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500+ HP Compound Turbo 4BT Cummins Engine

Find out what it took to turn a stock 105-hp 4BT Cummins engine into a 500+ horsepower rock crawling beast.

This article is courtesy of Engine Builder.


The folks at Hauk Designs are never resting on their laurels. It’s always full steam ahead and on to the next cool project. We recently shared a post after we saw the Hauk Designs’ Beer Tanker earlier in the year at the 2021 Ultimate Callout Challenge. Now, the shop has teamed up with some of the best shops in the diesel landscape to turn a stock 105-hp 4BT Cummins diesel engine into a 500+ horsepower powerplant.

Why the desire for another 395 horsepower? The diesel engine would be for Kenny’s latest build, a Jeep that’s street-legal, but capable of taking to the rocks in true off-road-Jeep fashion.

The 3.9L 4BT Cummins is a diesel turbocharged engine that utilizes an inline 4-cylinder design. The acronym, 4BT, means four-cylinder, “B” series turbocharged. As such, the engine is often used to power urban delivery trucks. While a stock version is neither powerful nor fast, it is reliable, which is perfect for vehicles used in demanding city driving day after day.

Its relatively small size means it’s perfect for jamming into a vehicle that didn’t come from the factory with a diesel engine installed, making it a favorite for vehicle builders. And it comes with the low-end grunt of a diesel engine that everyone loves.

Kenny Hauk summoned a team of experts to help him awaken the beast within the Cummins 4BT and hit the 500-hp mark. The team included Utah-based Industrial InjectionApex Turbo and Mountain Machine, both based in Michigan, as well as AMSOIL.

Apex Turbo contributed a pair of turbos for a compound setup that would allow the team to jam more air into the cylinders. More air means more fuel, and more fuel means more power. 

Industrial Injection helped boost power and performance with a cylinder head that has been fully CNC ported, hand blended, fire ringed, and features ARP bolts and a fire ring head gasket.

The bottom end is supported by an Industrial Injection girdle with ARP bolts. A 12mm 4BT P-7100 pump is pushing 500cc at 4,000 rpm, feeding 6x.018 R4 injectors. The Performance CNC-ported and hand-blended, higher-flowing cylinder head is running custom spec, oversized, nitrided valves and Industrial Injection 150-lb. HD valve springs. To cap it off, a Stage 2 race cam is being utilized and a 4BT Gorilla girdle kit strengthens the bottom end.

Mountain Machine skillfully and masterfully assembled the Cummins. Not only did they assemble it, they added custom billet parts and the sweet flair of a clear front cover with integrated lighting so you can see the geartrain spin and the AMSOIL flowing through the top-notch Industrial Injection internals. The icing on the cake was a custom valve cover to complete the look.

AMSOIL’s role was to ensure proper engine break-in on the dyno. New cylinder liners, bearings, cam lobes and other engine parts have microscopic peaks on them called asperities. During break in, the goal is to allow a controlled amount of wear to parts to wear down these peaks and help components mate together. This ensures, for example, that the piston rings seat properly against the liners, which increases compression for maximum power. 

A good break-in oil also protects and seasons the cam lobes, so they don’t wear down and negatively affect valve timing, reducing power. Simply put, break-in is vital to building an engine that makes maximum power.

The crew tested the engine at Maybee, MI-based Salenbien Performance, which is owned by Apex Turbo owner Ryan Salenbien. The engine hit 505 horsepower and 810 ft.-lbs. of torque when testing ended due to a broken balancer, but many in the group think there’s more power to be found.

Even if 505 hp is the ceiling, it’s quite an engineering achievement to coax nearly 400 additional hp out of a Cummins 4BT. All said and done, this junkyard diesel JK project is now a Cummins-powered rock crawling beast, and another feather in the cap of Hauk Designs. See more photos below!

Diesel of the Week is sponsored by AMSOIL. If you have an engine you’d like to highlight in this series, please email Engine Builder Editor Greg Jones at [email protected]

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