In car tuning culture, an engine swap is the process of removing a car's original engine and replacing it with another. This may be a like-for-like replacement, or to install a non-factory specification engine. Typically an engine swap is performed for performance, swapping-in a more powerful engine; however, an engine swap may also be performed for maintenance, where older engines may have a shortage of spare parts, and so a modern replacement may be more easily and cheaply maintained. Swapping the engine may have negative implications on the car's safety, performance, handling, and reliability. For example, the new engine's different weight balance over the axles and the overall weight of the car can adversely affect the vehicle dynamics. Existing brakes, transmission, and suspension components may be inadequate to handle the increased weight and power of the new engine with either upgrades being required or premature wear and failure being likely. Insurance companies may charge more or even refuse to insure a vehicle that has been fitted with an engine that is different from its initial configuration. For instance, in jurisdictions such as California—with its strict, arbitrary smog rules—it may not be possible to register a late-model vehicle with an engine swap, even if it can be proven to produce less pollution than the original engine (owing to "visual inspection" rules). Types of engine swaps Swapping to a diesel engine for improved fuel economy is a long established practice; with modern high-efficiency diesel engines, this does not necessarily mean a reduction in performance associated with older-version diesel engine swaps. For the particular application of off-road vehicles, the high torque at low speed of turbo diesels (combined with a fuel economy advantage) makes these conversions particularly effective. However, older non-electronic fuel injection diesel engines were well known for their reliability, especially in wet conditions. An engine swap can either be to another engine intended to work in the car by the manufacturer, or one totally different. The former is much simpler than the latter. Fitting an engine into a car that was never intended to accept that engine may be more laborious and costly; modifying the car to fit the engine, modifying the engine to fit the car, and building custom engine mounts and transmission bellhousing adaptors to interface them along with a custom-built driveshaft. Some small businesses build conversion kits for engine swaps, such as the Fiat Twin cam into a