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June 2013 Techline - 4x4 Questions

Turbochargers
Ali Mansour
| Brand Manager, 4WD & Sport Utility
Posted June 1, 2013

Your Tech Questions Answered

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.

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