2008 Hennessey Jeep Grand Cherokee SRT530 Road Test

Startling Sound, True Speed and Not Trail-Rated

Published: 05/19/2008  - by Scott Oldham, Editor in Chief

The guy in the Prius is actually afraid. It's in his eyes. Fear. Pure fear. No, wait, that's not fear. It's disgust. Pure disgust.

Perfect.

We're driving Hennessey Performance Engineering's SRT530 version of the Jeep Grand Cherokee SRT8. Compared to the company's ludicrous 1,000-horsepower, twin-turbocharged version of the Ford GT we drove in April, this 530-horsepower Jeep is like getting a back rub, but to the optimist in the glorified golf cart it's the end of the freakin' world.

Must be the satanic rumble coming from our truck's two Howitzer-size exhaust pipes. This puppy isn't stock, and Al Gore in the next lane ain't happy about it. Apparently, an all-wheel-drive SUV with a 500-plus-horsepower 6.1-liter V8 and 20-inch wheels and tires doesn't fit into our friend's version of the world. It's too loud. Too fast. Too thirsty. Oh, and too much fun.

Don't worry, buddy. The light will turn green any second now and it will all be over. We'll leave you and your NPR podcast in the dust.

Classic Hot-Rodding
This truck's creator, John Hennessey, has spent his career pissing off the Greenies. He swells Viper V10s so big they swallow up the atmosphere in country-size gulps. Then, when that isn't enough, he adds turbochargers, with turbines so enormous they ought to be hanging under the wings of 747s. He's king of the Silver State Classic and lord high chancellor of the Texas Mile. No matter how stupidly fast a car is from its original factory, Hennessey is sure he can make it faster. He even has an active tuning program for the Bugatti Veyron.

With its 420-hp 6.1-liter Hemi engine, the Grand Cherokee SRT8 already qualifies as the most ridiculously overpowered production Jeep ever. It's also clearly the quickest, slashing to 60 mph in just 5.2 seconds and thumping through the quarter-mile in 13.49 seconds at 102.24 mph. For a vehicle that weighs in at 4,788 pounds and has the aerodynamics of an adobe hacienda, that's blazing.

Still, Hennessey knew the Jeep could go faster. Much faster.

Get Wrenching
To find speed, Hennessey ports the cylinder heads and punches the Hemi's compression ratio up from 10.3:1 to 10.6:1. On the intake side a cold-air induction system keeps it fed with chilly oxygen. Meanwhile, exhaust is handled by stainless-steel long-tube headers, stainless-steel midpipes feeding high-flow catalytic converters and, finally, 3-inch stainless-steel pipes capped by 4-inch polished tips.

More suck. More squish. More bang. And more blow. It's a formula that has made horsepower for more than 100 years. But today you've got to bust out the laptop to make it all work, so Hennessey also cracks open the Jeep's engine management computer and reprograms it.

All those tweaks, twangs and tickles are enough, says Hennessey, to knock engine output at the crank up to 530 hp at 6,000 rpm and 530 pound-feet of peak torque at 4,200 rpm. That torque claim is particularly impressive, since the stock SRT8 produces its 420 lb-ft peak while the engine is spinning 600 rpm faster.

Well Enough Alone
What Hennessey doesn't touch is the Jeep's five-speed automatic transmission or its all-wheel-drive differential. And the test vehicle wears the stock brakes and stock 20-inch wheels and P255/45ZR20 front and P285/40ZR20 rear Goodyear Eagle RS-A tires.

Throw in such aggrandizing plucks as exterior badges and floor mats with the "SRT530" logo, a "limited edition" dash plaque, a "limited edition" engine plaque and a pair of "Powered by Hennessey" red valve covers, and that's what constitutes the SRT530.

For all this, Hennessey charges $15,900, including installation and a road test of at least 100 miles. That's a lot for a 110-hp hype up in power, but modest by the standards of what Hennessey charges on other vehicles. Of course you have to supply your own Grand Cherokee SRT8.

Classic Thrust
Still, it looks like a stock Grand Cherokee SRT8. For many buyers that stealth factor is peachy keen. Ours would wear some aftermarket wheels for distinction and some grippier rubber.

That said, this brick is a rocket. Getting from a dead stop to 60 mph takes only 4.6 seconds (4.3 seconds with 1 foot of rollout like on a drag strip) and the quarter-mile vanishes in 12.9 seconds at 106.7 mph. Even though it weighs 4,722 pounds, it launches as if shot from a gun: a 16-inch gun on the deck of an Iowa-class battleship.

It doesn't take much technique to get that performance, either. It's really a matter of turning off the traction control and then letting the all-wheel-drive system do the rest as the transmission upshifts with brutal efficiency. Is a 6/10ths improvement in 0-60 performance and almost 6/10ths off the quarter-mile time worth $15,900? That's a question that's strictly between you and your Visa card.

The power itself is exceptionally friendly with the throttle still being sweetly progressive, and there's never a hiccup in how it's delivered. Aside from the thrust, the most evident change with the SRT530 is the incredible sound. This thing isn't slightly louder or has a slightly modified exhaust note: It sounds like what NASCAR stock cars want to sound like when they grow up. Before you buy, be sure your employer's benefits package includes hearing care.

Classic SUV
Otherwise Hennessey's SRT530 drives very much like a regular SRT8. Under braking it still nose-dives like Greg Louganis (60-0 in a so-so 124 feet); on the skid pad the tires yelp and wail like the audience at a Miley Cyrus concert, and the understeering adhesion is modest (0.84g); and the slalom run is good for its size and weight (63.6 mph). None of this should be surprising considering that Hennessey didn't touch the chassis, and there's nothing exotic about double wishbones up front and a solid axle on coil springs in back.

Equally not surprising is this tank's fuel economy. In stock form, the Grand Cherokee SRT8 is rated by the EPA at a miserable 11 mpg in the city and totally cruddy 14 mpg on the highway. We wouldn't be shocked if normal commuting would have this monster delivering single-digit fuel economy.

For those hard-core fanatics out there willing to pay any price for performance, Hennessey also offers a turbocharger system for the Grand Cherokee SRT8 that thumps out a claimed 620 hp and turns the vehicle into an SRT600.

After all, if you're going to spit in the eye of society you may as well shoot a big honking loogie.

Don't worry, Mr. Prius. Phlegm is biodegradable.

Hennessey Performance Engineering provided Edmunds this vehicle for the purposes of evaluation.