It seems like every Mopar maniac wants a new Challenger, and even Brand-X guys appreciate the styling. In fact, we've spoken to regular (any brand) folks who mentioned they like the Challenger's styling over the new Camaro. Many owners of these new dream machines modify them just like owners did back in the day. The aftermarket has jumped into this new market with their feet first-and that's a good thing! The first modification most people do to their new Hemi is to let them breathe and be heard. For this test, we checked out SLP's variety of exhaust system possibilities in decibels, power, and elapsed times.

This all started with a bi-annual visit to the folks at SLP Performance. At this point they had designed, installed, and tested their headers and exhaust on quite a few Challengers. We had already put SLP's goodies to the test on the Chargers we flogged in the May '09 issue of Mopar Muscle ("Hemi Hop-Up"), and were anxious to see what kind of results we'd see on the Challenger. Luckily we had a friend with an unmolested '08 Challenger SRT8. Sam Mandarine offered us his low-mileage Challenger SRT8 (1,600 miles before testing) to use. We thank him for letting us use it as a guinea pig for the install of the SLP 475 HP PerformancePac (Headers, exhaust, air intake, underdrive balancer/pulley and power programmer) as well as the before and after strip and dyno tests at SLP.

The 90-minute ride to Englishtown for baseline runs and the ride home was time well spent. The thrill drive to E-town helped us find optimum shift points. We noticed the automatic 1-2 shift point came in too early at 5,400 rpm, while the 2-3 shift point felt perfect at 6,200. After a one-hour cool-down, we made a pass while manually shifting at 6,200 rpm. We were stoked to see the scoreboard show a sizzling 12.90 at 108.27 mph. E-Town's starting line was well-prepped and we were blessed with good autumn air. We made a backup pass and slowed to a 12.97 at 108.07 mph. This was unlike the Hemi Chargers we tested in the May '09 issue, which ran quicker on the backup run. Another one hour cool-down and the 6.1 produced a 12.91 and a 12.97 backup pass.

This time around we would add a twist and sound-test the three different exhaust systems (Loudmouth, Loudmouth II, and PowerFlo) that SLP offers. If you choose to mix and match the mufflers, there's the possibility of six different levels of sound for anyone's personal preference. We used a sound decibel meter to test four exhaust configurations and different levels of noise. Interior decibels readings were observed at idle and at a full throttle 50 to 70 mph blast. Exterior audio was checked at 30 feet and 3,000 rpm. Decibel readings "going down the track" were only taken while strip-testing with the stock and PowerFlo exhaust system (final exhaust configuration).

Sam's choice of exhaust was the PowerFlo so his wife could clearly hear music from the Challenger's sound system. The underdrive balancer/pulley, high-flow air intake, and the power programmer were installed to complete SLP's 475 HP PerformancePac. Then the late-model Hemi car headed over to SLP's in-house dyno. There it made an SAE corrected 480 horsepower at the crankshaft, proving itself as a better than average strong runner. See the dyno charts for the gains.

Our track date was hindered with unfavorable weather conditions (higher humidity and a lower barometer than the baseline) not allowing the bolt-on components to show their full power punch. After our usual one hour cool-down, we ran a 12.59 at 112.29 mph. Despite the bad air, we picked up a full 4 mph in trap speed. That's impressive, considering the test weight of 4,200 pounds. With good air, similar to the baseline, 12.40s would have been possible. Nonetheless, SLP's simple upgrades once again prove to be a real performance package. Follow along for the complete results from the exhaustive sound, dyno, and strip testing.