Late Model Hemi Engine Upgrades - Hemi Hop-Up

We were back at SLP so we... 

   

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We were back at SLP so we could further flog their latest go-fast goodies available for the late-model Hemi (Charger, 300C, and Magnum). Ed Hamberger's SLP crew used their Charger Daytona mule and a willing friend's (Eddie Perez) SRT8 to design, test, and manufacture their latest performance products.

Once again we were back to resume testing of more of SLP's recently developed products for the new Hemi. Rewinding to the April 2007 issue article "Happenin' Hemi Headers," SLP's headers and exhaust yielded an additional 21 rwhp and 31 lb/ft of torque of the factory system. The important average gains from 3,000 to 5,000 rpm were 33 rwhp and 30 lb/ft of torque. At the track, this equated to a drastic half-second reduction in e.t. This really caught our attention--these late-great Hemis really respond to the old-school upgrades.

After that test of the headers and exhaust, SLP developed a Cold-Air Induction Package, Power Programmer, and an Underdrive Balancer/Pulley. The first product they designed, tested, and manufactured for production was the Cold-Air Induction Package. It replaces the stock restrictive air box assembly. This high-airflow, power-enhancing system proved to be worth 7 rwhp on the SuperFlow chassis dyno. That amount of power improvement is worth an easy tenth at the track.

Next, SLP and DiabloSport spent time collaborating to co-develop the handheld tuner/power programmer. All of their R&D work paid off and enabled the power programmer to be worth 12 rwhp and 11 lb/ft of torque. The SLP/DiabloSport programmer has performance tunes specific for their 5.7 and 6.1 Hemi PerformancePacs. These handheld devices can perform multiple custom tunes, transmission shift points/firmness, vehicle speed and engine rev limits, cooling fan speed/temperature adjustments, along with all the many DiabloSport tuner features. Most owners of bone stock, late-model Hemis want to remove the conservative (and usually pig-rich) factory tuning for a more aggressive tune suitable to their high-performance taste.

Another effective bolt-on for gaining power is an underdrive crankshaft pulley. The Third-Gen Hemi utilizes a one-piece balancer/pulley assembly, and SLP recently began offering a high quality, SFI approved unit that adds 9 hp and 10 lb/ft of torque to the rear tires. Having road- and strip-tested SLP's Daytona before and after the balancer/pulley swap, the Hemi feels as smooth, if not smoother, than ever. In addition to a performance gain due to less rotational drag, an underdrive pulley means better fuel economy and longer accessory (alternator, a/c compressor, p/s and water pump, tensioner pulley) life.

Adding the total power gains of 28 rwhp from the three new power producers made us anxious to get back to our favorite test track, Raceway Park, E-Town (Englishtown, NJ). The day before our track date, SLP's Hank Danieki, chief engineer, asked if we could possibly test customer Eddie Perez's SRT8 Charger. We said sure as long as it was the car we spied them installing their headers, exhaust, and cold-air induction on. Hank assured us it was indeed that car.

While driving SLP's Daytona mule-car to the strip (a one-hour ride) we tried different tunes and automatic shift points and firmness. Man, what these handheld tuners can do in minutes would take many knuckle-busting hours to do on our old Mopars. At the track, we achieved our lowest e.t.'s using the tuner's best performance tune along with 6,000-rpm shift points. For the 6.1 Hemi, we found 6,400-rpm upshifts to be ideal.

Both Hemi cars have their differences when trying to launch out of the hole. The Daytona can be punched off-the-line, but for big brother SRT8, it's not an easy task on stock tires. Eddie, who had drag raced his Charger the previous weekend, was having traction issues. The best hook and 60-ft e.t. came by precisely-timed go-pedal depression. It had to be slightly slower than when stomping the pedal of the Daytona. On the scales, the SRT8 weighed nearly 200 pounds heavier than the Daytona (4,440 vs. 4,250 pounds). The 6.1 has a cast-iron block while the 5.7 is aluminum alloy. Beefier sway bars, wheel, and tires also explain the added poundage of the SRT8.

This Cold-Air Package (PN...        read full caption This Cold-Air Package (PN D21002) is available for the 2005-and-up 5.7 Hemi cars. For the 6.1 Hemi, the easy-to-install kit for Cold-Air Induction is PN D21003.	Here is Hank Denieki, SLP's...        read full caption Here is Hank Denieki, SLP's chief engineer, using the handheld tuner to raise the shift points on Eddie's SRT8 before we made any passes down the quarter-mile. Our best e.t. came from firmer-up shifts at 6,400 rpm for the 6.1 and 6,000 rpm for the 5.7 Daytona. The handheld tuners are tailored to SLP's performance parts upgrades and their PerformancePacs.	Here's the before-and-after...        read full caption Here's the before-and-after look going from the ugly, restrictive factory air cleaner assembly to SLP's high-flow induction on their Daytona.
The cold-air induction showed...        read full caption The cold-air induction showed a gain of 7 hp and 6 lb/ft of torque at the wheels.	The 25-percent underdriven...        read full caption The 25-percent underdriven Balancer/Pulley adds 9 hp and 10 lb/ft of torque to the rear tires. It's lighter than the stock balancer and is 100-percent steel construction and SFI approved. Also featured are taller retention walls that reduce the chance of belt slippage and thrown belts.	Both cars were equipped with...        read full caption Both cars were equipped with the Brake-Control Package (PN D25000) from SLP. This well engineered kit is fully compatible with the factory anti-lock and traction control systems. The kit has everything needed to just bolt and wire it in. There's no cutting, flaring, or fabricating necessary, and the kit comes with easy instructions.
Once installed, press the...        read full caption Once installed, press the brake pedal, flip the toggle switch (shown mounted ahead of the shifter) to activate the electric solenoid (mounted underhood), then remove your foot from the brake pedal and smoke em' up. The Brake-Control Package (AKA line-lock, roll-control) will minimize beating up on the rear brake components.	These mandrel-bent 409 stainless,...        read full caption These mandrel-bent 409 stainless, ceramic-coated headers (1¾-inch primaries, 3-inch collectors) are manufactured at SLP's facility in New Jersey. They were developed for the 6.1 SRT8 LX cars after we tested the 5.7 headers and exhaust. The 3-inch high-flow bullet catalytic converters go into 3-inch down pipes. They'll bolt up to the factory exhaust or any of SLP's three available exhaust systems (Loudmouth, Loudmouth II, or PowerFlo).	The SLP headers feature a...        read full caption The SLP headers feature a great fit, factory ground clearance, and power gains of over 16 rwhp and 17 lb/ft of torque compared to stock manifolds. Those gains were realized while still using the stock restrictive exhaust system. The header kit features an OEM-quality O2 sensor extension harnesses. After the headers, the exhaust is made from 304 stainless, and everything carries a lifetime warrantee.