The 4.0 straight-six AMC engine inside many late-’80s through early-’00s Jeeps was one of the best Jeep motors ever. It was extremely reliable, had great performance for its time, and was capable of taking the Wranglers and Cherokees it was inside anywhere. Still, it is woefully underpowered by today’s standards. With the 2023 Wrangler V8 capable of an astonishing 470 horsepower and identical torque, the 173-190 horsepower from the Jeep 4.0 is lacking. So today we’re looking at the best Jeep 4.0 turbo kit on the market to take your Wrangler TJ and other 4.0 Jeep vehicles.
Read on to find the best Jeep 4.0 turbo kits available. Make sure to check out our other Jeep content, including our Jeep 4.0 engine guide,Ultimate Jeep 4.0 mod guide, Jeep Grand Cherokee vs Toyota 4Runner comparison, and our Jeep Wrangler reliability and common problems guide.
Jeep Turbo Kit Basics
While many don’t realize it, the builder of the Jeep’s 4.0 straight-six engine was actually the American Motor Company. AMC built the engine from the 1987–2006 model years, and it’s an overhead valve engine (OHV) that is naturally aspirated. Both the engine and the block are cast iron, and compression ranges from 8.8:1 to 9.2:1, making it ideal for turbocharging. Over the years, AMC/Jeep gave the engine several upgrades, including improving the fuel injection system and reinforcing the block.
Over the years, many people have taken to modifying their AMC/Jeep 4.0 to increase the horsepower and torque. Stock, the engine makes 173-190 horsepower and 220-235 lb-ft of torque. While that is not bad, especially for the 1990s, by todays’ standards it’s certainly lacking. Granted, if you’re buying a Wrangler you aren’t looking to win any horsepower contests. Still, the extra power — especially the low-end torque — is always beneficial.
Some people opt for supercharging their Jeep, which is easier, but adding a turbo is another option. Due to the engine being naturally aspirated from the factory, in order to add a turbocharger you need to have a whole new turbo-exhaust manifold. In addition, you’ll also need all oil and/or coolant lines, an intercooler, a full exhaust, new air intake, the turbocharger, and new brackets for the turbo and intercooler.
Jeep 4.0 Turbo Upgrades Horsepower Gains and Power Limits
Depending on the size of your Jeep 4.0 turbo kit, you can add a lot of horsepower and torque to your engine. Your standard kits will run less than ~8 PSI or less of boost and put your engine around 250 wheel-horsepower. If you want even more, you can always run a larger turbocharger. However, the larger your turbo the more lag you will experience, which will really hurt the Jeep when off-roading or crawling.
In addition to making sure you don’t go with too big of a turbo, you’ll also need to make sure you have all necessary supporting mods for your build. In addition to the components talked about above, you will also want new colder spark plugs and larger fuel injectors. The colder spark plugs will help reduce cylinder pressures and temperatures. The larger injectors will allow the engine to be properly fueled to avoid risking detonation or pre-ignition. You’ll also need a 2 bar MAP sensor for the ECU to compensate for the boost.
Generally, for the stock internals, you will want to keep power below 300 wheel-horsepower. If you plan on going more, you will definitely want to upgrade the pistons and rods to forged steel versions. In addition, if you plan on running more than 7-8 PSI of boost, you will run into head gasket issues. Head studs help, but that’s generally the most these engines can reliably take before cylinder pressures are too great.
Best Jeep 4.0 Turbo Kits
The best Jeep 4.0 Turbo Kits are:
- Racing Solutions Legend Turbo Kit
- MMI Speed Shop Turbo Kits
- Custom Jeep Turbo Kit
There are a few different options for Jeep 4.0 turbo kits, which range from solid to quite poor. For many years, the Banks Power Sidewinder turbo kit was extremely popular and very reliable. Unfortunately, Banks Power has stopped manufacturing the kit, making it almost impossible to still find. There are a ton of different budget setups with cheaper parts, which will still make power but are not nearly as reliable.
Another popular route is to create your own custom turbo kit, sourcing all of the components yourself. For those who want to take this option, we’ll give you a basic guide to get your 4.0 Jeep turbo upgrade started. Let’s start with one of the newest entries to the Jeep 4.0 turbo kit game, the Racing Solutions Legend kit.
1) Racing Solutions Jeep 4.0 Turbo Kit
While it is a very new entry to the list, the Racing Solutions Legend Jeep turbo kit is the top option on the market. Built and created by a Jeep enthusiast, this should definitely be your number option if you can afford it. The turbo kit comes with everything you need for a full conversion, including all exhaust components, a blow-off-valve, a new airbox, and all fueling upgrades. They also have a tuning solution so you can get the most bang for your buck.
The turbo kit promises 250 wheel-horsepower with 93 octane, and can fit either manual or automatic transmissions. The turbo is a journal bearing Precision 5431E MFS, and the kit comes with a air-to-water intercooler and heat exchanger. Air-to-water intercoolers with heat exchangers are substantially better than traditional air-to-air intercoolers, and allow for superior cooling.
Overall, this is the best Jeep 4.0 turbo kit on the market, though it is a bit more expensive than most of the others. It is designed to fit the Jeep Wrangler TJ (2000–2006), and it runs ~$5,000 when it’s on sale.
2) MMI Speed Shop Budget Jeep Turbo Kit
Next up on our list is our budget option, the MMI Speed shop Jeep turbo kits. These kits are coming in at just over $1,300-$1,500, making them an excellent value for what they provide. The MMI Speed Shop kits promise a 40% increase in horsepower over stock, with the option to get an even larger turbo. The included turbo is a hybrid T3/T4 turbo with a 0.57-mm compressor wheel with 0.50 a/r compressor housing and 0.63 a/r turbine housing.
Additionally, the MMI kit also comes with a large intercooler that has a claimed 2% pressure drop, which is pretty good. MMI markets the intercooler as a front-mount, but all pictures appear to show a top-mounted intercooler, instead. Other components include a dump pipe, new intake, boost controller, blow-off-valve, and downpipe. There does not appear to be any fueling upgrades, so those will need to be sourced separately.
The MMI Speed Shop 4.0 Jeep turbo kit is a solid kit that is great for budget builds. The kit fits 1997–2006 Jeep Wranglers (TJ), though the 1997–1999 Wranglers will need a newer 2000+ intake manifold.
3) Custom Jeep 4.0 Turbo Kit
For our final Jeep 4.0 turbo kit recommendation, we suggest making your own custom turbo kit by sourcing the parts individually. There are many Ebay and knock-off turbo kits, and most of them are just unreliable junk. If you really want a budget kit, go with the MMI above. But, if you want a more reliable kit while staying below the Racing Solution Legend kit price point, custom is the best way to go.
At a minimum, for a custom kit, you will need a turbocharger and all components, new exhaust manifold or up-pipe to existing manifold, downpipe, piping from the turbo to the throttle body, turbo mounts (to the engine), new intake, larger fuel injectors, and all oil and coolant lines for the turbo to cool. An intercooler is optional, but will be very helpful when it comes to hotter days and under heavy use.
The hardest part to source will be the exhaust manifold and intercooler piping. A popular turbo exhaust manifold for the 4.0 Jeep comes from Boostwerks Performance. Their turbo manifold allows for a direct bolt-in turbo setup and fits 1991–2001 Jeep 4.0s. From there, 505 Performance makes turbo brackets and sells an intercooler. They also have their own kits, but you have to be in the New Mexico area for them to install it.
Overall, a custom turbo kit should provide you with solid reliability and as much performance as you want. You will likely need some custom fabrication, but custom kits can be very rewarding to build and create.
Jeep Turbo Kit FAQ
Yes, there are many different kits out there to turbocharge your Jeep 4.0 straight-six. The best kit comes from Racing Solutions now that the Banks Power kit is discontinued. With a proper Jeep 4.0 turbo setup, you can make more than 250 wheel-horsepower.
Most people will keep the boost in a 4.0 Jeep to 7-8 PSI or less. Many people have experienced problems with head gasket leaks when pushing more than 8 PSI of boost, making that the maximum most will run on a stock engine.
There are many different kits out there to turbocharge your Jeep 4.0 straight-six. The best kit comes from Racing Solutions now that the Banks Power kit is discontinued. With a proper Jeep 4.0 turbo setup, you can make more than 250 wheel-horsepower.