Tom Wilson
January 4, 2007

Horse Sense: If the name Jason Cenora rings a bell, it's because his SN-95 Mustang project car is a multi-time 5.0 Mustang & Super Fords feature vehicle. The most recent appearance was the Sept. '06 issue ("Waxing the Competition," p. 78).

Not long ago, you were a hero if you could make a small-block Ford churn out 500 hp. Now, 600 hp is off-the-shelf, thanks to warehouses full of deep-breathing air-management parts. We can now add two big-diameter exhaust kits from MagnaFlow to all the intake manifolds and headers.

We say two kits, but it really boils down to one exhaust system purchased in two parts. The first is an X-shape crossover-offered with or without catalytic converters. The second part is an after-cat exhaust.

The Tru-X crossover pipe is 2.5 inches in diameter and built from stainless steel. Unlike other X-shape crossover sections, the MagnaFlow pipe is not necked down, but measures a minimum of 2.5 inches at its inlets and exits, with plenty more between its smooth bends. When customers want catalytic converters with its kit, the company fits a pair of their own manufacture. Due to the amount of reactive material used, these cats are typically smaller than stockers, but they offer the same emissions-reducing capability.

We should stress that while the MagnaFlow Tru-X crossover with catalytic converters is an efficient emissions control device, it does not carry a California Air Resources Board Executive Order (CARB E.O.) number and is not a street-legal replacement part; the non-cat Tru-X is also not street-legal. But, the catalytic version will pass a sniff test and shouldn't lead to further investigation should anyone look under the car. Legalities aside, it scrubs the exhaust and reduces pollution so we can all breathe better.

The MagnaPack after-cat is a new design from MagnaFlow. The pipe diameter is 3 inches throughout, with mandrel bends. The mufflers are also MagnaFlow's newest straight-through constructions, measuring 5 inches in diameter. These low-restriction mufflers are designed to get you around on the street, but the MagnaPack name denotes MagnaFlow's more liberal sound-suppression standards. They're noisier than MagnaFlow's replacement street systems, which makes them better to support high-powered hot rods.

As an enthusiast's street system, the MagnaPack mufflers are polished to a mirror finish and fitted with carefully styled polished tips.

The Tru-X and 3-inch MagnaPack are aimed at the performance market, so the best way to test them would be on a hot rod moving big air-for S197 Mustangs, that means forced induction. Jason Cenora offered his '06 Mustang GT project as our demonstrator.

Among other things, Jason's car is destined for SEMA show duty, and therefore leads the hyper-hectic existence on which racers and show types thrive. He brought it to MagnaFlow's test center immediately after an all-night Novi 2200 installation at Eric Cheny's XMP skunkworks. It was strapped to MagnaFlow's Dynojet inertia chassis dyno for baseline runs, put on the lift for the quickie installation, and then went back onto the dyno for the after tests. The test on the intercooled blower installation consisted of a 30-mile drive from XMP to the test center, and the tune was strictly the over-the-counter software programmed in by the Paxton kit. The car had less than 300 miles on it when it was driven through the door.

Predictably, the baseline runs were simple. The first pass netted just below 400 rwhp. The second gained a couple of horsepower as the engine's oil warmed up, reaching exactly 400 rwhp. The third run dropped 3 hp as the cylinder heads started to heat soak, which is a typical response.

We're not sure what you think of 400 rwhp with the blower, which was pullied for 12 pounds. At 115 hp more than what these engines make stock on Dynojets, we think it's fine. The boost was about a pound lower than the nominal dozen psi, but we're not completely sure, because the boost gauge wasn't working during the baseline runs.

With the baseline in the bag, the project progressed to the MagnaFlow installation. Luckily, it was a fairly easy task because the pieces bolt on. We've been around several S197 exhaust installations and continue to marvel at the simplicity and ease with which the exhaust can be changed on these cars. We give credit to Ford for using high-quality clamps and an easy layout of the S197 exhaust.

Building these pieces uses a technologically advanced process. MagnaFlow's computer-controlled benders consistently produce accurately bent pipes that fit well. The Tru-X pipe section uses the ball and socket joint at the manifold end. Since the tubing is made so well and the X-section is welded in place, it pops in. If you have stock exhaust manifolds, you'll revel at the ease of fitting the Tru-X up to Ford's studs. The only tools required to hang the X-shape crossover are a socket and long extension.

The mufflers go on next. With MagnaFlow's new, 5-inch diameter mufflers, there is a lot more room around the round units as opposed to the stock oval ones. The separate exhaust pipe sections between the X-shape crossover and mufflers go on last. With all pieces fitted, the MagnaFlow techs snugged the hardware, adjusted the hang and angle of the pipes, and then tightened the nuts and bolts. Jason checked the fit of the tailpipes and wanted the driver-side pipe adjusted. This was accomplished by loosening the hardware, making a bump adjustment, and retightening. Thanks to the "no crush" design of the clamps, the adjustments are easily done with no worries about leaks.

From the install bay, we went to the road for a quick couple of blasts. This confirms the exhaust is tightly installed and not hitting the body. It is also a good way to check the heating of the catalytic converters and initiate the emissions control process, which makes the engine management in the S197 calm down. The test gave us an earful of the system's sonic qualities. It was, as most MagnaFlow designs, quieter at stock than we thought it might be, but it did belt out the tunes in a mellow roar when the throttle opened. If you're looking for a throbbing, drum-banging, buckshot-shooting exhaust, the MagnaPack is not what you want; it sounds more like a tuned horn.

Then it was back on the dyno for the after tests. A quick glance at the results showed a 12 rwhp gain at the peak. A closer look showed the freer-breathing Mustang making power, but at 3,800 rpm. It dropped below the stock output's trace of 5,000 rpm. It lost considerable power from the midrange to almost the peak before spiking out the 12hp gain at the end.

Another look shows the air/fuel ratio was a full point richer during the after-runs than during the baselines. Considering the baseline runs were at the ideal mid- to high-12:1 range, that means there was a power loss. The after-runs were also "dirty," meaning the horsepower curve was not a smooth line, but a series of jagged sawtooths.

MagnaFlow's Tech Center boss Richard Waitas explained the cause of this. His read on it was that the larger exhaust was allowing sufficiently more airflow (coupled with the supercharger) to take the computer out of its "comfort zone." That happens when the airflow is beyond the look-up tables with which the computer is programmed. Knowing only that it is running too lean-but not how lean-the computer compensates by adding extra fuel, which causes it to run rich and pull out fuel. This causes the engine to run lean again, and you have a repeating cycle of rich and lean with a corresponding sawtooth pattern in the powerband.

Unfortunately, we had no way of tuning the system at that moment, so we had to conclude the test knowing the MagnaFlow exhaust parts increase the airflow, but it will take electronic tuning to make use of it. On that judgment, the 3-inch-diameter after-cat and Tru-X crossover pipe appear worthy additions to supercharged Three-Valve Mustangs.

Our final advice is to shop carefully for this system, as the pricing reflects the high-grade material and mandrel bends. We'd also suggest MagnaFlow's standard 211/42-inch after-cat as the proper choice for naturally aspirated late-model GTs. That'll save some money and offer a quieter and more pleasant street-driving experience.