2004 was the sixth and last model year of the WJ Grand Cherokee and a lot of Jeep enthusiasts were hoping for a high-performance engine option, just like what came out for the 1998 model, the last year of the ZJ series. At the end of that model year, Jeep introduced a "best-in-class" 5.9-Liter engine option for the Limited, an option that ended up being very popular and amassing sales of nearly 15,000 units. Jeep had whetted everyone's appetite with the "HO" version of the 4.7-liter engine that was introduced for 2002, but customers wanted more than the extra 30 HP that it offered.
As the 2004 model year progressed, rumors kept surfacing with some sources saying that Jeep was in fact testing WJs with the 5.7 Hemi engine. What they didn't know at the time was that some of these test "mules" were actually 2005 WK Grand Cherokees, but with modified front sheet metal from 2004 models. This was one of the reasons that some industry sources were saying early on that the front end of the WK was going to look nearly identical to the WJ. But early WK mock-ups and test mules used some of the existing sheet metal until Jeep was ready to stamp out new parts with the WK specs. The hood and fenders had to be 4" longer in order to accommodate the larger Hemi engine.
A couple of years ago, not long after the new 5.7 Hemi was introduced, the engine was made available in "crate" form, as is done with most factory engines. The engines, we are told, were swapped into some older vehicles, but no one had attempted to try one in a modern production vehicle until a Montana company modified a Wrangler in 2002.
Fitting and configuring a Hemi into a Wrangler presented a few challenges. The Hemi engines are designed with the NGC Bus protocol while the Wrangler featured JTEC. A custom computer had to be built to emulate some of the Dodge functions to make everything work correctly. Fortunately, the narrow/tall Hemi engine was fit into the engine compartment with very few body alterations, although very snugly. It is actually easier to fit the 5.7 Hemi engine into the Wrangler than a 4.7 which is lower and wider. All other issues were overcome, with all of the factory functions and diagnostics retained.
The question is, if a 5.7 Hemi engine can be swapped into a Wrangler, a "smaller" vehicle, why can't it be done in a WJ Grand Cherokee? As soon as Hemi crate engines became available, WJ owners were inquiring about the possibilities of buying one and having it swapped into their Jeeps. When it became apparent that Jeep was not going to build a Hemi WJ version during the last model year, even more owners were anxious to try and have this done.
In early 2003 we contacted one of the engineers at Jeep and inquired about the possibility of swapping a 5.7 crate engine into a WJ. He told us that it would be "major surgery", if at all even possible. First, the entire engine compartment would have to be repackaged. The ABS system and brake lines would all have to be moved as well as all of the engine hoses and wiring. Since the Hemi uses an electronic throttle ("drive by wire") the Dodge PCM would have to be modified, or more likely, an aftermarket computer would have to be built and programmed for a lot of vehicle functions as was done with the Wrangler Hemi. The complex engine wiring would be another challenge as Dodge harnesses would have to be incorporated and modified.
And that's just for starters. Since the 4.7 engine is low and wide, the taller and narrower Hemi engine would be a difficult fit. The suspension would have to be lifted and other engine bay modifications performed as well. According to American Expedition Vehicles, the conversion of the JTEC to the NGC type controller would be much more complex for a WJ than what was required for the Wrangler. The Wrangler has a lot less feature and programming requirements.
Finally, there is the issue of emissions (and CARB certification for some States), gauges, air conditioning, cruise control and so on. Did we mention cost yet? The Wrangler Hemi conversions costs around $18,000 (less some credit for existing engine & parts). A WJ conversion would probably run well over $20,000.
The bottom line, it appears, is that it is not only economically not worth the swap, but perhaps physically and electronically just about impossible. The best advice for WJ 4.7 owners wanting a lot more power would be to look into a Kenne Bell supercharger, at under $5,000 the cost is about 1/5th of a what Hemi swap would be (if it were even possible). For those not wanting the hassles of keeping a supercharged engine "in tune", and who gotta have a Hemi in their Grand Cherokee are left with one choice - to buy a new 2005 WK with the Hemi option. No fuss, no muss, but it will set you back around $38,000 (MSRP). If budget is a concern, used Hemi Grand Cherokees will probably be selling for around $20,000-$24,000 in about three years.