While the 2010 Camaro and new 5.0 Mustang have gotten a lot of attention lately, the Mopar faithful are quick to point out that the reborn Chrysler HEMI powerplants were first-to-fight in the modern musclecar wars. These engines, by virtue of their head start in the market, have a ton of speed parts available, and we’ve installed our share of them on our project 2007 Dodge Magnum R/T. One link in the chain we haven’t yet upgraded is the factory exhaust system – though our wagon had a high-performance exhaust from the catalytic converters on back, it still wore its restrictive cast iron manifolds. To uncork that bottleneck, we went to SLP for a set of long-tube headers, high-flow cats, and midpipes.
Today’s experimental subject is PowerTV’s supercharged 2007 Dodge Magnum R/T
The HEMI is a terrific foundation for a performance buildup, and an aftermarket exhaust system is an easy way to enhance an already great engine. Factory exhausts are designed to be quiet, environmentally clean, and inexpensive to produce in huge quantities, which leaves a lot of room for improvement. Switching to tubular headers, high-flow cats, and less restrictive plumbing in place of the OEM mufflers and resonators is a sure road to better power.
The Vortech supercharger tucked under the hood put down a baseline of 375 rear wheel horsepower through the factory exhaust manifolds.
Our 2007 Dodge Magnum R/T with a 5.7 HEMI engine is in definite need of an exhaust upgrade. Our previous installation of a Vortech centrifugal supercharger really bumped up the power, but we suspect that we’ve reached (and blown right past) the limit of the stock exhaust system to keep up with the forced induction, and uncorking it should make a big improvement.
Since we needed an exhaust that could keep up with all the air being shoved in the front end, we chose a header package from SLP Performance Parts. They have a wide range of exhaust components for all late model musclecars. SLP Performance Parts now offers HEMI-powered Dodge Charger, Magnum and Chrysler 300C components to its lineup of late model parts they design, engineer and manufacture. We decided to go with a set of stainless steel long tube headers that also includes mating stainless steel pipes and high-flow cats, which can mount up to the OEM cat-back exhaust plumbing or an aftermarket system designed to mate to the factory converters, like the one we already have on our Magnum. SLP claims 15-plus horsepower improvements across the RPM range for this system on a naturally-aspirated car, and based on our dyno experience with long-tube systems, it’s not a stretch at all. In our situation, we were hoping for a lot more, since we suspected that our blower was being held back by the stock exhaust components.
The SLP Long-Tube header package for modern HEMI-powered vehicles includes everything necessary for installation, right down to gaskets and clamps.
We’ll take you through a complete overview of the long tube header kit from SLP, from installation to dyno testing. Previously, we dyno tested our Dodge Magnum before any exhaust components were added and the result was 374 horsepower and 391 ft/lbs of torque.
What’s in the Box
The SLP 2005-09 Long-Tube Header Kit comes with everything you need, which makes the installation process quick and painless. That means there’s no hunting around for gaskets, bolts, wiring, or any other bits and pieces to hold you up in the middle of the job. SLP’s long-tube stainless steel headers feature 1-3/4″ stainless steel primary tubes that merge into a 3″ four-into-one collector. The CNC laser-cut 3/8″-thick header flanges are designed to mate up perfectly with the stock HEMI heads.
The mandrel-bent headers are hand fabricated, then treated with an aluminum-ceramic coating inside and out, giving them a nice shiny finish. More importantly, this coating keeps heat confined within the headers, which helps maintain exhaust velocity and reduce underhood temperatures. Also included in the kit are two 3″ high-flow bullet-style cats that bolt on to the headers perfectly. The header collectors include bungs to mount the factory pre-cat O2 sensors. The stainless steel mid-pipes also have two locations for the rear factory O2 sensors. Because the long-tubes place the cats further back on the vehicle, SLP also includes four OEM-quality extension harnesses that plug directly into the existing harnesses and O2 sensors. To complete the kit, SLP includes header gaskets, header bolts, clamps for the catalytic converters and mid-pipes, and a bracket to relocate the factory oil dipstick. The SLP kit maintains factory ground clearance and good underbody-to header clearance and is completely compatible with factory EGR.
Installing the SLP Long Tube header kit on our Magnum follows the basic rules of any header installation. The job can be done entirely from under the vehicle, and with the proper tools it can be completed in 4-5 hours. Since SLP includes all the components needed, you won’t have to spend time hunting for extra parts.
Since the OEM O2 sensors will be reused, they’re removed from stock downpipes and manifolds first to keep them from getting banged up.
The first step was to disconnect the battery and get the car in to the air. We loaded the car on the 2 post lift and began removing the OEM exhaust components. We started wrenching by removing the OEM O2 sensors and placing the cables up out of the way. Next, we removed the cat-back and started unbolting the OEM downpipes and manifolds. We found that probably the most difficult part of this installation was actually the removal of the OEM heat shields that surround the cast iron manifolds. You’ll find that you need to bend them up a bit to squeeze them out between the frame and the manifold.
The stock downpipes with integrated catalytic converters and soup cans came out first…
…followed by the cast iron exhaust manifolds.
The manifolds will prove to be a little challenging to unbolt, but with the proper ratchet extensions, you can get at them without too many bad words. Since the header kit includes new bolts, there’s no reason to save the old ones. With everything removed from the car, we put the stock manifolds and the SLP headers side-by-side just to compare the differences.
With the SLP long-tubes and the stock “log” manifolds side-by-side, it’s obvious that the factory pieces were not designed with high flow as a primary consideration.
SLP provides quality Mr. Gasket brand gaskets in the kit – combined with the thick 3/8″ flanges, these assure a leak-free seal.
Starting with the driver’s side, we slid the headers up into place from beneath. Because of the long-tube design, bolting up the headers is actually easier than unbolting the stock manifolds.
The high-flow catalytic converters are secured to the 3” collectors with a stainless steel clamp. These cats won’t restrict the passage of spent gasses while they’re busy cleaning them up, and add an element of environmental responsibility to our upgrade.
The stainless steel mid-pipes clamp directly on to the cats and are necked down from 3″ to 2.75″ at the tail end to allow the cat-back to be connected to the mid-pipe.
The mid-pipes are bent to fit closely to the contours of the floorpan and provide the same ground clearance as the OEM exhaust.
The stock O2 sensors are reinstalled in the bungs in the collectors and mid-pipes, and plugged into the factory harness via the wiring extensions provided by SLP.
With the system in place, we made final adjustments to the position of the tubing, tightened all the clamps, then hit the dyno.
With the work of installation behind us, it was time to have some fun and see what kind of improvement we’d get on the rollers. You’ll recall that the baseline for our supercharged Magnum was just shy of 375 horsepower to the rear wheels with the restrictive stock manifolds and cats, so we were anxious to find out whether we’d be breaking the 400-horse barrier now that the exhaust was uncorked.
We rolled the Magnum onto the PowerTV dyno to quantify the fruits of our labor.
Though the SLP Long-Tube Header Kit is a true bolt-on, and under normal circumstances doesn’t require any retuning to see the advertised improvements in power, we made a few tweaks to the ECU to optimize our custom supercharger tune now that the HEMI could exhale as well as it inhales. If you’re interested in extracting every last pony and pound-foot from this swap, SLP offers a discount on their kit bundled along with a Diablosport Predator.
With the tune loaded and the Magnum on the rollers, it was time to make some pulls. Since the Dodge already had a performance exhaust, we didn’t expect much of a change in sound, but we were pleasantly surprised at how the long tubes and high-flow cats improved the sound when we wound the blown HEMI out.
After just two pulls on the dyno, we were rewarded with readings of 413 horsepower and 444 ft/lbs of torque, an increase of nearly 40 HP and 53 TQ. It’s clear that the stock manifolds were really holding our HEMI back, and while a naturally aspirated car won’t see these same huge gains, 15 horsepower now and the ability to support a bunch more later makes SLP’s Long-Tube Kit a slam-dunk even for NA late-model HEMIs.
Click here for full-size dyno sheet