Following is a list of ways to increase the horsepower of your car. Many of them are also applicable to other types of engines.

  • Fuel. Higher quality fuels (e.g. higher octane levels) burn more evenly and consistently, reducing combustion inefficiencies (such as 'knock') and thereby allows the engine to perform better.
  • Fuel additives. A number of additives are available to increase the energy level of fuels, thereby increasing the power derived from the fuel. However, use of inappropriate additives or excessive use of additives can damage an engine and invalidate the warranty. Consequently, one should ensure that the type and quantity of any additives use correspond to the engine manufacturer's requirements.
  • Spark Plugs. The quality of the spark affects the efficiency of the combustion. Consequently, ensuring that your spark plug is clean and unworn is important to both power and efficiency. Replacement of the standard spark plug by a larger or higher quality one can improve performance (consult a mechanic, preferably a specialist, on appropriate plug changes for your car engine).
  • Power accessories. Various accessories, such as turbochargers or superchargers, can be added to increase power. To avoid loss of warranty and possible engine damage, any such changes should correspond to the engine manufacturer's requirements. Note that most of these accessories result in lower fuel efficiency.
  • Reducing accessories. Cars contain a number of accessories, such as air conditioning, which can consume a substantial amount of power and fuel. Avoiding such accessories (or turning them off) can result in a greater percentage of power being available for other purposes (e.g. turning the wheels).
  • Change engine chip or software. Older engines were tuned and adjusted with a screwdriver but many newer engines (including almost all recent cars) are controlled by a small computer, which makes appropriate engine adjustments according to the software loaded in them. A number of companies have specialized in software modifications to improve power (tests have reported improvements of up to 25%) and/or fuel efficiency (tests have reported up to 10% improvements). However, actual increases will depend on circumstances, including the skill with which the software modifications have been designed (there are a number of different companies doing this, not all with the same ability). Furthermore, changes may invalidate the warranty and inappropriate changes may damage the engine. Consequently, although such changes allow substantial improvements at a moderate cost, one needs to be aware of the risks.
  • Improved air flow. Some of the engine's power is used simply by sucking air into the engine, so reducing air intake resistance will increase the power output of the engine. This can be done by simple changes (e.g. cleaning the air filter or replacing it with a larger filter) and more expensive ones (e.g. polished intake manifolds).
  • Reduced exhaust resistance. Some of the engine's power is consumed in pushing out the exhaust, especially through the resistance provided by the muffler and converter. Replacing these by ones that offer lower resistance will result in a higher net power output, although one will need to balance the cost against the relatively small improvement.
  • Improved engine condition. Wear on engine components results in increased friction, greater mechanical power loss, and potential pressure loss in the cylinders (e.g. around leaky valves or pistons). All of these lead to power losses. Careful engine use, combined with correct and timely maintenance, reduces engine wear and the corresponding power loss.

At the more extreme end, one can improve power through rebuilding the engine. Such rebuilds can consist simply of replacing key worn components or can involve substantial changes to the engine design (e.g. replacing engine head and cams. Such major changes should only be made by a qualified professional and only after consideration of the potential costs associated with the potential benefits.

One frequently suggested change to increase horsepower is a 'cold air intake', which feeds the engine with cold air rather than the warm air near the engine. However, this modification has a number of notable disadvantages:

  • Potential dirt or water intake into the engine, due to an intake which is nearer the street level.
  • Possible voiding of engine warranty
  • Increased noise if muffling tubes are removed
  • Possible reduction in acceleration at low end (e.g. when accelerating from a stop), although total power at high end RPMs can be higher

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