Many Mods
How much power will I gain on my '04 LJ by installing the Edge Trail Jammer kit, a header, an after-cat exhaust, and a high-flow catalytic converter?
On a different subject, my Jeep has the Trac-Lok 4WD system in it. How does it work exactly, and will it mess the system up if I put a Trutrac in the rear?Farris ParkConway, Arkansas
Installing the complete Edge Trail Jammer package (cold air intake, bored throttle body, and electronic module) should get you almost 20hp at the rear tires. Honestly, I don't think you'd need the high-flow catalytic converter unless your factory unit is plugged up or rattling because the catalyst brick inside has come apart. And since it's an '04, I doubt either of these things has happened. You'll see a bigger boost in performance in going to an after-cat exhaust and ridding yourself of the restrictive factory 13/4-inch tailpipe. Gibson makes a nice unit that isn't obnoxiously loud, although you will hear the difference. Figure you can add another 5-10hp into the mix with the after-cat exhaust for a total of 25-30hp at the rear tires.
As for the "Trac-Lok" 4WD system, you're a little off on your vocabulary. For starters, your Jeep uses a "Command-Trac" 4WD system, which is just Jeep's fancy term for its NVG231 T-case. You've got 2WD High, 4WD High, Neutral, and 4WD Low. The 4WD system refers to the engine power distribution to the front or rear axles.
The Trac-Lok is a limited slip differential made by Dana Spicer that was an option in the rear axle. A standard open differential will send engine power to whichever axleshaft (and tire) has the least traction. This can cause loss of forward motion if a tire is lifted off the ground, is stuck in mud, and so on.
The limited slip differential sends engine power to both axleshafts (and thereby to both tires) at the same rate until a predetermined torque bias is reached, at which time the axleshafts may spin at different speeds. The tighter the differential, the greater the torque bias must be to overcome the differential action and allow one axleshaft to spin faster or slower than the other. The Trac-Lok is a relatively low-torque bias differential. It doesn't take much force to overcome the differential and allow one tire to spin at a different rate than the other. That's why they offer lackluster performance off-road compared with a differential with a higher torque bias, such as the Eaton Truetrac.
So, in my roundabout way, to answer your question, yes, you will realize better off-road performance by swapping out your factory Trac-Lok rear differential for a Truetrac. The Truetrac offers exceptional off-road performance for a limited slip with very civilized street manners.
Why Not Swap
I have a 130,000-mile '84 CJ-7 with a 4.2L, a four-speed, and Dana 300 T-case. I bought it two years ago with 129,480 on the odometer. It was completely stock with a shot suspension and little stock tires. The tires said something like P225/75R15 on them. I have put a lot of work into the Jeep, including a 4-inch Rough Country lift, 31x11.50-15 Super Swamper LTBs, 15x10 black steel wheels, reclining buckets out of a '91 S-10 Blazer, Herculined the inside, and changed the paint from a postal white to red. It looks really nice and everyone around loves this Jeep. I just so happen to have a '96 Dodge Ram 1500 pickup lying around with a good 318 in it. Which engine would you rather have; the 4.2L six-cylinder or the 5.2L V-8? I know it's a lot of work to swap, but I have everything but the adapter to connect the engine to the tranny. I would like to keep the four-speed and the Dana 300. The six-cylinder runs great, but with 130,000 on it, I know something is going to happen eventually. If I could just get your opinion, it would be greatly appreciated.Chris PoulinYork, Maine
Keep in mind that the Chrysler 318 is one of my all-time favorite engines. But with only 130K on the clock, I think you've still got a lot of life left in your 258. They're hard to kill. And if you're happy with the performance, maybe the engine swap can wait.
For starters, with only 31-inch tires you won't be stressing the drivetrain too much. However, if you do pull the trigger on the swap, you've got to consider a few things. Your '84 could have two possible manual four-speed transmissions : the T-18A (granny low 6.32:1 First) or the T-176 (3.82:1 First). If you've got the T-18A there's no need to worry, but the T-176 could have trouble with a V-8 and big tires. Technically, it should be fine since Jeep used them behind the factory 304 V-8, but it's not as burly as a T-18.
Second, the wiring harness will really need to be pared down on the Dodge's 318 and I'm not certain if the ECU will allow a manual transmission to be used if it was originally an auto. Most Mopar ECUs are linked to the tranny and unless they sense the signal from the lockup converter they'll throw a check engine light. Performance-wise it's nothing to really worry about, but it's an annoyance if you've got to have smog done in your area and would need to hook up a check engine light to get past a referee.
Don't forget about the electric fuel pump, high pressure lines, and return line to the tank for the MPI injection, hooking up the power steering, exhaust, and so on. All not too complicated, but folks tend to forget about the little stuff
I'd say you'd be really happy with a 318-powered CJ-7, but the time and effort you'd put into it could really turn the 4.2L six into a well-running machine. If your stock 258 has good compression and isn't leaking like a sieve, maybe consider a Howell injection system and electronic ignition for a small boost in power, mileage, and drivability. Chances are excellent that your 4.2L will last until at least 250K miles before needing any serious attention.
Got a tech question you're just itching to get answered? Send it on in to Jp magazine, Your Jeep, 6420 Wilshire Blvd., Los Angeles, CA 90048, or e-mail christian.hazel@jpmagazine.com.