Stealth S-15

The Air Force has a black stealth fighter called the F-117 that has proved to be as sneaky as it is deadly in battle. Tuner impresario John Lingenfelter has his own four-wheel version—painted a more pleasing red. Both will sneak up on you and hit you hard, even when you are paying attention.

Lingenfelter has this thing about looking stock and carrying a big stick. Last year he bought an ’01 four-wheel-drive S-15 Sonoma pickup and it remained stock for about 30 seconds after it arrived at Lingenfelter Performance Engineering (LPE). At the same time, Lingenfelter was neck-deep in the Pro Stock Truck wars with his Summit-sponsored S-15 Sonoma pickup. For mere mortals, racing and running a business would be challenging enough. But when the after-dinner napkin plan materialized, Lingenfelter had no option but to build the stealth S-15.

In classic Lingenfelter fashion, the plan was aggressively simple. LPE has been building twin-turbocharged LS1-powered Corvettes for several years, and the power these cars make is nothing short of awesome. The biggest problem is traction. So Lingenfelter decided to blend the Vette twin-turbo technology with a 427ci LS1-based small-block and all-wheel drive into a pickup to run in the 9s. The concept revolves around a 4L60-E overdrive automatic and transfer case out of a GMC Yukon spinning the front differential by way of a factory GM viscous coupling.

In order to fit all this north-south madness into a stock S-15 floorpan, Lingenfelter’s fabricators Mike McLain and Scott Walters began the arduous task of slicing the trans tunnel and raising it one inch to allow the LS1-based small-block to clear the front axle. Once that happened, they managed to stuff the small-block into the engine compartment along with the twin Garrett >> turbochargers—all with a Detroit visage.

The gritty details have more to do with plumbing the intercooler than mining for power. Initially, Lingenfelter packaged both an air-to-air intercooler and the engine radiator in the usual place behind the grille. While this worked well, the small intercooler created a disappointing pressure loss when attempting to spin up double-digit boost numbers. Once Lingenfelter decided to think outside the box, this led to transplanting the radiator into the bed of the truck.

With the radiator migration complete, Lingenfelter’s fabricators installed a large-by-huge air-to-air intercooler in the area vacated by the engine radiator. Subsequent testing revealed 250-degree F discharge temperatures out of the turbochargers that dropped to roughly 5 to 10 degrees above ambient air temperature exiting the intercooler with less than a ½-pound of pressure loss. Subject any engine to 10 psi of boost with an 80-degree inlet air temperature and you have a recipe for riotous power.

Of course, massive torque often uncovers the weak link in the drivetrain. In this case, it’s the 4L60-E transmission. Lingenfelter’s drag testing has revealed that the excellent four-wheel traction means the truck is capable of a 1.4-g peak while maintaining 1 g acceleration up to 40 mph. This pushes the oil in the transmission to the rear of the sump, which has caused shifting problems and burned clutches. Lingenfelter already has a fix in mind and that, along with more boost, means 9s are not far off.

Lingenfelter aimed all of this effort at creating a fully streetable pickup that looks like every other little S-series pickup in the world yet was brutally quick. This meant that it had to be functional too. On test day, we drove the truck to the dragstrip in Muncie—about a 45-minute drive away. The A/C can frost-up the interior while it cruises like any other 21st century stocker. But stab the throttle and the truck really hustles. The trick was to have the front wheels pointed straight when the boost came in because when that happened, the truck instantly leaped toward wherever the front tires were pointed.

Once at the dragstrip, the Sonoma continued its stealthiness because the launch was so deceiving. But once the boost came on, it absolutely marched down track. After a series of consistent 10.60s at 131 mph, Lingenfelter managed to generate a little boost on the starting line, pulling off a 1.58 60-foot time on its way to an impressive 10.48/132.15-mph pass.

Lingenfelter says once he improves transmission life expectancy, he can then pump the boost up and this red rocket will hustle right into the high 9s on radial tires and pump gas. If that’s not enough, on a recent drive across the state, the little truck knocked down 18 miles per gallon. If it gets any better than that, you call us.