If you're like most Corvette owners, you enjoy the driving experience that's only available when you're behind the wheel of America's sports car. But if your Corvette is a race car, show car, project in process, or simply in need of repairs, the occasion may arise when towing it makes a lot more sense than driving it. If that's the case, having a tow vehicle with ample power is essential to safer and easier towing.
Although the engines in most late model 1/2-ton pickups-particularly those wearing Chevrolet and GMC badges-have horsepower ratings that were unheard of a few years ago, they may still struggle a bit when a loaded trailer is hooked to the rear bumper. The techniques used to improve the performance of different engines are similar, so even though our test truck is a Chevrolet Silverado, results are typical of what you can expect from other makes.
Chevrolet's Silverado and GMC's Sierra, which share the same powertrain, have been equipped with 4.8-, 5.3-, and 6.0-liter LS-series engines since the 1999 model year. Rated at 285-315 horsepower depending on model year, the 5.3 is the engine most commonly found in pickups that are used for light towing. Even if you don't have a truck, or have no interest in modifying one, you might find the following of interest because the 5.3 truck engine is essentially a cast iron, small bore version of the 5.7-liter LS1 Corvette engine.
As is the case with your favorite Corvette engine, improved air flow and reduction of parasitic power losses are two important keys to improved performance. The relatively simple modifications we made to our '02 Silverado test vehicle resulted in horsepower and torque readings of 268 and 308, (at the wheels) increases of 24 horsepower and 15 lbs./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've also developed a towing-oriented heads/cam package for the 5.3. Let us know if you'd like more information on it.)
The horsepower increase we recorded is a bit irrelevant, but it does put some of the advertised claims you may see into perspective. In a tow vehicle, peak horsepower isn't of much concern or value because chances are pretty slim that you'll have the gas pedal on the floor, and the engine spinning at 5500 rpm, when there's a trailer hooked to the rear; mid-range torque is of far more practical importance. The same holds true for Corvette engines. Even though you may bounce your engine off the rev limiter occasionally, it spends most of its time at the lower and middle ranges of its rpm band. So although big power numbers are great for bragging rights, trading off some top end power for increased mid-range torque usually makes a car more fun to drive and easier to tune.
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; '07 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 we removed the mechanical fan is further evidence of its negative impact on power-and fuel economy. Our '02 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.