Top 25 Most Asked Jeep Tech Questions
The Questions That Haunt Us Monthly
Sometimes it gets a bit comical. We get dozens of emails every day asking nearly the same thing: "What gears should I run?"; " Why is my speedometer off?"; "What size tires can I fit?" You get the idea. Sometime we'll get two or three identical question back-to-back. It's almost like somebody out there is messing with us. So to up the sanity level just a tad, we compiled the top 25 tech questions we are answering over and over again.
QI just installed XYZ-sized tires and now my Jeep is a dog. What gear ratio should I run?
A There are a lot of variables, such as your engine type and size, manual or automatic transmission, overdrive or not, driving style, vehicle's primary use, and so on. For starters, you've got to keep in mind that a smaller four-cylinder engine will require more gearing to regain the performance and loss of drivability incurred with larger tires than a larger engine making more power. Also, an automatic transmission without a lockup torque converter will allow the engine to spin roughly 100-150 rpm higher than the same setup with a manual transmission or an automatic with a lockup converter due to slippage in the torque converter. With those caveats, take a look at the chart below for a few general gearing guidelines that have worked well for us in the past.
Q My AX-5 is grinding and needs to be rebuilt or replaced. What do you suggest?
A The AX-5 found behind 2.5L four-cylinder engines is okay at best. However, we can't see ourselves ever rebuilding one, so it's hard to recommend our readers do the same. Instead, we'd look into replacing the little five-speed with an AX-15 from a 4.0L YJ, TJ, or XJ with an Advance Adapters conversion kit. You'll also need to replace the input gear on the NP231 T-case to convert from the AX-5's 21-spline output gear to the AX-15's 23-spline gear.
Another option if most of your driving involves hardcore wheeling is to swap in an SM420 using a 60-degree V-6 bellhousing from a GM Camaro, S-10, or Blazer. The GM bellhousing will allow the SM420 to bolt up to the 2.5L. I'd use the factory GM slave cylinder, clutch fork, and throwout bearing. You'll need a conversion pilot bushing for the SM420's 0.590-inch pilot tip and a 10-spline clutch disc. Or, if you don't want to scrounge junkyard parts, you can use a Novak Adapters PN B150GM to bolt the tranny to the engine. There are several different types of adapters available to convert the SM420 to the Dana 300/NP231 pattern T-case. Although you'll loose the overdrive, if you do a lot of off-roading, the 7.05:1 First gear of the SM420 offers a huge increase in slow-speed gearing compared with the AX-5's 3.93:1 First gear.
|Engine||Tire Size||Suggested Axle Ratios for Specific Transmissions|
|(diameter, in)||3-spd. Auto||4-spd Manual||Overdrive|
Steer Clear Rear
Q I've got a Dana 20 rear axle and want to build it for off-roading with big tires. What do you suggest?
A For starters, a Dana 20 is a transfer case used in late '60s to late '70s Jeep vehicles. A Model 20 is a rear axle put in full-size Jeeps and CJs from the mid-'70s until the early '90s.
There's really nothing wrong with the Model 20 that came in full-size Jeeps. These axles used heavier axletubes and good one-piece axleshafts.
While the CJ Model 20 used the same 8.875-inch ring gear and 29-spline carrier as the full-size Jeep, these axles have relatively weak axle tubes that are prone to flexing and bending with heavy use. Furthermore, the casting where the tube enters the centersection is comparably weak and has been known to crack and fail and/or the tubes can spin in the centersection bores, allowing the pinion to shoot straight up at the floorboards. Finally, the CJs were given a horrendous two-piece axleshaft setup that used a nut and Woodruff key to attach the hub to the shaft. In the field, the nut could back off and/or the Woodruff key could shear, effectively ruining your day.
We'd recommend adding some one-piece conversion shafts and hitting mild trails with 31- or 32-inch tires and a limited slip. But if you're thinking of punishing your CJ Model 20 off-road with 33s or larger tires, we'd put our money into a Dana 44, Ford 9-inch, Dana 60, or some other beefy axle swap.
Although there are a number of one-piece conversion shaft kits on the market, it's really a waste of money if heavy wheeling is in the axle's future. Because of the tube flex, axle seal life is shortened, leading to leaks. And centersection cracks and bent tubes are likely with big tires and heavy off-road use.
No Stink Link
Q What's with the high cost of TJ/JK lift kits? It's just a couple springs and some bushing ends welded onto some tubing, right? How much do I really need to spend to get a good lift?
A Aside from all the money the company is trying to recoup from its research, development, and design stages when producing a quality suspension system, a surprising amount of steel and manufacturing effort goes into a good suspension system.
It's old news by now, but the price of steel has pretty much doubled over the past couple years and it only seems to keep going up. Most of the name-brand suspension companies don't skimp on the quality or quantity of steel they spec for use in the springs and links. Skimping on spring materials and manufacturing will result in a suspension that sags after the first or second time off-road. Likewise, skimping on the control arm tubing thickness, diameter, and material can result in bent control arms. This can be true even if the arms aren't dragged over rocks. The control arms, especially the lower arms, have to contend with some crazy forces. And because of leverage, the longer the arm, the more force is exerted on the tubing. That's why you see long-arm suspension systems that use heavy-wall tubing on the lower control arms. It's pretty standard for 0.188-wall and even 0.250-wall tubing to be used since 0.120-wall and thinner can fold.
What do you really need? Look for components like adjustable upper control arms so you can dial in the pinion angle, adjustable track bars and reinforced track bar brackets, monotube shocks, progressive-rate coils, and any necessary steering correction components like dropped pitman arms and track bar relocation brackets. And don't forget the small stuff like longer brake lines and plan on getting a front-end alignment to adjust the toe settings and center the steering wheel.
Q I want to install some tires on my Jeep that will give me good off-road performance in the mud and rocks, but that won't wear out too fast. I can't afford to be putting a new set of tires on my Jeep every other year.
A Well, get cozy with the phrase "There's no free lunch," because the generous tire voids and large, aggressive lugs that make a tire work well in the mud and rocks often lead to quicker tire wear.
Many modern mud terrain tires feature computer-designed tread patterns that not only evacuate mud and water efficiently, but incorporate small grooves or siping on the tread blocks that allow more tread flex on the road and more biting edges in the rocks. The increased on-road flex allows longer wear and increased tire life. Bottom line? Your chances of mixing longevity and performance are better with a newer, more modern tire design as opposed to some of the old standbys.
Q I want to lift my XYZ Jeep XYZ inches. Will I need to install a CV rear driveshaft?
A This is one of those questions for which the answer can vary on a case-by-case basis, but there are some general rules of thumb. Remember, vehicles with longer factory rear driveshafts can get away with more lift before a double cardan (commonly referred to as a CV) shaft is needed. Assuming the drivetrain is left in the stock position, meaning the engine is not raised and the transfer case is not dropped, here are some general rules of thumb governing at which lift heights a double cardan rear driveshaft becomes a necessity.
JK: Over 3 inches (2 door);over 4 inches (4 door)
Wrangler: Over 3 inches (TJ/YJ); Over 4.5 inches (Wrangler Unlimited TJ)
XJ: Over 3.5 inches
Flattie/CJ-5: Over 2.5 inches
CJ-7: Over 3 inches
FSJ Wagoneer/Cherokee: Over 6 inches
FSJ Pickup: Over 8 inches
Q I've been trying to remove the stub shafts from my Dana 30's Unitbearing with no luck. What's the trick?
A Even down here in the southwest were it never snows and hardly ever rains, separating the stub shaft from a Dana 30 Unitbearing can be a chore. The problem is compounded by the fact that in order to prevent vibration, the shaft's splines engage into the unit bearing with a rather tight press fit. Throw in years of rust and corrosion and you'd better be prepared for a fight when trying to dismantle some of these assemblies.
Your best method will involve a lot of time, patience, and penetrating lube. There are a lot of good ones out there, but you'll have to get a bit more serious than WD-40. We've had excellent results using Justice Brothers JB-80 (justicebrothers.com) and Federal Process Corporation's Free All (federalprocess.com).
Soak the nut and the shaft splines before starting. You may need to go as long as a week, reapplying the lube once or twice per day. If the nut hasn't rusted away, an impact gun will be your best bet for freeing the nut. Otherwise, go for a long breaker bar and give it hell. If the edges of the nut have rusted away, you could try a pair of channel locks or even Vise Grip pliers, but don't hold out hope for either working. Chances are you'll be carefully MIG or TIG welding a new nut onto the stripped, rounded one.
Once you get the nut off, either use an air hammer with a blunt bit to free the stub shaft from the unit bearing or thread the shaft nut back on a few turns to protect the stub shaft threads and whack away with a heavy dead-blow hammer. Resist the urge to use a steel sledge, as it will likely result in serious shaft, bearing, or hub damage. And don't break out the torch. Aside from the fact all that penetrating lube will go up like a Roman candle, you'll probably waste the bearing's grease and seals.
Q I recently put larger tires on my Jeep and now I've got serious death wobble on the street.
A When trying to diagnose death wobble, always start small and work your way up. Although the larger tires may seem like the cause of the problem, in reality they are often only making an already existing problem noticeable. Start by checking the front wheel bearings. Simply jack the front tires up off the ground and, grabbing the top and bottom of the tire tread, try to wiggle the tire/rim back and forth. If any lateral play is noticed, check to see where it's coming from. The usual suspects are the hub bearing preload (or the Unitbearings on newer Jeep vehicles) or the ball joints.
If the hub adjustment, bearings, and ball joints check out okay, move on to the tires, making sure they're properly balanced. You can try mounting the rear tires on the front and see if that helps. If not, take the tires back to the shop that did the balancing and have them make sure the balance is still true.
With the tires ruled out, move on to the steering linkage tie rods and/or rod ends. Check the tie rod ends, drag link ends, and the track bar bushings (if applicable), as any one or combination of these can contribute to death wobble.
Finally, if your Jeep has been lifted, check the front axle caster. You generally want 4-6 degrees positive caster (bottom ball joint in front of top). Usually when a lift is installed the front axle may be rotated upwards to alleviate pinion angle and reduce driveshaft vibration. However, when the pinion is raised, caster is lowered. If your caster is too low, remove or replace the spring shims if your Jeep has leaf springs, or adjust the control arm length or (if applicable) the eccentric bolts to increase caster to the desired amount.
Q I recently installed bigger tires/different gears and now my speedometer isn't accurate.
A It's simple math, but if you increase your tire size by 10 percent, your speedometer will read slower by 10 percent. If you increase your gear ratio by 10 percent, your speedometer will read 10 percent faster. Whichever modification you're working with, there are a few methods of correcting your speedometer no matter what year Jeep you have.
Older Jeeps with mechanical speedometers will need to run a drive joint with a specific ratio to either slow down or speed up the speedometer. The drive joint mounts in between the transfer case speedometer gear drive and the speedometer cable and is currently offered by Stewart Warner (stewartwarner.com).
Jeeps from the '70- to mid '90s that run fully mechanical or mechanically-driven electronic speedometers can have new speedometer drive gears installed into the transfer case tail housing. Replacement gears with 26-38 teeth are available to correct for several ratios and tire size combinations. The gears are available through numerous distributors including 4 Wheel Drive Hardware (4wd.com) and Quadratec (quadratec.com).
Finally, vehicles with fully-electronic speedometers that use a Hall-effect pickup, and even mechanically-driven electronic speedometers, can use an electronic conversion box, such as the Superlift True Speed or the Jet Performance Speedometer Calibrator. Or there are a number of performance controllers and hand-held electronic programmer boxes that can adjust the speedometer readings by accessing the factory computer software through the OBD II port.
Q I want to swap a V-8 in my Jeep. Will I need to modify the firewall?
A This one always cracks us up because a V-8 swap involves so much work that modifying the firewall seems simple in comparison. Regardless, swapping a V-8 can generally be done in any Jeep without firewall modifications.
About the tightest and most common swap is sticking a small-block Chevy into a flatfender. The two biggest factors in fitting everything in the stock location is the large distributor cap on the factory Chevy HEI distributor and the more common long water pump assembly. Swapping to a short water pump and accessory package and swapping out to an aftermarket small cap electronic ignition distributor will allow you to just squeak a SBC under the factory flattie hood.
For an even cleaner swap, we'd consider a small-block Ford, a Buick V-6 or V-8, or even an AMC engine. All of these designs have front-mounted distributors that will allow the engine to be positioned a little farther back in the engine compartment without firewall interference.
Q I use my Jeep mostly for commuting, but hit the trails about one weekend every month. Should I buy an all terrain or mud terrain tire?
A There's really too much personal preference involved in a loaded question like this. However, although you'll almost always get more mileage out of a set of all terrain tires, manufacturers nowadays are employing some pretty advanced computer designs to create moderately aggressive mud tires that are quiet and that roll smoothly on the street. While you won't get the animal traction of a gnarly Interco Swamper or BFG Krawler, a mild mud tire such as the Toyo Open Country MT or the Pro Comp Xtreme Mud Terrain will get the job done off-road without wiping out your ear drums on the street.
Q What do I need to convert my early Jeep from drum brakes to disc?
A No matter how much we cover this question in the magazine and on our website, we always seem to get asked about converting drum brake axles to disc. For starters, visit jpmagazine.com and check out the story, "Early Jeep Disc Brake Conversion-Timeless Tech Drum to Disc" by former Jp staffer Verne Simons.
Early Jeep Dana 25, Dana 27, Dana 30, and Dana 44 axles originally equipped with drum brakes share the same round six-bolt spindle and backing plate bolt pattern as later GM, Ford, and Dodge Dana 44 disc brake axles. So, it stands to reason that you can use some combination of these parts to convert to disc brakes. For the story, Simons used the following: calipers from a '71-'78 Chevy 1/2-ton or light-duty 3/4-ton 4x4 with a Dana 44, caliper mounting brackets from a '73-'91 1/2-ton Chevy 4x4, Rotors from a '77-'78 CJ (These rotors are 11/8-inch thick), ten longer wheel studs (he used Dorman PN 610106), Chevy 1/2-ton brake lines (Pro Comp PN 7220), a grinder, standard hand tools, brake fluid, new hard brake line, banjo bolts, and a bleeder kit.
You may be able to do the same swap on the rear Dana axle providing it has the same round six-bolt backing plate pattern as the front.
Q I've been considering performing a shackle reversal for a better on-road ride. Is it really worth it?
A The on-road ride comparison between a shackle-reversal suspension and the standard factory shackle-forward design is like night and day. But that's not to say that either is without its own set of advantages and disadvantages.
Although positioning the shackles at the rear of the spring pack in a shackle reversal allows for a more natural compression of the spring as the front axle travels upward and back, it can be argued that it doesn't offer as much traction to the front tires when off-road. In the standard shackle-forward configuration as the tire starts to climb an obstacle and the springs compress, the tire is forced forward into the obstacle, increasing bite. However, having driven both suspension types off-road, we'd say we haven't really noticed any measurable difference in off-road performance. But the on-road ride is way better with the reversal.
Too Slow to Four-Oh
Q I've got a 2.5L Wrangler and want to swap in a 4.0L. Is this a bolt-in swap?
A For the umpteenth time, if you want a 4.0L Wrangler it's cheaper and easier to sell your 2.5L and just buy the Jeep you want. Even if you've loaded your 2.5L with a bunch of modifications, it still makes sense. Regardless, let's run through the mechanics of it all.
For starters, you can't just bolt in a 4.0L to the AX-5 that originally backed the 2.5L. Aside from the fact that the two engines have different bellhousing bolt patterns, the AX-5 doesn't have a prayer of lasting more than a couple hundred miles with the power and torque of the 4.0L. So, you can automatically add a transmission swap into the mix as well. Oh, and you'll need to take the NP231 T-case apart to install a 23-spline input gear since the 2.5L Jeeps have a 21-spline input gear. Add that to the pile.
Then, there's the sundries that everybody seems to forget about. Since the 4.0L is longer than the 2.5L even if you put the 2.5L's accessories onto the 4.0L's brackets you'll need new power steering hoses, radiator hoses, heater hoses, and a new fan shroud. Don't forget that you'll need to lengthen the fuel lines to reach the 4.0L manifold, do a new exhaust forward of the catalytic converter, and install new engine brackets on the frame. Then you'll need to lengthen pretty much every sensor wire as well as the charging system wires and then plop in a new 4.0L factory computer and add the harness connectors for the extra two injectors. Man! Now, consider that you can pick up a decent 4.0L TJ for well under $5,000 or a clean 4.0L YJ for $3,000 or less and it doesn't make a whole lot of sense to go through all of the above. Does it?
Man Oh Manifold
Q I read that swapping to a '99-up intake manifold will get me 20hp. Is this a bolt-on deal?
A Don't you think if the swoopier U-shape of the '99-up manifold added that much power over the older square-shaped 4.0L manifold (shown) the factory would've claimed that in its marketing? We've done a fair amount of dyno testing with 4.0L Jeeps and, aside from a 10hp difference either way, there's usually not that much variation between the baseline numbers generated by stock H.O. 4.0L Jeeps from '91-'06. They all put down right around 135-150hp at the tires.
However, if you still want to swap to the later manifold, you'll need the '96-up power steering bracket and will need to lengthen some of the sensor wires. The fuel rail should work. Be warned, however, Trasborg did the swap and actually lost power on the dyno with his '97 XJ, so unless you're adding a turbocharger or other big power adders, the log-style manifold seems to be a better match to the '98-earlier head and camshaft profile.
Q What parts do I need to put a 4.0L head on the 4.2L?
A The H.O. 4.0L head found on '91-'06 TJs, XJs, ZJs, and WJs is drastically better than the factory head found on 232 and 258 engines.
Hesco (hescosc.com) offers a kit under PN HES4240CHC that includes a modified H.O. 4.0L head for use with the 4.2L block, gaskets, and a valve cover. You'll still need to obtain a 4.0L exhaust manifold or header.
If you choose to go the low-buck junkyard route, you'll need to fill in some of the water passages on the 4.0L head with epoxy or JB Weld. Most machine shops we've spoken with recommend using water-soluble packing peanuts. You shove the peanuts into the hole, leaving roughly 1/2- to 1/4-inch of room for the epoxy. Then fill it up and grind it smooth. The peanuts will dissolve into the coolant and won't affect flow within the engine.
The coolant passages that need filling will be evident, when you compare the 4.0L head to the 4.2L block, but they're on the intake side and flank the head bolt holes.
Forcing the Induction Issue
Q I'm considering adding either a supercharger or a turbo system to my 2.5L/4.0L for more power. Is one better than the other?
A Both a supercharger and a turbocharger do the same thing. They compress the air from the atmospheric pressure of 14.7-psi at (sea level), allowing the engine to ingest more air than it could when naturally aspirated and thereby allowing a proportionate amount of fuel to be introduced to the engine. It basically makes the engine think it's bigger than it is.
However, the way in which each accomplishes this compression differs. A supercharger is driven off the crankshaft of the engine. Since it's mechanically driven, it contributes a bit to the overall parasitic power losses the engine incurs. A turbo, on the other hand uses the flow of exhaust gasses to spin the compressor. Although it's not exactly free power, a turbo doesn't accrue the same parasitic losses as a supercharger. Both methods require some form of intercooler to realize their full potential since the intercooler will combat the inescapable byproduct of compressing air - heat.
That said, at the modest boost levels of 4- to 7-psi that most Jeep forced induction systems run, these differences between turbocharging and supercharging are minimized. Furthermore, the aftermarket is very adept at matching turbo sizes to their intended aftermarket application to do away with excess turbo lag and decreased drivability.
Which do we prefer? Based on its sheer capacity for power building, we'd be more inclined to go turbo. In the Jeep world, 505 Performance (505performance.com) has some pretty complete kits whipped up that make some real power. Just check our recent Insane Inline series that made an astounding 693 hp with a 5.0L stroker inline-six. On the other hand, supercharger companies like Avenger Superchargers (avengersuperchargers.com) and Adventure Innovations (adventure-innovations.com) both have very complete, well-designed supercharger kits for Jeeps. In the end, it's up to you to pick your own poison.
Q My Jeep has a 4:1 gearset in the transfer case and an automatic transmission. When I'm off-road in low range I have to step on the pedal with both feet to get the Jeep stopped. What can I do to get my Jeep to stop off-road?
A This is the definition of the axiom, there's no free lunch. All that awesome torque multiplication and off-idle chugability that keeps you going forward through gnarly rocks can quickly overcome even the stock four-wheel disc brake setup on a modern Rubicon.
For starters, it's probably a good idea to swap to stickier brake pads. The stock pads are geared more towards longevity than brute stopping power. Check EBC Brakes (ebcbrakes.com) for some stock replacement pads that will really put the hurtin' on forward momentum.
However, I'm sure the pads aren't going to solve all your problems. Some of the guys at Jp have had moderate success with hydroboost setups, which do away with the vacuum booster and replace it with a hydraulic booster powered off of the power steering pump. Or, replacing the stock master cylinder with an aftermarket unit with a larger 11/8-inch bore master cylinder and a dual-diaphragm booster with an adjustable pushrod such as the one pictured from Dave's Customs Unlimited (davescustomsunlimited.com) will get you good results with the stock calipers.
Just a Yoke
Q My Jeep needs a slip yoke eliminator. Should I take it to a shop or try to do it myself? How hard of a job is it really?
A While we wouldn't recommend it for the novice wrench, if you can do a brake job or fix a broken front axle shaft in the field, we'd wager you could tackle a slip yoke eliminator install.
Really, the hardest part is getting the case halves separated. Most slip yoke eliminator kits include detailed directions, but here's a quick and dirty rundown just to give you an idea. Start by removing the front and rear driveshafts followed by the front and rear output yokes and the speedo cable or wires. Drain the fluid and then remove the bolts holding the tailshaft housing on. You'll need to take off some snap rings from the rear output shaft, then you can remove the output housing and remove the case half bolts. Then, gently yet firmly pry the case halves apart.
Grab the output and input shafts and move them to the bench, complete with the chain. Leave the low-range gearset and shifter in the case. Remove a couple snap rings and transfer the components from the old mainshaft over to the replacement shaft. Then, stick it all back together and bolt it up. You've got to make sure the oil pump feed tube doesn't come off of the pump when you're putting everything back together.
Q I'm going to swap to a Ford 8.8/Ford 9-inch/etc. axle eventually, but until then what can I do to make my Dana 35 survive?
A Listen people. The Dana 35 is a turd. It just is. We just can't polish it up any more than that. If you want to make it last off-road, then don't put a locker in it. With a locker, we've really seen them break behind a 2.5L running 31x10.50s. Leaving it with an open differential is one of the only things you can do that will stretch its life off-road.
In reality, by the time you get done adding an aftermarket set of 30-spline shafts, a new 30-spline carrier, a truss, and gearing it, you're perilously close to the cost of a good aftermarket 9-inch or Dana 44.
JK Axle Info
Q I put a small lift and 37s on my JK, but now my front axle looks bent. The tops of the tires point inwards towards each other.
A In reality, we doubt you really bent your axle. That's not to say it's not straight. But every JK Dana 30 and Dana 44 front axle we've come across has seemed to have noticeable negative camber. We don't know if the factory sets the up that way for some reason or if it's just from the heat of welding on the coil buckets.
But you're not quite out of the woods. While the internals of the JK axle are very good, the front axletubes are as notoriously weak as the previous Wrangler axles. For the permanent solution to bending, Dynatrac (dynatrac.com) has heavy-duty replacement front axlehousings. Or, you could visit Off Road Evolution (offroadevolution.com) to check out the company's affordable axletube sleeves and gussets that you can weld to your JK axle to bolster its strength. However, this isn't going to help if your axle is already bent.
Q I'm ready to add a winch to the front of my Jeep. Should I pop the big dollars for a Warn or Ramsey, or go with one of the cheapie winches I see advertised online?
A There's something to be said for quality. And if you're hanging your entire Jeep's weight from a winch going up a waterfall the last thing you want to hear is cracking plastic and bending metal. And you certainly don't want to smell fried solenoids and wiring during long, hard slogs through thick, gooey mud. If gnarly wheeling is in your future, if you do long pulls through heavy terrain like mud, snow, or rocks, or if you plan on pulling vehicles larger than your own, then we'd say going with a big name winch is a wise investment.
If you only wheel occasionally and you're just looking to stick something on the front of your Jeep in the rare occurrence you get stuck, then you should check out our story, "Affordable Winch Review" online at jpmagazine.com for some more information on winches that will set you back less than $650.
Q How can I eke a little more mileage out of my 4.0L?
A Believe it or not, you can usually make a 4.0L get mileage just as good, if not better than a 2.5L. Remember, you usually drive a 2.5L with your foot on the floor.
For starters, run a couple bottles of fuel injection cleaner through your fuel tank to rid your injectors of any deposits. Then, a cold air intake will really help flow at mid- and full-throttle and by itself can be worth 1-2 mpg. The stock 4.0L ignition doesn't need much help to light off the mixture, but it's still a good idea to check the cap, rotor, and plug condition and replace them if necessary. A good free-flowing after-cat exhaust and even a header will noticeably bump up the power and help with the mileage. Finally, if it's a Wrangler, consider replacing the factory fixed-blade fan with an electric fan. On a stock Jeep with all of the modifications listed above you could see as much as a 3mpg increase.
Q What's the best lift kit for my Jeep?
A "Whichever damn one you want." Or at least, that's usually our first thought. Whether leaf spring, coil, simple, or full mambo, you owe it to yourself to do a little research. The Web is your friend. Virtually every manufacturer is marketing its suspensions on its web sites. Pick your lift height, then pick your budget, then do your research.
Start by comparing the components included in each manufacturer's systems. You're looking for steering corrections, dropped brake lines, methods of driveshaft angle alleviation, and so on. The one with the most complete kit is usually the winner. Once you narrow down your selection to just a couple, then shoot me an e-mail, post up to the Q&A section on jpmagazine.com, or even ask at your local off-road shop.
Q Spring-over or spring-under? Which is better?
A couple years ago we were actually making fun of guys with spring-under suspension. Well, maybe not making fun. But we certainly didn't hold them in as high regard as guys running spring-over.
Our tune has significantly changed. With all of the excellent spring packs made today, we can't really see much of a need to go spring-over unless you're trying to go total junkyard. It opens up a whole can of worms with regard to steering corrections and axle wrap issues. We're fairly certain we've done our last spring-over conversion for at least the next decade.