Richard Holdener
December 13, 2006
Our never-ending quest for horsepower took us to MagnaFlow for an exhaust upgrade.

Here we are again, looking for ways to make more power from the '96 4.6-liter Two-Valve residing in the engine bay of Project Redheaded Step Child. Though we jumped the gun a bit in Part 1 by immediately testing minor bolt-on components, we stepped back in Part 2 and treated the 200K mod motor to some much needed TLC.

The list of high-maintenance components included new plugs, wires, and coil packs along with fresh Lucas synthetic oil, a new fuel filter, and an Accufab adjustable fuel-pressure regulator. We even replaced the well-worn accessory belt, something we noticed when performing the installation of the BBK underdrive pulleys. With the V-8 now ready for more power upgrades, we went to MagnaFlow for a few exhaust modifications-after all, what goes in must also come out.

Exhaust modifications rank right up there with mass air, throttle body, and pulleys in terms of popularity, and for good reason. They cannot only unearth additional power, but they also can alter the very character of the Mustang by replacing the mellow stock system with something altogether more menacing.

Given the relatively modest power output offered by the near stock, pre-PI mod motor, we were actually somewhat appreciative of the quiet demeanor. The last thing we wanted to do was draw unwanted attention from a nearby LS1, 350Z, or WRX. Don't get us wrong-if we pulled up next to them, it was most certainly go time. It just sucks to have to hope for wheelspin or a missed shift from your opponent in order to be competitive. Though the minor mods performed in Part 1 were worth a few extra ponies, we weren't even up to the power output of a stock PI engine, let alone one of the other more modern musclecars.

Last time out, Project RSC received a handful of basic bolt-ons, including a throttle body and plenum, a set of underdrive pulleys, and a custom chip. When tested at Powertrain Dynamics, the 200,000-mile 4.6 pumped out 209 hp at the wheels. Despite running on a DynoJet chassis dyno at both places, the power was down to just 199 hp in baseline form at MagnaFlow. We can't explain the difference in power between the dynos, but the new numbers repeated three times in a row and are a perfect example of why we reestablish a new baseline before we start swapping parts.

As luck would have it, the gang at MagnaFlow offered us not only a stainless steel performance after-cat exhaust for the '96 GT, but also a trick Tru-X X-pipe system. The Tru-X system was designed to replace the factory H-pipe. In 1996, Ford relied on no less than six catalytic converters to meet emissions. Not surprisingly, the use of six catalytic converters had a less-than-positive effect on exhaust flow. In addition to having to force the exhaust flow through the converters, the factory H-pipe also suffered from excessive tight-radius bends. The combination of the tight-radius bends and triple converters (per side) made us look forward to replacing the stock system with the much-improved Tru-X system offered by MagnaFlow.

Though not technically an emissions-legal part, the car will pass the sniffer portion of the stringent California test (we know this for a fact), if not the actual visual portion. Only a performance-savvy inspector will likely catch the X-pipe, since the MagnaFlow system did feature (obviously effective) catalytic converters. We liked the idea of having the cats in place since enthusiasts should continue to do their part to keep the air clean. Performance and reduced emissions are not mutually exclusive. Given the power gains offered by the replacement of the factory cats, we'd say there is probably little power left to be had from the removal of the two remaining cats-that is, until we step up the power level with cams, ported heads, and a new intake. We'll be taking a look at long-tube headers and a cat-less X-pipe in the near future, but for now, we like the idea of being clean and mean.

Installation of the Tru-X system was easier as a two-man job.

The MagnaFlow Tru-X system was a direct bolt-on replacement for the factory cat pipe. In addition to the stainless steel construction, the Tru-X featured provisions for the four oxygen sensors (before and after the cats). The system bolted to the factory exhaust manifolds and even relied on the factory mounting brackets (on the tranny mount).

After the installation of the new Tru-X system, we were instructed to take the car out for a quick drive to burn off the coating applied for shipping and storage. The power gain was immediately evident from behind the wheel. We were impressed that the power seemed to be better everywhere, not just at high rpm. The Dynojet verified what our backsides were telling us, with the peak power up by 11 hp, from 199 to 210 hp. Elsewhere along the curve, the power gains were up by as much as 12-13 hp. The torque gains were equally impressive, with the peak up to 281 lb-ft from a maximum of 268 with the stock cat pipe.

Given that the factory cat pipe was the restrictive component in the exhaust system, we expected little power gain from the axle-back exhaust. Taking nothing away from the impressive MagnaFlow performance after-cat exhaust system installed on our '96 project car, the reality is that even having no system would be of little benefit at the current power level.

Here is the finished installation of the X-pipe on Project RSC.

That said, the reason behind the installation of a new after-cat exhaust is more than just power. While the Tru-X cat pipe offered a slight change in the exhaust note, the real change came once we installed the new MagnaFlow stainless steel after-cat. We know the flow gains offered by the MagnaFlow will come in handy once we up the power output with cams, ported heads, and a new intake, but for now we would be satisfied with an improvement in sound quality.

The new system offered stainless steel construction (to ensure a long life), ease of installation (things were well labeled and fit as promised), and a throaty (but not overly obnoxious) sound quality. The kit came complete with everything needed to perform the installation, including a pair of different exhaust-tip mounts to work with the different model years. The polished mufflers were almost too nice to install under our high-mileage machine.

With our new system ready to install, the MagnaFlow guys made short work of removing the factory exhaust.

After the installation was completed, we took the car around the block again. There seemed to be a few extra ponies there. Sure enough, the dyno indicated that the MagnaFlow after-cat offered roughly 4-5 hp, peaking at 214 hp and 286 lb-ft of torque. That was certainly more than we bargained for-a pleasant surprise.

All totaled, the trip to MagnaFlow upped the peak power output of our project car by 15 hp and 18 lb-ft of torque. Though 300 rwhp was still a ways off, we were that much closer to our goal. Next month we hope to step up to PI power levels with the installation of a set of Xtreme Energy cams.

Stock Cat Pipe vs. MagnaFlow Tru-X Stock
Naturally, the stock exhaust system on Project RSC left a little something to be desired, both in terms of aural appreciation and absolute airflow. Coming to the rescue was MagnaFlow in the form of its Tru-X X-pipe. Being environmentally conscious, we elected to retain use of the cats. At the 4.6's current power level, the cats weren't costing us much in the way of power, especially since we had yet to install a set of long-tube headers (they are coming). The power gain offered by the MagnaFlow Tru-X was immediately apparent from behind the wheel. Testing on the DynoJet confirmed the seat-of-the-pants suspicions, as the Tru-X system improved the peak power output by 11 hp, (from 199 to 210 hp). The peak torque jumped from 268 to 281 lb-ft.

Stock After-Cat Exhaust vs. MagnaFlow
Given the relatively low power output of our test motor, we were actually not expecting too much power from the MagnaFlow after-cat system. The reason for our relatively low expectations had nothing to do with the quality or design of the MagnaFlow system and everything to do with the laws of physics. The greater the power output of the motor, the greater the exhaust flow (a 300hp motor will produce more exhaust flow than a 200hp version).

Contrary to popular belief, the factory after-cat exhaust system is pretty effective, especially at near-stock power levels. The farther away you get from the factory power rating, the more restrictive the factory exhaust becomes. Given that the cat pipe is the major restriction in the factory exhaust, changing the after-cat was more a preparatory measure for future power levels than an expectation of huge gains. True to form, the MagnaFlow after-cat was worth a few extra horsepower, upping the peak power output to 214 hp, bringing our total gain to 15 hp (more power was actually realized elsewhere along the curve). As we said in Part 1, a little here and a little there-it all adds up.