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"Four Wheel", March 1, 2013



BY Tom Morr

Bye-bye, 3.8L. Pulling the powertrain intact is easiest. 4WS chains on at the bellhousing for balance and control.

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.

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.


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.

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.


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 ½-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.


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.

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.)

INTAKE: Typically, these swaps use the largest cone-style air filter that will fit, bolted directly to the Hemi’s 3½-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.

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.

1 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.

2 Hotwire Auto makes some of the best Hemi swap harnesses. OE plugs are used, so no splicing is required.

3 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.

4 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.

5 Three engine plugs and the PCM plugs must be disconnected prior to pulling the engine. They are color-coded for proper reconnecting.

6 Note any aftermarket-accessory tap locations in the fuse box. Then carefully remove the TIPM, which can be sensitive to electricity. 4WS discovered that a plasma cutter with high-frequency start can fry TIPMs, even with the battery disconnected.

7 Next out is the evaporator actuator. The battery tray must also be removed.

8 The fuel line obviously has to be disconnected. A special tool is required. The factory fuel pump has enough volume to feed even a 7.0L Hemi.

9 Pro trick: 6.1L Hemis have a factory-installed pilot bushing snout for their SRT8 torque converters. This has to be removed to fit the 5.7L torque converter. A puller won’t fit, so 4WS welds a bolt to this pilot snout to remove it.

10 Once the old drivetrain is pulled, the new one can be final-assembled: salvaged 6.1L Hemi and 545RFE automatic with the JK’s stock NP231 bolted on here. 4WS completes the prep by adding the Hotwire harness.
































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