By the third run down the test track, I was getting a little too giggly. Perhaps it was from the Viper RT/10-like acceleration of the nitrous oxide-boosted Hennessey Prowler GTX. Or maybe it was the whiff of the laughing gas I got when the system was purged prior to testing. Either way, I was having loads of fun, which is the sole reason for owning John Hennessey's latest creation.
"The whole essence of a hot rod is to go fast and look good," says Hennessey. With the GTX, Hennessey improved the Plymouth Prowler's already audacious appearance a little bit and made it a whole bunch faster.
From its introduction, the Prowler's emphasis was on "show," with "go" an afterthought. Even after a '98 upgrade to a 3.5-liter/253-horsepower SOHC V-6, the stock Prowler looked a lot faster than it went. Hennessey's challenge was to make the Prowler significantly faster for a reasonable price. Rather than supercharging the existing engine or transplanting in a V-8, Hennessey chose to add a nitrous oxide injection system. Other engine work was limited to light head porting, a freer flowing exhaust system, and a low-restriction K&N air filter. These last modifications up the GTX's horsepower to 290. But flip the nitrous switch (located in the console between the seats), go to wide-open throttle, and the GTX can reach a peak of 365 horses and a whopping 450 pound-feet of torque. The result is 0-60 mph in blazing 4.5 seconds with a rapid 13.1-second/105.3-mph quarter mile. Compare that not only to a stock '99 Prowler (0-60 mph in 5.7 seconds, with a 14.3-second/95.4-mph quarter), but more significantly to what we got a few years back from a '93 Dodge Viper RT/10: 4.5 0-60, 13.2 at 112.1 mph in the quarter. In anybody's book, the Hennessey Prowler GTX has plenty of "go fast" to accompany its "look good
With the GTX, Hennessey focused totally on the straight-line acceleration, so much that, in deference to Hennessey's customer's tires, we didn't even run it through our handling tests. The handling numbers in the accompanying chart are from a stock '99 Prowler.
Without the laughing gas, it's hard tell the GTX from a stock Prowler. It feels marginally more muscular and, thanks to the headers and air filter, slightly louder. Even when armed, the nitrous system is transparent. The bottle heater automatically switches off when the nitrous reaches the proper pressure, and no juice goes to the engine until the throttle is flat to the floor. Drive sedately, and you can leave the system armed all day. Even a partial lift off the accelerator pedal immediately shuts off the gas.
Hennessey employed a Nitrous Express controller that permits virtually infinite adjustment of the amount and timing of the nitrous delivery. For our testing, the system delivered 100 percent of its capacity as soon as wide-open throttle was reached. This required me to roll off the line at part throttle to prevent speed-robbing wheelspin. But to avoid spinning the huge 295/40ZR20 tires during street driving, you could choose to progressively ramp up nitrous delivery.
(If you thought "dental surgery" at the first mention of nitrous oxide, here's a quick primer: Nitrous helps an engine produce more power primarily by carrying more oxygen to the combustion chamber, which allows the engine to burn more fuel. Also, when compressed nitrous oxide expands, it cools the intake charge, which increases output potency.)
The twin, trunk-mounted 5-pound nitrous bottles-connected to the manifold by steel-braided hoses-are good for about a half-dozen full passes down the dragstrip or an evening's worth of stoplight-to-stoplight sprints before they run dry.
In the "looks" department, Hennessey removed the bumpers, a move he says is legal, at least in Texas. The rear mounting points were covered with a roll pan. Up front, the turn signals were moved from the bumper to the grille and small panels were fabricated to cover the bumper mounting points. No suspension work was performed. The stock Goodyear Eagle GS-Ds on stock wheels also were retained. Stickier, wider rear tires might have chopped another tenth or two off the 0-60-mph time.

Total cost for the entire package is about $15,500 installed at Hennessey's Houston, Texas, shops.

Our verdict: The Hennessey GTX package is a relatively easy, relatively affordable way to give the Prowler some serious go-fast. And, yes, I'm still grinning.

Hennessey Prowler GTX  Specifications

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