This all day. If there was ever a better article written stating the case for putting a diesel in a JK, here you go:
https://www.bruiserconversions.com/news/bruiser-jeep-wrangler-jk-cummins-diesel-conversions
Diesel Bruiser Conversions is swapping Cummins diesels into not only CJ, YJ, and TJ Jeeps, but has perfected the JK Wrangler swap, as well. The Cummins mill and GM transmission interface with the JK’s CANbus system and there are no warning lights or issues. Jeff’s Jeep Yard in Florida, River Raider Off Road in Pennsylvania, and Trail Jeeps in Colorado are performing the Diesel Bruiser conversions.
Diesel Bruiser Conversions removes the 3.8L engine and 42RLE factory automatic and replaces it using the 4BT Cummins turbo diesel, utilizing Bruiser conversion brackets, a mechanical bellcrank assembly with Lokar stainless throttle and t.v. cable for the Raptor 700R4 automatic, as well as a bracket for the floorboard to accept a manual throttle pedal. An AC and alternator bracket enables the swap to re-use the existing AC compressor and alternator from the 3.8L. The serpentine belt is upgraded to an eight groove belt, along with the AC clutch and alternator pulley.
The 4BT is highly modifiable, has multi-fuel capability, produces fantastic torque off-idle, and has the capability to go 500,000 miles without a rebuild. You can see the front dress includes the OE alternator and AC compressor that have eight groove pullies installed so they work with the eight groove serpentine belt that’s a part of this conversion.
Custom AC lines go to the factory compressor in its new location. The battery tray relocates the battery and the fuse /relay box for proper clearance for the cold air intake and turbo. The wiring harness is completely re-engineered to control all engine functions as well as communicate with the factory ECM through a S.I.M. (Systems Integration and Management) computer.
The hydraulic motor mounts are designed to remove the 4BT’s vibration and are located in the custom engine mounting bracket assembly. The gear-driven power steering pump for the 4BT is utilized and high-pressure and return lines are custom made to connect to the OE power steering gearbox. The pump makes enough pressure to operate aftermarket ram assist or full hydraulic steering systems as it’s designed to operate a hydroboost brake assist system.
The Bruiser 4BT four-cylinder Cummins conversion fits the JK as if it came from the factory. The stock radiator is retained and works fine, even in hot desert environments.
The factory radiator and fan assembly are retained. The 4BT does not require an extreme cooling system to maintain the proper temperature range of 180-degrees F. The lower water neck is replaced with a custom-built neck that allows you to re-use the factory lower hose from the 3.8L. The upper hose is replaced.
The braking system is controlled by a Stainless Steel Brake Corporation (SSBC) vacuum pump and reservoir canister to create vacuum for the braking system due to the diesel engine’s inherent lack of vacuum. The engine is mated to the 700R4 Raptor transmission through a Bruiser adapter and flexplate. The transmission is mated to the factory transfer case through a custom adapter and broached tailshaft assembly. The cooling lines are custom for the transmission as are all brackets to attach the factory shifter cables to the transmission and transfer case. This allows re-use of OE transmission and transfer case shifters in their factory locations. OE-length drive shafts work with up to six inches of lift.
Jeff’s diesel JK is producing 402 lb-ft of torque at 2,100 rpm (off-idle torque is 280 lb-ft!) and 140 hp at 2,700 rpm. It’s returning 28 mpg in the city and 32 on the highway. It handles as a JK should and works well off-road. With all that low-rpm torque, you seldom have to spin a tire in the dirt with the Bruiser.
