Richard Holdener
December 13, 2006
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.