Editing Engine tuning (section)

==Performance tuning==
{{Unreferenced section|date=December 2018}}
Performance tuning is the tuning of an engine for [[motorsport]]s. Many such automobiles may never compete but are built for show or leisure driving. In this context, the power output (e.g. In [[horsepower]]), [[torque]], and [[throttle response|responsiveness]] of the engine are of premium importance, but reliability and [[fuel efficiency]] are also relevant. In races, the engine must be strong enough to withstand the additional stress placed upon it and the automobile must carry sufficient fuel, so it is often far stronger and has higher performance than the mass-produced design on which it may be based. The [[transmission (mechanics)|transmission]], [[driveshaft]] and other load-transmitting [[powertrain]] components may need to be modified to withstand the load from the increased power.

There are many techniques that can be used to increase the power and/or efficiency of an engine. This can be achieved by modifying the [[air-fuel mixture]] drawn into the engine, modifying the static or dynamic [[compression ratio]] of the engine, modifying the fuel used (e.g. higher [[octane]], different fuel types or chemistries), injection of [[Water injection (engine)|water]] or methanol, modifying the timing and dwell of ignition events, and compressing the intake air. [[Air fuel ratio meter]]s are used to accurately measure the amount of fuel in the mixture. Fuel weight will affect the performance of the car, so fuel economy (thus efficiency) is a competitive advantage.

Ways to increase power include:
* Increasing the [[engine displacement]] by one or both of two methods: "[[Bore (engine)|boring]]" - increasing the diameter of the [[cylinder (engine)|cylinder]]s and [[piston]]s, or by "stroking" - using a [[crankshaft]] with a greater throw.
* Replacing a stock [[throttle body]] with either a larger throttle body (Since it increases airflow due to its larger bore size<ref>{{cite web | url=https://automodifying.com/does-a-bigger-throttle-body-increase-horsepower/#:~:text=Added%20Power,those%20power%20gains | title=Does a Bigger Throttle Body Increase Horsepower? | date=8 August 2019 }}</ref>), an [[electronic throttle control|electronic]] throttle body that opens quickly so that it can access airflow sooner (Which improves [[throttle response]]), or a combination of both. 
* Using larger or multiple carburetors to create a more controllable air/fuel mixture to burn and to get it into the engine more smoothly. [[Fuel injection]] is more often used in modern engines, and may be modified in a similar manner.
* Increasing the size of the [[poppet valve]]s in the engine, thus decreasing the restriction in the path of the fuel–air mixture entering the cylinder and the exhaust gases leaving it. Using [[multi-valve|multiple valves]] per cylinder results in the same effect, though it is often more difficult to fit several small valves than to have larger, single valves due to the [[valve gear]] required. It can also be difficult to find space for one large valve in the inlet and a large valve on the outlet side, and sometimes a large exhaust valve and two smaller inlet valves are fitted.
* Using larger bored, smoother, less-contorted [[inlet manifold]] and [[exhaust manifold]]s helps maintain the velocity of gases. The ports in the [[cylinder head]] can be enlarged and smoothed to match. This is termed [[cylinder head porting]]. Manifolds with sharp turns force the air–fuel mix to separate at high velocities because fuel is denser than air.
* The larger bore may extend through the [[exhaust system]] using large-diameter piping and low [[back pressure]] [[muffler]]s, and through the [[intake system]] with larger diameter [[airbox]]es and high-flow, high-efficiency [[air filter]]s. Muffler modifications will change the sound of the engine, usually making it louder.
* Increasing the [[valve opening height]] (lift) by changing the profiles of the cams on the [[camshaft]] or the [[lever]] (lift) ratio of the valve rockers in [[overhead valve]] (OHV) engines, or [[cam follower]]s in [[overhead cam]] (OHC) engines.
* Optimizing the valve timing to improve burning efficiency; this usually increases power at one range of operating [[revolutions per minute|RPM]] at the expense of reducing it at others. This can usually be achieved by fitting a differently profiled camshaft.
* Raising the [[compression ratio]] by reducing the size of the combustion chamber, 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]]s or by using a [[milling machine]] to "shave" the [[cylinder head]]. High compression ratios can cause [[engine knock]] unless [[high-octane fuel]]s are used.
* [[Forced Induction]]; adding a [[turbocharger]] or a [[supercharger]]. The air/fuel mix entering the cylinders is increased by compressing the air. Further gains may be realized by cooling the compressed intake air (compressing air makes it hotter) with an [[air-cooled intercooler|air-to-air]] or [[water-cooled intercooler|air-to-water]] intercooler.
* Using a fuel with higher energy content and by adding an [[oxidizer]] such as [[nitrous oxide]].
* Using a fuel with better knock suppression characteristics (race fuel, E85, methanol, alcohol) to increase timing advance.
* Reducing losses to friction by machining moving parts to lower tolerances than would be acceptable for production, or by replacing parts. This is done In overhead valve engines by replacing the production rocker arms with replacements incorporating roller bearings in the roller contacting the valve stem.
* Reducing the rotating mass comprised by the [[crankshaft]], [[connecting rods]], [[piston]]s, and [[flywheel]] to improve throttle response due to lower rotational inertia and reduce the vehicle's weight by using parts made from alloy instead of steel.
* Changing the tuning characteristics electronically, by changing the [[firmware]] of the [[Engine control unit|EMS]]. This ''[[chip tuning]]'' often works because modern engines are designed to produce more power than required, which is then reduced by the EMS to make the engine operate smoothly over a wider [[revolutions per minute|RPM]] range, with low emissions. This is called de-tuning and produces long-lasting engines and the ability to increase power output later for facelift models. Recently emissions have played a large part in de-tuning, and engines will often be de-tuned to produce a particular carbon output for tax reasons.
* Lowering the underbonnet temperature to lower the engine intake temperature, thus increasing the power. This is often done by installing [[thermal insulation]]&nbsp;– normally a heatshield, [[thermal barrier coating]] or other type of [[exhaust heat management]]&nbsp;– on or around the exhaust manifold. This ensures more heat is diverted from the under-bonnet area.
* Changing the location of the air intake, moving it away from the exhaust and radiator systems to decrease intake temperatures. The intake can be relocated to areas that have [[Ram-air intake|higher air pressure due to aerodynamic effects]], resulting in effects similar to [[forced induction]].

The choice of modification depends on the degree of performance enhancement desired, budget, and the characteristics of the engine to be modified. Intake, exhaust, and chip upgrades are usually among the first modifications made because they are the cheapest and make reasonably general improvements. A change of camshaft, for instance, requires a compromise between smoothness at low engine speeds and improvements at high engine speeds.