Your Top 4x4 and Off-Road Tech Questions Answered HerePosted in How To: Tech Qa on February 1, 2019
GM Small-Block SwapWhy don’t you see more L31 Chevy small-block V-8 engines used for budget swaps?
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The GM 5.7L L31 V-8 was based on the original GM small-block, which was first offered in 1955. The truth is that many people are convinced that the LS engines are a better swap, although in most cases this is not true for an off-road rig. Unfortunately, the older GM L31 Vortec engine swaps kind of already ran their course prior to the mid-’00s. Today, the newer GM LS engines receive the most attention, and rightfully so. The LS is much easier to modify to make a ton of horsepower, and the aftermarket is flush with bolt-on parts that do just that. This makes it a great competition engine. Unfortunately, off-road enthusiasts just don’t need the kind of high-rpm power that the LS is best at producing. True trail rigs and most off-road vehicles in general benefit from low-rpm grunt. This is where the Vortec GM V-8 really shines in stock form or when properly modified.
The GM LS V-8, while a great powerplant for high-rpm mud whomping and dune blasting, can be a delicate and finicky engine in an off-road trail rig. The tight tolerances and the thin oil the engine requires can make the powerful LS engine unhappy at odd angles off-road. With the wrong oil pan, the LS will starve for lubrication and eat itself much more quickly and easily than any tried-and-true GM small-block, including the L31. If you perform an LS swap on your 4x4, it is imperative that you use the truck oil pan and a windage tray or a dry sump system to avoid oil starvation issues at angles. If you only race around town and on gravel roads, pretty much any LS oil pan will likely work fine.
Another reason you see fewer GM 5.7L L31 swaps today is availability. Most wrecking yards are filled with vehicles that are 20 years old or younger. The once popular L31 engine can be found under the hood of ’96-’02 GM vehicles. It was replaced by the 5.3L LM7 in ’03 GM vehicles. That puts the L31 near the tail end of its junkyard lifespan, where the 6.0L and other desirable LS truck and car engines are at their peak.
Having said all of that, the L31 is still a great engine choice for swapping today. New L31 HD crate engines are available from companies like Pace Performance (paceperformance.com) and Summit Racing (summitracing.com) under GM part number 12530283. It is an all-new engine from oil pan to valve covers. It features Vortec-style cast-iron cylinder heads, a one-piece rear main seal, hydraulic roller lifters, center-style valve cover hold downs, and four-bolt main bearing caps. It’s designed to be a direct replacement engine for ’96-’02 L31-equipped vehicles and GM provides a limited 3-year/100,000 mile parts and labor warranty. Of course, you’ll have to add on your intake, ignition, fuel injection system, exhaust manifolds or headers, and front accessory group.
Brake FlaringWhat is the best tool/technique for flaring brake lines?
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There are a lot of brake line flaring tools out there that simply don’t work very well. If it’s a cheap tool, you can pretty much assume it won’t work well. This is one area where we recommend purchasing a high-quality tool. You’ll save yourself a lot of headaches and wasted tubing. We’ve been really happy with the Mastercool (mastercool.com) hydraulic flaring tool. It comes in several different versions. You can order it as a full-tilt kit with the flare types you use most, and you can purchase separate flare adapters if you need them later on down the road. Flaring the brake lines with the Mastercool flaring tool is easy. Initially, you’ll feel like you want to really squeeze down on the hydraulic lever when flaring. This isn’t necessary. It creates an overly fat male flare that won’t fit in the female fittings. It takes a little practice, but you quickly learn to not overflare the tubing. The tool can also be used to create a bead on metal tubing for use with rubber hose and a worm clamp.
Ramcharger RewireWhat’s the easiest wiring harness you’ve used to rewire an old 4x4? My ’75 Dodge Ramcharger needs a new wiring harness bad. I’m tired of fixing something on every trip.
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If the plugs and connectors in your Ramcharger are in bad shape, you may need to try and find a good used harness. If your plugs and connectors are useable, you have some options. If you have more time than money, you should be able to go through the entire harness and find the bad spots. Repair anything that looks chaffed, burnt, or hacked into.
The second option is to go with one of the many different universal wiring harnesses available. Companies such as Painless Performance (painlessperformance.com), Kwik Wire (kwikwire.com), and Rebel Wire (rebelwire.com) offer universal wiring harnesses that can be adapted to your Ramcharger.
The third option is to install a reconditioned factory wiring harness from Brad’s NOS Parts (bradsnosmopar.com). The company can supply you with a reconditioned factory wiring harness that has been cleaned, tested, and taped to work like new. All of the harnesses feature the correct factory connectors and terminals for a direct replacement.
Blame AMCWhy do the front axles under most 4x4s have a driver-side differential?
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The reason for the differential location is actually a lot less glamorous than you might think. Interestingly enough, most front differentials didn’t start out on the driver side. Many older 4x4s such as Dodges, GMs, Jeeps, and Toyotas have a passenger-drop front axle. It wasn’t until later that they switched, matching the driver-side differential drop of the Ford 4x4s. It just so happens that the switch was around the same time as the industrywide changeover to chain-driven transfer cases in place of gear-driven units. In most cases, the differential location is dictated by packaging and available clearance in a chassis. In other cases, however, vehicle-manufacturing budgets appear to have come into play.
We reached out to retired Jeep old timers Phil Toney and Mike Smith to get a firsthand story. The reason for the differential location change that Jeep made from the passenger side on the CJ in 1986 to the driver side on the YJ Wrangler in 1987 might surprise you.
“With the left-side differential, the engine is offset slightly to the right, so there is better side-to-side weight balance with a driver behind the wheel than with the right-side differential. One problem we had with the right-side differential was with V-8 CJs, where under vigorous driving the right-side differential would hit the V-8 oil filter/pump, causing loss of oil pressure and possible engine failure. A cross-frame brace was added, which helped reduce engine movement. Other considerations were packaging, Quadra-Trac transfer case usage, and so on. Historically, differentials were on the right side, but the move to NP transfer cases with YJ drove the differential to the left side.”
“For the ’80 model year, there was a joint program to develop a new transfer case for the Jeep Wagoneer and Cherokee, plus develop the new AMC Eagle. The packaging of the front axle on the Eagle required the differential to be on the driver side. In order to justify the cost of developing the Eagle, it was decided to use a common NP transfer case. The NP119 model was used in the Eagle and the NP219 model with low range was used in the senior Jeep line. When they incorporated two-wheel drive in 1981, the numbers changed to the NP129 for the Eagle and NP229 for the Jeep. This forced the Jeep to change the differential to the left side. When the CJ went out of production in 1985 and the YJ went into production in 1987, the Dana model 300 transfer case used in the CJ with the right-side front axle was no longer available. The YJ was forced to use the New Process transfer case. Thus, the reason for the difference between the CJ and YJ front axles. It was purely for packaging.
As an aside, there were budget constraints during the time of the development of the Eagle. Jeep had a generous budget, but the passenger-car group had a lean budget. Therefore, in order to justify the Eagle, it was necessary to hide much of the cost in the Jeep budget. That of course included the new transfer case, which was the highest-cost item, and a change to the front axle on the Jeep to accommodate it. We could have developed an NP transfer case to accommodate the right-side front axle on the Jeep far cheaper than the tear-up required to change to a left-side front axle. That’s just how things work. So, the bottom line as to why the Wrangler has the differential on the left side is because of the AMC Eagle.”
Bed CompressorI want to put an onboard air compressor kit under the bed floor of my truck, but I am concerned with road salt and freezing conditions here in the Northeast. Will the temperature range affect performance or cause any other concerns?
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Onboard air is an incredibly handy accessory to have on a 4x4, especially when coupled to a small 2- to 5-gallon tank. The compressed air can be used to refill tires at the end of a trail, reseat popped tire beads, inflate camp mattresses and lake floaties, or even run air tools for faster trail repairs. Unfortunately, as you may have found, real estate under the hood of many newer trucks is at a premium. There isn’t a lot of space for some of the larger high-performance air compressors. However, under the pickup bed, there is usually quite a bit of open space. The only caveat is that you’ll want to find a 12V air compressor that can handle the water and dirt it will no doubt encounter under there. Generally, if the compressor is designed to be mounted under the hood, it will survive under the bed just as well.
Something to keep in mind is that not all 12V electric air compressors are created equal. There are a couple of specification numbers you’ll want to pay close attention to when selecting an onboard air compressor. The first thing you’ll want to pay attention to is the cfm output. This is the cubic feet per minute that an air compressor produces. The cfm is usually given at a specific psi. For best results when airing up tires, look for a compressor with a cfm rating of at least 2 cfm at 30-40 psi, although 4 cfm would be more desirable. The compressor with a higher cfm rating at a given psi will ensure faster tire and air tank fill-ups. The cheapie low-buck air compressors will generally produce much less than 1 cfm at 30-40 psi.
The second number you should pay attention to is the duty cycle of an air compressor. Duty cycle is the number of minutes out of a 10-minute period a compressor can operate continuously. For example, if the 12V compressor has a duty cycle of 40 percent, it can run for four minutes before you need to shut it down and let it cool for six minutes. Published duty cycles are sometimes conservative, so you may be able to push the compressors a bit harder than advertised without damaging anything. Many of the 12V electric air compressors available have heat-protected circuits and will shut down automatically to protect the vitals from overeating. For heavy-duty use, companies such as ARB (arbusa.com) and Air Zenith (air-zenith.com) offer high-output 12V electric air compressors with 100 percent duty-cycle ratings, meaning you don’t need to let them cool down. The ARB Maximum Performance twin-motor compressor (part number CKMTA12) is sealed for moisture and dust resistance and has a 4.68 cfm rating at 29 psi. The Air Zenith OB2 compressor (part number AZOB2K) also features a moisture- and dust-resistant heavy-duty motor. It puts out 4.25 cfm at 30 psi. Either of these air compressors would be a great choice for the underside of a pickup bed. They both include removable air filters that can be extended elsewhere with a hose to ensure they only pull in dry, clean air.