The 1990s were an important time for V-10 engines, marking a resurgence of a configuration that had once been the sole providence of supercars and foreign exotics. Ford's Modular engine, introduced in 1991, has lived up to its name in spades by expanding from a milquetoast 281 cubic inch V8 all the way to the thumping 413 cubic inch Triton V-10. While undoubtedly powerful and versatile, the Triton isn't exactly the fuel economy champ of its family, especially when pared with the massive F-250 chassis. Still, boosting your truck's road-thriftiness need not necessarily mean killing its fun factor.
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Install a rear-mount twin-turbo system by purchasing the universal components and fabricating the rest yourself. Yes, adding a turbo to increase fuel mileage may seem a little backward, but you'll see the logic in a moment. Obviously, fabricating a twin-turbo system is beyond the scope of a 700-word article, so if you don't have sufficient fabrication skills then enlist the services of someone who does. Start with a low-boost turbo system engineered for a 4.6-litre modular Mustang and make it fit by installing longer turbo-to-engine plumbing.
Install numerically-lower rear axle gearing, in the range of about 2.2 to 2.25-to-1. This axle gearing is the key to keeping your newly-turbocharged engine in its key efficiency range. The lower gearing will keep rpm down while allowing you to modulate the engine's required power output by adjusting turbo boost. In this way, the turbos act as sort of a variable-displacement mechanism, pumping only as much air into the engine as it needs to maintain a given speed with a given load.
Install a set of shorter, skinnier tires on the front and rear. The F-250 comes stock with 16 by 7 inch rims and LT235/85R E-rated tires; go for a set of LT180/70 tires for a 2.5-inch drop in ride height. Select a set of tires with a very hard, long-wearing rubber compound for reduced rolling resistance and increased mpg. If you have dual rear tires, dump then and use a set of singles. The shorter tires will numerically increase the effective final drive ratio by about 17 per cent, which is part of the reason for the higher gearing from Step 2.
Strip as much weight as possible from the truck. At 2540 Kilogram, your truck is never going to be a Lotus, but every pound you can take off will decrease the amount of boost you'll need to maintain the performance you're after. You could rip the 4WD axle, transfer case and running gear out to save a few pounds and reduce rolling resistance, but you'll regret it with skinny tires and 500-plus horsepower of turbocharged Triton on tap.
Enhance your truck's aerodynamics by installing a set of performance lowering springs, stiffer shocks, a Tonneau cover and a full sheet-metal "belly pan" to cover the bottom of your vehicle's chassis. An air dam installed under the front bumper will keep drag and lift-inducing air out from under the truck, but you'll need to install a vented hood and fenders to evacuate engine heat. The end result will be greater fuel efficiency and stability at highway speeds. The F-250 comes with 8.3 inches of ground clearance stock, so even after installing the 2.5-inch shorter tires you can still lower it by about two inches while maintaining a reasonable four inches of ground clearance.
Tips and warnings
- Follow this recipe and your engine will end up practically idling -- 1,300rpm or so -- at 60mph. Keep the 31-inch tall tires and drop the suspension by another 2.5 inches to compensate and you'll end up crawling along at around 1,050rpm. Without the turbos, your engine wouldn't have near enough torque to maintain 60mph. That's where boost adjustment will pay off, since you'll never have to burn more fuel than you need to in order to maintain speed.
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- "Race Car Engineering and Mechanics"; Paul Van Valkenburgh; 2001
- "Chassis Engineering"'; Herb Adams; 1992
- "New Directions in Race Car Aerodynamics: Designing for Speed"; Joseph Katz; 2003
- "Maximum Boost: Designing, Testing, and Installing Turbocharger Systems"; Corky Bell; 2003
- "Turbo: Real-World High-Performance Turbocharger Systems"; Jay K. Miller; 2008
- "Haynes Manual: Ford Super Duty F-250 and F-350, 1999 through 2002"; Haynes Publishers; 2003