Hennessey Camaro HPE650 vs SpeedFactory Challenger SRT8 vs Shelby GT500 Super Snake

[RACER X]

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Texas-size braggadocio started this retro-car rumble. Back in January, famed Houston-area tuner John Hennessey released plans for a 705-horsepower, ZR1-engined 2010 Camaro. Naturally, this sent forum boards buzzing about when and how Ford would respond with its 2010 Mustang.

Not two weeks later, a white-hot press release out of Las Vegas landed in our inbox, detailing Shelby's plan for a 725-horsepower Mustang GT500 Super Snake. And just like that, the ultimate musclecar battle had begun. The easy match-up would have been simply to let these two braggarts throw down in an asphalt octagon, but we wanted more. So we set about arranging a 700-horsepower trifecta and went looking for a Challenger with enough swagger to go tire to tire to tire with Shelby and Hennessey.

Like those two, our Dodge tuner would have to deliver a complete turnkey vehicle, not just a crazy custom build. We looked for OEM levels of fit, finish, and reliability, backed by warranties and customer service.

With his Camaro already in the mix, Hennessey was out as the Challenger tuner. We took a careful look at legendary musclecar builders Mr. Norm and Hurst Shifters as both had created some serious SRT8s for last year's SEMA show. Problem was, Mr. Norm's 900-horsepower Super Challenger is an overpowered one-off, while his regular Super Challengers don't make enough ponies. Neither do the Hurst Challengers; the top-step Hurst Series 5 SRT8 promises but 572 horsepower.

Enter SpeedFactory of Morrow, Georgia. Though lacking the celebrated status of Mr. Norm or Hurst and the street cred of Hennessey, SpeedFactory is a serious player in the realm of Dodge performance. As the first to offer turnkey upgrades for the modern Mopar musclecars, SpeedFactory serves up Challenger SRT8 modifications from a Stage 1 cold-air-intake upgrade that adds 25 horsepower all the way up to a stroked and supercharged Stage 6 vehicle that delivers 1000 horsepower and 10-second quarter miles. SpeedFactory's 700-horsepower Stage 5 setup seemed just the ticket.

With the triumvirate locked down, we set a date and some ground rules to keep things honest. To ensure nobody felt compelled to send a slicked-out, race-gas ringer, we stipulated 91-octane fuel and high-performance street tires only. We also told our tuners the first order of business would take place at K&N Air Filters headquarters in Riverside, California. Why there? Because K&N has an immaculate set of automotive lie detectors known as Dynojet Research chassis dynamometers. During the preparation period, problems cropped up big and small. A month before our showdown, Shelby Automobiles sent out a follow-up press release revising the Super Snake's output to 750 horsepower. This didn't bother us or the other tuners too much; at these astronomical output levels, a 45-50-horsepower difference represents only a seven-percent advantage.

But then, two weeks later, Hennessey called to inform us that his HPE700 wouldn't be ready in time. The ZR1's LS9 V-8 couldn't fully communicate with the Camaro's CAN-bus electronics and would take too long to sort out. In its place, Hennessey promised to deliver a 650-horsepower HPE650 Camaro, which adds a Magnuson TVS2300 supercharger, high-flow fuel injectors, custom ECU tuning, and a stainless-steel exhaust to the Camaro's LS3 V-8. Hennessey knew this might put him at significant disadvantage to the other full motor swappers, but since he was okay with it, so were we.

Two days before our scheduled throwdown, SpeedFactory dropped the biggest bomb. Its Stage 5 Challenger wouldn't be making it. After completing the Stage 5 392-cubic-inch crate motor swap, supercharger installation, and full dyno tune weeks in advance, the guys pulled the ultimate rookie move -- they got greedy. Apparently somebody at Mopar Performance dangled the promise of an all-aluminum, bored-and-stroked 7.2-liter Hemi, and the guys jumped at the chance to incorporate this engine and take 200-300 pounds out of the big Dodge's nose. However, an all-new engine meant all-new problems. Delays pushed the build to the 11th hour, and once they finally did get the engine and hop-up parts fitted, faulty communication between the ECU and crank-angle sensor scuttled the whole project. Or did it?

After a few courteous phone calls and politely worded e-mails, we managed to convince the SpeedFactory guys that getting their Challenger to our little shindig -- whatever its condition -- was in their best interest. Then we took a deep breath. With our 700-club plan effectively trashed, we headed to K&N curious to learn how this would all play out.

On its third pull, the blackish-blue Super Snake lit up K&N's dyno to tune of 635 horsepower and 581 pound-feet of torque at the rear wheels. Pretty impressive for what was essentially a GT500 with an upgraded Whipple supercharger, twin billet 75mm throttle bodies, and a revamped Borla exhaust. Factoring in drivetrain losses of 15-20 percent, the Super Snake was delivering on its promise of 750 horsepower at the crank.

Next up was the HPE650, which should have put down roughly 550 wheel horsepower if Hennessey's claim of 650 crank horsepower were true. When it put down 612 horsepower and 593 pound-feet of torque, our eyebrows and spirits rose. Perhaps the Super Snake wouldn't just slither away with all the accolades.

Or maybe not. SpeedFactory puts its Stage 5 Challenger SRT8 at 700-plus horsepower to the wheels, yet it managed only a paltry 454 horsepower and 429 pound-feet of torque on the dyno. This despite a Vortech blower, water-to-air intercooler, and stainless-steel Corsa exhaust with high-flow catalytic convertors. What gives? A nearly unfathomable error as we'd find out later.

After the enlightening session at K&N, everyone was eager to see how the dyno champ would do at the test track. Spinning rollers in fourth gear is one thing, but would there be enough grip from the Shelby's 285/30R20 Pirelli PZeros to contain 635 horses on untreated asphalt?

Road test editor Scott Mortara tried every trick in his book to execute a clean launch in the Snake but to no avail. "Getting a good, hard launch is next to impossible. It's all about trying to not let the tires spin too much, because, no matter what, they are going to spin," said Mortara. The best he could do was 4.1 seconds to 60 mph-no better than a regular, 540-horse GT500. The quarter mile came in 12 seconds flat at 120.1 mph compared with 12.4 seconds at 116.0 mph for its little brother. Could the Hennessey do any better with less horsepower and more torque, wider tires, and, most important, an independent rear suspension?

THE DYNO DOESN'T LIE

The Super Snake's impressive fury on the dyno comes from a 5.4-liter V-8 and Whipple, Roots-type supercharger codeveloped with Ford Racing. It's hard to believe the smallest engine here puts out by far the most power. What's even harder to believe is that the smallest, lightest, most powerful car here is not the fastest.

More impressive than the 722 crankshaft horsepower (using an 18-percent loss due to drivetrain inefficiencies) is the torque curve, which is taller and wider than the Super Snake's. At 2000 rpm, the HPE650 makes 475 pound-feet of torque. Peak occurs at a useable 3960 rpm-outstanding for an engine using stock internals and a mild 8 psi of boost.

Why so low? SpeedFactory's Stage 5 SRT8 was supposed to come with a brand-new all-aluminum Hemi, bored and stroked to 7.2 liters. Instead we got a standard-issue 6.1 SRT8 Hemi with upgraded fuel injectors, a Vortech V3 centrifugal supercharger, air-to-water charge cooler, and Corsa exhaust.

Snake on dyno: K&N has been making air filters for over 35 years. As part of its research and development operations, K&N tests the fit and performance of all its products in an impressive facility at its headquarters in Riverside, California. For automotive applications, the company has an immaculate dynamometer room, featuring a two-wheel and all-wheel-drive in-ground Dynojet. K&N also has an all-wheel-drive Superflow duno with linked rollers that move at exactly the same speeds. This allows for testing of newer, high-performance cars with complicated traction control systems. Beyond the impressive hardware, K&N's staff is knowledgeable, friendly, and composed of enthusiasts just like us.