Big tires on Jeeps often equal a lack of power to the ground. Superchargers can help, but they aren’t a true replacement for displacement.
Bye-bye, 3.8L. Pulling the powertrain intact is easiest. 4WS chains on at the bellhousing for balance and control.
Chevy V-8 swaps into Jeeps are fairly refined, particularly LS-based jobs. But some Jeep owners want to stay true to the bloodlines. That narrows down the popular choices to the AMC V-8s, the Mopar Magnums, or the Gen III Chrysler Hemis. The latter give the best combination of power and efficiency—about 1 hp per cubic inch (SAE net). This article is devoted to the Hemis.
4x4 shops have done hundreds of Wrangler Hemi swaps in recent years. 3.8L JKs are notoriously underpowered, as is any late-model Jeep that runs large tires. Fat-walleted Jeeps owners simply write a $20,000-plus check to a competent shop to have a crate Hemi swapped in. Companies such as AEV and Burnsville Off-Road even offer complete DIY swap kits.
We researched a more à la carte route for JK owners who are considering doing the swap at home. Kevin Wyas, owner of 4WS (aka Missouri 4Wheelers Supply), showed the highlights of what the hands-on late-model Jeep owner needs to know to do a Hemi swap, using a ’07 JK as an example. Wyas estimates DIY cost savings at more than $5,000, depending on the cost of junkyard parts.
Hemis
The “modern” 5.7L Hemi was introduced for the ’03 model year. Since this Gen III V-8 family is just a decade old, it isn’t nearly as prevalent in junkyards as GM LS engines—a lower supply keeps prices higher.
5.7L: The most cost-effective Hemi repowering engine for Wranglers, it has appeared in Chrysler products since 2003: Ram, Durango, Grand Cherokee/Commander, Challenger, Charger, Magnum, and Aspen. Truck versions are typically rated around 345 hp/375 lb-ft while the R/T car version punches in as high as 340 hp/390 lb-ft. Beginning in 2009, Variable Valve Timing (VVT) bumped truck applications up to 390/407. Salvaged VVT-equipped engines are harder to find than the older-model Hemis. They’re also more difficult to swap into ’12-current JKs thanks to the “locked” computer and special wiring harness.
6.1L: This block features a larger bore and other cooling and oiling differences compared to the 5.7L. It appeared from 2005-2010 in the various Chrysler family SRT-8 packages. Rated at 425/420, this engine doesn’t have VVT.
This particular 6.1L Hemi was involved in some horse trading, so it arrived at 4WS as more of a long-block than a complete engine. Brennan Dodge was our source for the missing OE accessories.
6.4L: Basically a bored-out 6.1L with VVT added, the 6.4 was introduced as the 399 Hemi crate engine in 2007, with an assembly line version appearing in the ’11 Challenger SRT-8—rated at 470/470.
6.7L: This is a stroked and heavily modified 5.7L, putting out about 520/535.
7.0L: Known as the 426 Hemi crate engine, this Mopar offering is rated at 540/540.
Currently, Mopar offers three Gen III Hemi crate packages for those who want clean power on a pallet: 5.7L Eagle (VVT), 6.1L and 426 (7.0L).
The engine will need a Dodge truck steel rear-sump oil pan or a fancier aluminum Grand Cherokee WK SRT-8 pan.
Transmissions
The most popular Hemi-compatible transmission for a JK swap is the pre-’11 545RFE five-speed automatic—it bolts up the to the Hemi and NVG231/241 transfer cases. The 545RFE has been Chrysler’s 1⁄2-ton five-speed automatic of choice since 2001, appearing behind the 3.7L, 4.7L, and 2.8L CRD in Rams, Grands, Libertys and Dakotas/Durangos. Production numbers/availability make it the most cost-effective option.
Another auto option that Burnsville has successfully done in ’12-current (3.6L-replacement) swaps is the W5A580 five-speed transmission. This Mercedes-built automatic is available in the ’12 to current JK as well as the Durango and in earlier Chrysler 300s/Magnums/Chargers/Challengers. This job is essentially transplanting a Grand Cherokee WK or Commander (XK) powertrain: 5.7L or 6.1L mated to the five-speed.
For people who want a stick, the Liberty/current JK/Durango NSG 370 six-speed manual is apparently possible. Web searches reveal varying opinions on its viability.
Ancillary
4WS compiled a shopping list of the other parts required to put our salvaged 6.1L Hemi and 545RFE into a JK. A few details:
Wiring harness: The biggest headache is making the new engine compatible with the vehicle’s other electronics, such as traction control (ESP). Wiring whiz Tony Squire of Hotwire Auto has created engine-conversion harnesses for years. For TJs and JKs, Hotwire Auto offers plug/play harnesses for 5.7L and 6.1L swaps as well as reflashed PCMs for these conversions. Hotwire is also the source for the necessary A/C lines.
PCM: The Hemi PCM needs to be reflashed for the specific swap to be compatible with the JK’s electrical system. Our particular engine passed through a few hands. It’s a 6.1 block rumored to have been bored to 6.4L for a project vehicle that never happened. Burnsville Off-Road owner Dan McKeag was familiar with this particular engine and remembered its block being a stock 6.1L from an ’06 Chrysler 300 SRT-8. (Several engine accessories were missing when 4WS took possession.) Burnsville flashed a PCM for it.
Hotwire Auto makes some of the best Hemi swap harnesses. OE plugs are used, so no splicing is required.
Cooling: Radiator space is tight in a JK, limited to the OE depth (single-row). The popular JK Hemi swap radiators use cost-conscious epoxy construction. Out of curiosity, we contacted C&R Racing with a “what if?” on a fully welded radiator. The company has a long-standing record with cooling systems for NASCAR, IndyCar, and SCORE race vehicles. C&R baselined a stock JK radiator and created a fully brazed cross-flow model for not a whole lot more than the existing epoxied units. Vibration-resistance is the biggest brazing benefit. (This particular JK also had an existing AEV Heat-Reduction Hood. For trans cooling, 4WS likes the B&M SuperCooler.)
Overheating is a common headache in V-8–converted Jeeps. Aftermarket epoxy-style swap radiators are proven effective, but C&R Racing accepted the opportunity to prototype a fully welded cross-flow unit.
Intake: Typically, these swaps use the largest cone-style air filter that will fit, bolted directly to the Hemi’s 31⁄2-inch MAS. 4WS used an Airaid filter and wrap.
Exhaust: 4WS recommends upgrading the entire system for optimal flow. The solution here was a MagnaFlow 3-inch Hot Rod Builder’s Kit with a single stainless muffler and spun 49-state MagnaFlow universal 3-inch cats. JK owners should investigate local emissions regulations when designing their exhaust system.
4WS recommends upgrading to a 3-inch exhaust to let the Hemi exhale fully. The shop showed off its stainless MIG skills by using a stainless steel Magnaflow Hot Rod Builder’s Kit with a single muffler and two spun Magnaflow universal cats.
Incidentals: Fuel line fittings are necessary to tap the existing JK lines into the Hemi. 4WS recommends the Russell parts listed here. The shopping list also includes OE engine accessories, some of which might already exist on junkyard Hemis.
Next month we’ll show how 4WS makes everything fit. We’ll also touch on troubleshooting/what happens when the vehicle rejects the donor organs.
PhotosView SlideshowHere are necessary OE Chrysler parts. Using a complete Hemi will cut down this list. Oil pan part numbers are for a rear-sump Ram steel unit. Qty Item PN 1 Alternator 56044380AJ 1 Alt Bolt 1 6504344 1 Alt Bolt 2 6101985 1 Tensioner Bolt 6102381AA 1 Steering Pump 5290778AA 3 Steering Bolt 6102184AA 1 Tensioner 04861660AA 1 Idler Pully 4792835AA 1 A/C Compressor 55116917AD 1 Belt 53013676AC 8 Engine Mount Bolts 0614214AA 2 Engine Mount Frame Bolts 06508081AA 2 Engine Mount Frame Nuts 6502585 1 Engine Mount 1 52090304AG 1 Engine Mount 2 52090305AG 4 O2 Sensor 56029049AA 1 TIPM 56049717AO 1 Air Intake Hose 5037774AB 1 Flex Plate 4736604AA 4 Bell Housing Bolts 6022266 2 Bell Housing Bolts 6036455AA 1 Structural Dust Cover 53021491AA 8 Structural Dust Cover Bolt 6101985 1 Intermediate Plate 52104344AA 1 Starter 56044736AC 2 Starter Bolts 6101985 1 Dipstick 53013991AB 1 Dipstick Tube 53013685AF 1 Dipstuck Tube Bolt 6504785 1 Trans Shift Bracket 52104371AG 2 Trans Shift Bracket Bolt 6508738AA 1 Trans Shift Lever 52109706AC 2 Trans Cooler Line Clip 52079789AB 1 Trans Cooler Lines 55038175AA 1 Exhaust Manifold Gasket 1 5038098AA 1 Exhaust Manifold Gasket 2 5038099AA 1 Oil Pan 53021334AF 1 Oil Pan Pick Up 53021522AE 1 Oil Pan Pick Up Bolt 6506333AA 1 Oil Pan Pick Up Nut 6502756 1 Windage Tray 53021568AE 19 Oil Pan Bolts 6508065AA 3 Oil Pan Bolts 6508066AA 1 Engine Dipstick 53021858AD 1 Engine Dipstick Tube O-Ring 53021144AA 1 Engine Dipstick Tube 53021859AC
4WS has completed dozens of Jeep Hemi swaps using these aftermarket parts. Qty Item Mfg. P/N 1 Wire Harness Hotwire R-0027 1 A/C Hoses Hotwire R-AA2109 1 PCM Burnsville 5094870AE 1 Radiator C&R Custom 1 Trans Cooler B&M 70255 1 Air Filter, Wrap Airaid 700-457, 799-456 1 Radiator Hose, Upper NAPA 7369 1 Radiator Hose, Lower NAPA 7390 1 Fuel Fitting 1 Russell 640850 1 Fuel Fitting 2 Russell 640860 1 Fuel Fitting 3 Russell 640160 2 Catalytic Converters Magnaflow 59959 1 3” Hot Rod Ehxaust Builder’s Kit Magnaflow 10703 1 Muffler Magnaflow 14259
