How to Increase Horsepower in a Jeep 4.0by Scott Eilers; Updated November 07, 2017
Jeep is a subdivision of the Daimler-Chrysler company which mainly produces off-road and sport utility vehicles. The Jeep 4.0L engine was a six-cylinder engine used in many Jeep vehicles from 1984 to 2003, including the Cherokee and the Wrangler. The engine underwent several changes over its nearly 20 year lifespan, including many internal upgrades that increased the available horsepower of the vehicle. All 4.0L Jeep engines have a variety of performance aftermarket parts available which increase horsepower when installed.
Replace the Jeep cold air intake with a performance aftermarket cold air intake. Performance aftermarket cold air intakes increase horsepower by enhancing the flow of cold air into the engine. They are relatively simple to install without professional assistance and are one of the least expensive performance upgrades available for Jeep vehicles. They may slightly increase engine noise, but are generally free from drawbacks when installed correctly.
Replace the Jeep exhuast system with a performance aftermarket exhaust system. Performance aftermarket exhaust systems increase horsepower by enhancing the flow of hot air out of the engine. They typically require professional installation as access to the underside of the vehicle is needed. They substantially increase engine noise, although many Jeep owners find the louder, more aggressive engine note desirable. However, they also increase emissions and may result in your vehicle losing street legal status in some states. Consult state regulations before performing this upgrade.
Install a forced induction kit onto your Jeep 4.0L engine. Forced induction kits increase horsepower by forcing large amount of air into the air/fuel mixture within the engine itself. They are relatively difficult to install and can be extremely expensive. They also reduce fuel economy, drastically in some situations, and increase overall wear and tear on your Jeep. However, they can more than double the horsepower of your Jeep depending on the size of the turbocharger that you install.
Install a nitrous oxide injection kit. Unlike other performance modifications, nitrous oxide injection kits do not permanently change the functioning of your car. They allow the driver the inject a shot of nitrous oxide into the fuel system with the push of a button or the pull of a level, which provides a large but temporary boost to available horsepower. Such kits are typically designed for straight line racing, and like forced induction kits they will increase overall wear and tear on your Jeep when activated.