Whoever coined the words, "Getting there is half the fun" obviously wasn't talking about hauling a racecar to the track. Whether the trip is made on back roads or an interstate highway, towing a trailered racecar is never fun, considering the countless brain-dead drivers you encounter along the way. It seems as though most of them think they absolutely have to be talking on their cell phones, drinking a cup of coffee, or both while they're careening down the highway.

The idiots to your right and left, and in front of you are never going to change, but if your tow vehicle has a bit more power, it may be easier to get away from them. As an added benefit, the power that helps you distance yourself from the accidents waiting to happen, also makes it easier for your rig to climb hills and get up to normal cruising speed. And although it may seem to be a contradiction, the same modifications that bring increased power, can also improve fuel economy.

Although the techniques used to improve the performance of different vehicles is similar, there are engine-specific differences. This month's edition of "Tow Story" deals with Chevy's Silverado and GMC's Sierra, virtually identical 1/2-ton pickups that are commonly used for daily transportation during the week and for hauling race cars on weekends. Since the 1999 model year, most of these trucks have been equipped with GM's 5.3-liter LSx "Gen3" small block. (GM's replacement for the old, reliable 350.) Rated at 285-315 hp depending on model year, the 5.3 delivers impressive performance. But when the weight a car, trailer, tools, tires, and spare parts are hung on the back, life in the fast lane gets a lot slower.

As is the case with a race engine, improved air flow and reduction of parasitic power losses are two important keys to improved truck engine performance. The relatively simple modifications we made to our 2002 Silverado test vehicle resulted in horsepower and torque readings of 268 and 308, increases of 24hp and 15 lb-ft of torque respectively. We didn't do individual tests after each modification, because we were trying to develop a "package" that would deliver significant improvements. We're also working on a towing-oriented heads/cam package for the 5.3. It will be covered in a future issue.

The horsepower increase we recorded is a bit deceiving and somewhat irrelevant, but it does put some of the advertised claims you may see into perspective. In a tow vehicle, peak horsepower is largely irrelevant because chances are pretty slim that you'll have the gas pedal on the floor, and the engine spinning at 5,500 rpm, when there's a trailer hooked to the rear; mid-range torque is of far more practical importance. As for the test numbers being deceiving, tests on a chassis dyno are typically done with the vehicle's transmission in "high" gear (with a 1:1 ratio) so that driveline losses are minimized. As is the case with many late model vehicles, the speed limiter in our test truck was set to 105 mph, which corresponds to an engine speed of approximately 4,500 rpm, well below the engine's 5,100 rpm power peak. That being the case, raising the speed limiter setting results in a sizable power gain, simply because maximum engine test rpm was increased.

One of the easiest methods of increasing both available horsepower and overall fuel economy is to replace the mechanical fan with an electric model. (This obviously applies only to engines equipped with mechanical fans; 2007 and later model GM trucks are factory equipped with electric fans.) Even though the stock fan is mounted to a viscous coupling, (that's supposed to allow the fan to free-wheel until engine temperature reaches a predetermined level) it still spins fast enough to consume a significant amount of power. The dramatic improvement in throttle response after the mechanical fan has been removed is further evidence of its negative impact on power-and fuel economy. Our 2002 Silverado test vehicle picked up a solid mile per gallon after its mechanical fan was replaced with a Spal dual electric fan assembly. In addition to a wide selection of fans, Spal also offers a unique pulse width modulated controller that allows easy setting of "fan-on" and "fan-off" temperatures.

Installation of an electric fan is not particularly difficult; removal of the original fan is a different story. The fan/coupling assembly mounts to the water pump pulley by way of a large nut that's virtually impossible to remove without the tool specially designed for the purpose. A 36mm open end (or adjustable) wrench and a big hammer will get the job done, but you'll save yourself a good bit of aggravation, and your knuckles a good bit of skin, if you buy or borrow the proper tool. After the fan is out of the way, the lower fan shroud can be removed and the electric fan assembly set in place. Since we used a "universal" type Spal dual-fan assembly, we had to fabricate the brackets required to mount it to the radiator support. The term "fabrication" is a bit of an over-statement-nothing more exotic than a few pieces of 1-inch wide aluminum, a vise and a drill are required to get the job done.

Setting up the fan's switch-on and switch-off temperatures using Spal's fan controller could be called "programming", but that would be another over-statement. All you have to do is press the "high" and "low" buttons on the controller when coolant temperature reaches the desired level and "programming" is completed. Unfortunately, the temperature sensor included with our controller was not of the proper metric persuasion required for installation in an LSx cylinder head, so we had to find one with the proper thread dimensions (available through most GM dealers, and many parts stores). If you can't find or don't particularly care about using a "genuine GM" sensor, BWD Automotive part number WT5132 is a suitable replacement.

A more direct route to increasing an engine's power output is to improve its breathing capability. That's easily accomplished through exhaust system modification. It's truly ironic that auto manufacturers spend so much time and money developing whisper-quiet exhaust systems, yet installation of aftermarket systems with a significantly more aggressive sound continues to be one of the most commonly made modifications. Although many aftermarket systems are installed in the quest for a "deep, throaty exhaust note," such systems also deliver increased power. That's largely because the same characteristics that restrict sound also restrict flow; within limits, increased flow capacity equates with increased power output.

Personal preferences vary greatly with respect to exhaust system configuration, so there are many "right" ways to modify a stock system. (Don't consider that statement as a license to do whatever is quick and easy-some modifications are just wrong.) The advantage of installing a complete exhaust system is that cutting and welding are not required. The disadvantage is expense. The original equipment systems used on 5.3-liter GM trucks incorporate mandrel bent 75mm tubing, so there's little to be gained by replacing pipes-it's the muffler that constitutes the major flow restriction. Aside from being large enough to house a small family, the stock muffler has enough internal twists and turns to confuse a seasoned navigator. That obviously creates a good deal of exhaust restriction-and that can be eliminated by replacing the stock muffler with a low restriction model.

Original equipment catalytic converters are another known power-reducing restriction. (The conditions under which a catalytic converter can be replaced are defined by both Federal and local laws, so be sure to check regulations before making modifications involving any emissions control device.) If your truck's converters need to be replaced, installing high flow models, such as those offered by Random Technology will pay off with increases of 8-10hp across the entire rpm range. GM's 5.3-liter engines are equipped with a Y-pipe that incorporates a converter for each cylinder bank. Replacement of the converters requires that the originals be cut from the Y-pipe and the replacements welded in their place.

One of the best ways to take full advantage of flow improvements made to an exhaust system is to make similar improvements to the intake system. Replacement of an original equipment air filter element with a low-restriction type is a no-brainer. However, a number of studies have shown that some brands of high performance air filters don't do a particularly good job of filtering. Issues seem to arise only under extremely dusty conditions, but it's a good idea to periodically check the intake ducting between the filter and the engine regardless of the air quality that normally surrounds your truck. Not only will you be able to determine whether the filter is performing satisfactorily, you'll also uncover any damage that is allowing unfiltered air to reach the engine.

Although the engine control systems used in late-model vehicles can adapt to a wide variety of mechanical changes, there are limits. Even within those limits, the systems are governed by relatively conservative factory settings that control air/fuel ratio, ignition timing, and transmission shift points. While typical bolt-on modifications don't require reprogramming of the vehicle ECM or PCM, (Engine Control Module or Powertrain Control Module) additional performance benefits can be achieved by doing so.

An obvious question related to reprogramming (or reflashing as it's commonly called) an ECM or PCM is, "If you can get better performance by changing some settings, why didn't the factory do it?" There are a number of reasons, but primarily because the factory has to consider the same type of brain-dead drivers that you encounter when towing to the races. You know the type-the guy who fills his tank with the cheapest low grade gasoline he can find, loads up the bed with a 1,000-plus pounds of whatever, and plants his right foot on the floor, while his truck struggles up a steep grade. It never occurs to these types of drivers that a gasoline engine shouldn't sound like a diesel, and they're always mystified when their engines or transmissions develop problems.

The best way to optimize ECM/PCM settings for your particular driving requirements is with a programming/scanning system such as EFILive's FlashScan. This system includes software, which will run on virtually any Windows-based computer, and the cabling necessary to connect a vehicle to a PC. The cable includes a "black box" which not only handles PC-to-vehicle communications, it can also serve as a stand-alone datalogging device.

FlashScan can be used to reprogram multiple ECMs/PCMs, so if you're inclined, you can improve the performance of other GM vehicles you or your friends own. On the other hand, there's a relatively steep learning curve associated with electronic engine controls and if you don't want to climb it, you can order a mail order tune, or have a professional tuner e-mail you a file that you can flash yourself, and use a learning tool.

Regardless of the method you select, your end goal is to optimize operating efficiency at the rpm and engine load levels that your truck encounters when it's hauling your racecar. Keep in mind that most control settings are contained in "maps"- two- and three-dimensional arrays with individual values associated with specific rpm levels and amount of engine load. Consequently, you don't have to be concerned that changes made to improve towing performance will have a negative impact when you're not pulling a trailer-or vice versa.

Ideally, reprogramming should be done after all other modifications are made, but in the real world, that's not always possible. One of the benefits of using reflashing software is that you can change settings whenever you like, as often as you like. So if you plan to make additional modifications, (such as the ported heads/cam installation we have planned for our Silverado) you can re-optimize settings as required. Some tuners also offer free or low cost "re-do's," so even if you don't have reprogramming software, you can have your truck's computer updated very economically.

The same techniques that we used on our 5.3-liter small-block can be applied to virtually any other engine. Diesels require a slightly different approach, but they are just as easy to modify. We'll cover the specifics of diesels and other gas engines in future editions of "Tow Story."

SOURCE
EFI Live
New Zealand
SPAL USA
8-00/-345-0327
www.spalusa.com
Random Technology
7-70/-554-4242
randomtechnology.com
  • «
  • |
  • 1
  • |
  • 2
  • |
  • 3
  • |
  • View Full Article