How to Hemi Convert a JT Gladiator

If you own or are thinking of owning a JT Gladiator in Australia than no doubt you will have considered a Hemi conversion and followed some online who have done it.

Swapping a HEMI V8 into a Jeep Gladiator is one of those builds that sits right at the intersection of engineering ambition and off-road obsession. It’s not a simple bolt-in weekend job, but with the right planning, fabrication skills, and patience, it can transform a capable truck into a seriously powerful off-road machine.

The Jeep Gladiator was originally designed around the Pentastar V6, so fitting a larger HEMI V8 requires more than just engine replacement. The first major consideration is choosing the donor engine. Most builders opt for the 5.7L or 6.4L HEMI from Chrysler, Dodge, or Ram vehicles because they offer strong aftermarket support and relatively straightforward ECU integration compared to older V8 swaps.

Once the engine is selected, compatibility becomes the next hurdle. The engine mounts will not line up with the factory Gladiator frame, so custom fabrication or a purpose-built swap kit is typically required. These kits usually include engine mounts, transmission adapters, and sometimes oil pan modifications to clear the front differential and axle articulation during off-road use.

Transmission pairing is another critical step. Many builders choose the 8HP automatic transmission from Stellantis vehicles because it pairs well with modern HEMI engines and offers excellent torque handling. However, integrating it with the Gladiator’s drivetrain requires attention to transfer case compatibility, driveshaft length adjustments, and ensuring the gearing matches your tire size and intended use.

Electronics are often the most complex part of the swap. Modern HEMI engines rely heavily on ECU integration, CAN bus communication, and electronic throttle control. You may need a standalone engine management system or a reprogrammed factory ECU to make everything work seamlessly with the Gladiator’s dashboard, ABS, and traction control systems. Companies specializing in HEMI swaps often provide wiring harness solutions that simplify this step significantly.

Cooling and exhaust systems also need upgrades. A larger aluminum radiator with high-flow fans is usually required to handle the increased heat output of a V8, especially in low-speed off-road conditions. The exhaust system must be custom-fabricated to clear the frame rails and suspension components while maintaining proper clearance for articulation.

Suspension and braking upgrades are not optional. The added weight and power of a HEMI V8 require stronger springs, reinforced control arms, and performance shocks to maintain stability both on and off-road. Brake upgrades, often including larger rotors and multi-piston calipers, ensure the vehicle can safely manage the increased performance.

Finally, tuning and testing bring everything together. A professional dyno tune ensures the engine runs efficiently with the new setup, while real-world testing helps identify any drivetrain binding, overheating issues, or electronic faults.

In the end, swapping a HEMI V8 into a Jeep Gladiator is a serious project that blends fabrication, electronics, and mechanical expertise. While challenging, the reward is a uniquely powerful truck that retains its off-road DNA while delivering muscle car performance on demand. But What Does it Actually Cost to do it?

The Kits available to do it start from $70,000 AUD add to this you need a Gladiator in the first place and the labour involved to do it. At the time of publishing this build is estimated to be a $110K build.

Want to be the first to have this done by the team at GDL? reach out to us. We would love to sink our teeth into a build like this.

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