning it more rapidly, and getting rid of the waste products more rapidly - this increases volumetric efficiency. In order to check the amount of the fuel/air mixture, air fuel ratio meters are often used. The weight of this fuel will affect the overall performance of the car, so fuel economy is a competitive advantage. This also means that the performance tuning of an engine should take place in the context of the development of the overall vehicle.
The specific ways to increase power include:
- Increasing the engine displacement by one or both of two methods: "Boring" - increasing the diameter of the cylinders and pistons, or by "stroking" - using a crankshaft with a longer stroke and longer connecting rods, in combination with pistons of shorter compression height (to maintain the original compression ratio).
- Using larger or multiple carburetors, to create more fuel/air mixture to burn, and to get it into the engine more quickly. In modern engines, fuel injection is more often used, and may be modified in a similar manner.
- Increasing the size of the valves in the engine, thus decreasing the restriction in the path of the fuel/air mixture entering, and the exhaust gases leaving the cylinder. Using multiple valves per cylinder results in the same thing - it is often more practical to have several small valves than have larger single valves.
- Using larger bored, smoother, less contorted intake and exhaust manifolds. This helps maintain the velocity of gases. Similarly, the ports in the cylinder can be enlarged and smoothed to match. This is termed cylinder head porting, usually with the aid of an air flow bench for testing and verifying the efficiency of the modifications.
- The larger bore may extend right through the complete exhaust system, using larger diameter piping and low back pressure mufflers, and through the intake system, with larger diameter airboxes and high-flow, high-efficiency air filters. Muffler modifications will change the sound of the car's engine, usually making it louder; for some tuners this is in itself a desirable property.
- Increasing the valve opening height (lift), by changing the profiles of the camshaft or the lift (lever), ratio of the valve rockers (OHV engines), or cam followers (OHC engines).
- Optimising the valve timing to improve burning efficiency - usually this increases power at one range of operating RPM at the expense of reducing it at others. For many applications this compromise is acceptable. Again this is usually achieved by a differently profiled camshaft. See also Four-stroke cycle#Valve Timing, variable valve timing.
- Raising the compression ratio, which makes more efficient use of the cylinder pressure developed and leading to more rapid burning of fuel, by using larger compression height pistons or thinner head gasket, or by milling or "shaving" the cylinder head.
- Forced Induction; adding a turbocharger or supercharger. The fuel/air mass entering the cylinders is increased by compressing the air first, usually mechanically. Further gains may be realized by cooling compressed (and thus heated) intake air with an air-to-air or air-to-water intercooler.
- Using a fuel with higher energy content or by adding an oxidiser such as nitrous oxide.
- Reducing losses to friction by machining moving parts to better tolerances than would be acceptable for production, or by replacing parts. A common example of this is, in OHV engines, replacing the production rocker arms with replacements incorporating roller bearings in the roller contacting the valve stem.
- Reducing the mass of the "rotating mass," which comprises the crankshaft, connecting rods, and pistons. Doing so can improve throttle response due to lower inertia, as well as reduce overall vehicle weight.
- Changing the tuning characteristics electronically, by changing the firmware of the engine management system (EMS). This chip tuning often works because modern engines are designed to give a great deal of raw power, which is then reduced by the engine management system to make the engine operate smoothly over a wider RPM range, with low emissions. By analogy with an operational amplifier, the EMS acts as a feedback loop around an engine with a great deal of open loop gain. Many modern engines are now of this type and amenable to this form of tuning. Naturally many other design parameters are sacrificed in the pursuit of power.
The choice of modification depends greatly on the degree of performance enhancement desired, budget, and the characteristics of the engine to be modified. Intake, exhaust, and chip upgrades are usually amongst the first modifications made as they are the cheapest, make reasonably general improvements (whereas a different camshaft, for instance, requires trading off performance at low engine speeds for improvements at high engine speeds), can often improve fuel economy, generally do not affect engine reliability much (because no moving parts are modified), and are in any case essential to take full advantage of any further upgrades.
Furthermore, tuners may also use analytical tools to help evaluate and predict the effect of modifications on the perfromance of the car.
An engine Overhaul means putting the engine back to factory specifications. This generally involves new Piston rings, bearings and Gaskets. When done by a competent engine builder, you can be confident the engine will perform as new.
A top overhaul only covers the replacement of components inside the cylinder head without removing the engine from the vehicle, such as valve and rocker arm replacement. A full overhaul however covers the whole engine component replacement which requires the engine to be removed from the vehicle, such as replacing the connecting rods and crankshaft bearings. By comparison, a full overhaul service costs more than a top overhaul service.
Rebuild is a marketing term with no fixed definition. It is often taken to mean a professional overhaul with certain parts replaced with new units whether needed or not. For example some rebuilders will always replace the pistons (which often are not replaced during an overhaul unless damaged).
Re-manufactured is a marketing term to mean an engine put together to match factory specifications e.g. "as new". Although often a buyer may take this to mean all-new parts are used, this is never the case. At the very least, the cylinder block will be used, as may most other parts. High-quality rebuilds will often include new pistons and line-boring of the crankshaft and camshaft bores.
In engine blueprinting, all the specifications are double-checked. Usually this indicates closer-than-factory tolerances, with custom specifications appropriate for a street car or a race car.
The goals usually are to:
- Ensure the engine puts out the rated power (because not all mass-production engines put out the rated power) for its manufacturer's design
- Eke more power out of a given engine design, by extra careful measurement and assembly
- balancing of reprocating parts and rotating assemblies, to reduce engine vibrations thus achieving more power due to recover of power "lost" to vibrations
Ideally, blueprinting is performed on components removed from the production line before normal balancing and finishing. If finished components are blueprinted, there is the risk that the further removal of material will weaken the component. However, lightening components is generally an advantage in itself provided balance and adequate strength are both maintained, and more precise machining will in general strengthen a part by removing stress points, so in many cases performance tuners are able to work with finished components.
For example, an engine manufacturer may list a piston ring end-gap specification of 0.003 to 0.005 inches for general use in a consumer automobile application. For an endurance racing engine which runs hot, a "blueprinted" specification of 0.00045 to 0.00050 may be desired. For a drag-racing engine which runs only in short bursts, a tighter 0.00035 to .00040 inch tolerance may be used instead. Thus "Blueprint" can mean tighter or looser clearances, depending on the goal.