Tuner Hits 861 HP With Jeep 4.0-Liter Straight Six Engine Tuning

The engine's horsepower was quadrupled using 20 pounds of boost and water-meth injection.
Chris Young

The Jeep's 4.0-liter straight-six engine's maximum of 190 horsepower and 235 pound-feet of torque made the Jeep famously reliable if a little slow.

A custom builder, Newcomer Racing, has now shown that enough boost, as well as forged internals, can turn Jeep's slow 4.0 into a performance powerhouse. During the process, the company was able to set a Jeep power record.


A record-breaking Jeep 4.0-Liter straight-six

The record-breaking build was assembled in Concord, North Carolina by the people at Newcomer Racing, who set out to smash through the 4.0's longstanding power record of 692 horsepower and 777 pound-feet of torque.

As The Drive reports, the motor was assembled by an impressive assortment of aftermarket parts as well as AMC components, starting with the block from a WJ Grand Cherokee, chosen for its thicker cylinder walls.

Impressive engine tuning

Amongst the modifications were a Holley ECU added to dose fuel through port injection to match the engine's intake charge. An On3 Performance 7675 turbo and an air-to-water intercooler drive this as high as 20 psi.

A water-methanol injection system was also used to cool the intake charge and prevent a knock. Newcomer Racing also partially filled the block, leaving a small passage for coolant circulation, which partially accounts for the Jeep 4.0 reaching an impressive 4.8 liters.

After the modifications, the engine produced 861 horsepower and 881 pound-feet of torque, quadrupling the 4.0's horsepower. It did all of this below its max boost, suggesting that Newcomer Racing could get even higher numbers with future attempts.

Modded versions of the reliably sturdy Jeep and the Jeep engine tunings are nothing new, of course: just this year, we wrote about a one-of-a-kind 1984 Jeep with a Buick engine mounted in its rear. To see a detailed breakdown of the engine assembly, watch the video below.

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