Tuner Boosts Jeep 4.0L Inline-Six Past 1,000 HP—And It’s Not Done Yet

The engine now makes 900 hp more than it did when it left the factory.
Horsepower Monster via YouTube

Share

We may earn revenue from the products available on this page and participate in affiliate programs. Learn more ›

Jeep’s 4.0-liter straight-six engine is iconic. Much like the Ford 300, it’s a down-and-dirty truck engine that stayed in production for decades. Also like the Ford 300, it can make a ton of power when you throw some boost at it. Take this one for example, which runs 27 psi and boasts a dyno sheet showing an unfathomable 1,082 horsepower and 1,017 pound-feet of torque.

It’s the work of Newcomer Racing, who has spent years working with this platform. The North Carolina shop previously built a Jeep inline-six making 861 hp thanks to 20 psi of boost, but now, they’ve cooked up something even crazier. What’s more, the previous build ran water-methanol and fuel injection—this one is carbureted and there’s no meth mixed in.

A recent video posted to the Horsepower Monster YouTube channel shows the build in-depth. The stock block has been bored out to 4.6 liters of displacement, though it retains the factory main caps. There’s an aftermarket cast crank that’s fully counterweighted spinning a set of custom JE forged pistons, and that’s pretty much it for the bottom end. Newcomer Racing did a lot of work to the top end, as you might imagine, with heavily ported aluminum Edelbrock heads, larger valves, and full roller-rockers for handling high revs and valve spring pressures. A 650-cfm Holley carburetor manages fueling and is hooked up to an old-school Clifford cast intake that has also been ported.

Newcomer Racing dyno tested this engine with several setups, including a naturally aspirated configuration. It made 394 hp at 6,100 rpm and 375 lb-ft of torque at 4,600 rpm without the turbo, which is mighty impressive considering the straight-six was set up for boost. From there, they threw on a 72-millimeter Precision turbo and made a super-solid 813 hp at 6,200 rpm and 716 lb-ft of torque at 5,800 rpm. Those boys know how to build a power plant.

As the numbers neared those of their previous record-setter, the crew went full-bore and installed a larger 77-millimeter Pulsar turbo. This was the key to success as they managed 989 hp on the first pull with that blower before running lean on 116-octane Sunoco MaxNOS race fuel. A simple jet change was all they needed to achieve their final four-figure power numbers.

The best result of 1,082 hp and 1,017 lb-ft of torque is believed to be a record for Jeep straight-sixes. It may not stand for long, though, as Newcomer Racing plans to swap this one over to fuel injection. It could handily beat those numbers while also being more controllable from a tuning perspective—a win-win.

It’s great to see platforms like this live on long after they stopped production. While the Jeep 4.0-liter enjoyed a lengthy run from 1987 to 2006, that means it hasn’t been manufactured for 18 years at this point. Still, a select few tuners like Newcomer Racing are keeping it fresh and taking it to new heights. I can’t wait to see where it goes next.

Got a tip or question for the author? Contact them directly: caleb@thedrive.com

 
Best Black Friday Deals

See All Black Friday Sales

Our editors combed through the best early Black Friday deals to bring you the most savings on the products you love.