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June 2013 Techline - 4x4 Questions

Posted in How To: Tech Qa on June 1, 2013 Comment (0)
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Why Turbo
I’ve noticed that many of the new cars, and some trucks, are coming with turbocharged engines from the factory these days. Do you know why more of them don’t use superchargers? It seems to me that the supercharger could deliver the same, if not more, power without the lag and all of the added complexity of a turbo.
Harrison Jenkins
Via email

The turbocharger vs. supercharger debate is an ongoing one in the tuner world. While it can be a complex topic, there are a few seemingly simple reasons that the OEs are more drawn to turbochargers as opposed to superchargers. First, it’s important to understand that both are basically performing the same task. Each works to increase the air being fed into the engine. The idea behind forced induction is that the more air that you can pack in, the more fuel you can burn. How the two differ greatly is where each sources energy.

Most superchargers are belt-driven. This belt rides on a pulley, which is often part of an accessory-drive loop that draws its power from the engines crankshaft. Since the crankshaft is the power source, the supercharger creates a more linear power feel when accelerating, whereas turbochargers are sometimes slower to spool, which creates that feeling of lag. While I agree that superchargers can be an easier packaging solution at times, they have one major negative in the eyes of the OEs.

Given that most superchargers draw energy from the crankshaft, it’s removing a certain about of power potential and efficiency from the engine. One of the biggest reasons that the turbocharger has surpassed the supercharger with the OEs is that it uses energy that would otherwise be wasted on a naturally aspirated engine. A turbocharger is fed by the heat and pressure that’s blasting from your vehicles exhaust. As the exhaust passes through the compressor wheel it spins a turbine shaft on the opposite side. This process causes the turbine wheel to increase the volume of air being fed into the engine. Since the turbo essentially uses wasted energy to create more power, it holds an edge over the supercharger.

Complex tuning, direct injection, variable vane, and compound turbocharging all continue to change the way we look at the turbocharger. Without question, superchargers still have a place in the OE and aftermarket sector. The fact is, though, that a turbocharger creates similar power gains with less energy draw. This makes them a better fit for OEs looking to capture more power and efficiency. A great example of this technology is the Ford F-150 EcoBoost V-6. It’s a twin-turbo six-cylinder that delivers V-8 power, while retaining V-6 fuel efficiency in most situations.

I recently read the “Low Cost Junkyard Engine Swaps” story in the August ’12 issue, and it got me thinking about my truck. I have a ’98 Chevy Silverado 1500 Z71 with over 150,000 miles. There is a misfire in the number-five cylinder. I would like to make it better on gas, yet still have a good amount of horsepower. Would it be better to rebuild it or just swap in a new engine?
Tristian Clendenen
Via email

With the exception of a turbocharged-diesel engine, trying to grab high horsepower and great fuel-economy numbers out of an older V-8 engine is an uphill battle. Swapping in a late-model V-8 engine would give you a bit more power and efficiency, but I doubt the fuel economy gains would be enough to justify the time and expense required for the swap. Rebuilding your V-8 will likely be the most inexpensive route. Assuming you don’t mind putting in a little time under the hood and have a good machine shop nearby, rebuilding your Chevy’s V-8 could be an affordable and fun learning experience. Depending on the type, a factory replacement engine can also be very cost-effective and most include some type of warranty.

Aggressive All-Terrains
I have been driving myself crazy trying to figure out what, for lack of a better term, aggressive all-terrain tires to buy. I have yet to find much of anything as far as professional reviews go, and the message boards are useless, as most posts are to the extreme. Examples of the tire style that I am referring to are the Kelly Safari TSR, Cooper Discoverer S/T MAXX, Pro Comp Xtreme A/T, Mastercraft Courser C/T, and Goodyear DuraTrac. These types of tires seem to be a mystery.

I think these tires would make for some good articles. Since most of my crew use their hunting trucks as daily drivers, it would be great to have a tire that performs decent off-road, but will last longer than most mud-terrains. My hunch is that most hunters don’t really need mud-terrains and the more aggressive all-terrains will fit the bill.
Courtney
Via email

Hybrid or “aggressive” all-terrain tires that you are referring to are widely popular these days. While the majority of 4x4 enthusiasts seem to prefer the appearance of a mud-terrain tire, many don’t necessarily all need the off-road benefits of the more aggressive mud cleats. The hybrid all-terrains like the ones you mentioned are part of a wave of tires that are working to bridge the gap between the traditional all-terrain and mud-terrain radial. These tires provide deeper tread blocks which tend to extended farther down the sidewall and increased spacing over a traditional all-terrain tire.

Collectively, the staff has tested nearly all of the aforementioned hybrid all-terrains, along with others such as the Falken WildPeak A/T and Mickey Thompson ATZ. As you have alluded to, some do work very well in the mud. I think a shootout between the modern-day all-terrains sounds like a great idea and will look into that more as time allows.

Gear Charting
I enjoyed reading your article “Ratio Right” in the March ’13 issue and have a question. You mentioned a “chart” when choosing the correct gear ratio in a 4X4. What chart and how do I get one? I have a ’13 Jeep Wrangler Rubicon with 4.10 gears and want to put 35s on it.
Tony Hahn
Via email

The type of chart I was referring to is similar to the gear ratio guide chart that can be found at www.4wheelparts.com. They are intended to calculate your RPM range given a certain tire size and gear ratio. None of them are perfect, as each application is a little different. For your ’13 Wrangler the 4.10:1 gears should be a good combo with 35s. A 4.56 ratio would give you a bit more pep, but I would try the 4.10s first and see if they fit your needs and wheeling style. You’ll also need a tire calibrator like the ProCal module offered from American Expedition Vehicles (www.aev-conversions.com). The ProCal module allows you to input the new gear ratio and tire size data. This will adjust your shift points (if you have an automatic transmission) and recalibrate the speedometer accordingly.

Tight Steering
I have a Jeep Cherokee XJ with a Currie 4½-inch short-arm lift and all of the company’s corresponding steering and sway bar components. Off-road it is plenty capable. Considering I drive it mostly on-road, the Jeep’s street manners and overall handing is very important. Currently, I really like how tight my steering and suspension feels, as there is little-to-no play in the wheel and no wander on the highway.

I remember driving my friend’s old and new Broncos in the ’90s, and as I recall they felt like they had a lot of play in the steering and suspension. I have been considering purchasing a classic Bronco and was wondering if upgraded with better steering and suspension components will it be as “tight” as something like my XJ. Or is this something I would only be able to find in a later-model vehicle?
Jeff Logandro
Via email

Steering and brakes are the two most important parts of any vehicle. If one doesn’t feel right or work correctly, it can be a bad day for a lot of people. Worn steering and suspension components, improper alignment, and bad tires can all play a role to make a steering system feel loose. Depending on what year of Bronco you are searching for, you will have few steering upgrade options. If you are considering a ’90s Bronco as a “classic,” then you will likely purchase one with a TTB (Twin-Traction Beam) frontend.

One thing that you may have experienced with your friends Bronco is the cycling of the TTB frontend. As the TTB cycles it pivots differently over the conventional solid-front axle like you have in your XJ. The TTB frontend is a type of independent suspension that uses axle beams connected at the center of the frame. As the suspension cycles, the wheels camber can change dramatically, depending on the amount of suspension travel. Desert-racers embrace the TTB, as it allows for tremendous vertical wheeltravel potential. On-road, the handling of a modified TTB Bronco may feel much different than your modified Cherokee. Can you make it feel tight and on-center? Sure. Will a TTB frontend feel the same as your solid-axle Cherokee? Not quite.

Driveline Brakes
I am building an ’85 Chevy ½-ton on 2½-ton Rockwell axles. I am in college and on a budget. I have been researching the brakes for it and I think I am going to go with driveline brakes. I found a couple of companies that make third-member brackets that will let me use Toyota calipers, which are pretty inexpensive. Are there any serious drawbacks to running this style of brake? I don’t drive my truck very long distances on the street, but it will be a street-driven truck, not a trailer queen!
Kyle Bartlett
Via email

I am actually in the process of examining the brake choices for my 2½-ton Rockwell project (Rescued Wrangler), so your email has great timing. Driveline or pinion-style brakes are an excellent option for the 2½-ton Rockwell axle. The 6.72:1 gear-reduction third member has plenty of strength to stop even a full-size Chevy such as yours and there are a fair amount of low-buck and high-end aftermarket brake options.

The main drawback of running a driveline brake versus a traditional outboard or wheel-mounted brake on the Rockwell axle is that the rotor is spinning 6.72 times faster than if was mounted outboard. This means if your wheel is rotating at 55 mph, your rotor is actually spinning at 370 mph! I don’t know of any Toyota calipers designed to stop a rotor spinning that fast. It wouldn’t take long for the heat created by the stopping force to warp the rotor. It just isn’t a safe idea for an on-road rig. I understand that the sticker shock of wheel-mounted disc brakes is a lot to take in, but if you plan to operate your truck on the street, it’s the safest option.

Slider Thoughts
I have a new-to-me ’08 Jeep Wrangler Unlimited. I am stoked on the Jeep and excited about wheeling it more. It currently doesn’t have any kind of body armor or sliders. After researching the topic on multiple forums, it seems like a lot of guys use body-mounted armor, while only some use frame-mounted sliders. I don’t want to tear up the body or buy the wrong armor. Could you tell me the difference and what you would suggest?
Greg Pierce
Via email

Both armor types have pros and cons. Mounting armor directly to your rig’s body will offer more ground clearance and is often a bolt-on install. Body-mounted armor is often comprised of a thick-steel plate, but can sometimes be optioned in a lighter aluminum set. The main drawback of body-mounted armor is that the armor is usually tougher than the sheetmetal that it is mounted to. Continuous use on the trail and hard impacts can actually damage the body over time. I’ve witnessed a few Wrangler Unlimited models come down hard on their body-mounted sliders, which caused a fair amount of damage to the surrounding body panels.

Frame-mounted sliders tend to work better at protecting the body as they are mounted below and separately from it. Typically, they are comprised of DOM tubing and are offered in both weld- and bolt-on configurations. While frame-mounted sliders tend to be more durable, they also typically absorb more ground clearance. Some companies such as EVO Manufacturing (www.evomfg.com) offer body-mounted armor and weld-on sliders that work independently from each other.

If you are looking to hit more hardcore trails and think your Jeep might be packing on the pounds with additional armor, I suggest frame-mounted sliders. If light-wheeling and a lightweight build plan are more in your future, then there are plenty of excellent body-mounted armor/slider combos such as the kind from Synergy Suspension (www.synergysuspension.com) and Poison Spyder Customs (www.poisonspyder.com) that work great.

Where To Write
Address your correspondence to: Four Wheeler, 831 S. Douglas St., El Segundo, CA 90245. All letters become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. The editorial department can also be reached through the website at www.fourwheeler.com. Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

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