For months you've been looking at the custom Magnaflow side-exit exhaust on Project SRT-4. And for months we've been trying to sort out testing it thoroughly enough to present meaningful results. This month we've got some answers. And we've added a few other goodies to the car in the form of a strut tower brace from DC Sports and a short shifter from Mopar.
MAGNAFLOW EXHAUST
We have to admit, the idea of exhausting spent engine fumes under the rocker panel just in front of the rear tire isn't original. In fact, it's more than 30 years old. Dan Gurney performed this feat on the 1970 AAR 'Cuda. And since Project SRT-4 pays some serious homage to that car, it only makes sense that its exhaust is similar. Fortunately, building a side-exit exhaust on the Neon chassis is very simple.
We took our car to Magnaflow and explained what we wanted. Three days later, we picked it up. Six months later, we got around to testing it. And now, nearly 10 months since this gorgeous piece first graced our SRT-4, you're finally getting to read about it. Aren't magazines great? We think so.
Project SRT-4's custom side-exit exhaust uses off-the-shelf parts from Magnaflow's catalog. The mufflerless system uses a resonator with a straight-through core and a 3-inch slash-cut tip. The rest of the system is 2.5-inch stainless steel and mandrel-bent tubing.
Magnaflow used a combination of 2.5-inch stainless-steel tubing, a 180-degree J-bend, a 90-degree L-bend and a 3-inch slash-cut tip to fabricate the exhaust. The new exhaust follows the stock routing until just in front of the left rear wheel. Where the stock exhaust zigzags around the gas tank, ours just ducks and shoots out the side. This configuration eliminates many feet of convoluted plumbing over the rear axle as well as the unnecessary dual-exit Dodge put in the smaller 2.25-inch stock exhaust, both of which should save weight and hopefully reduce exhaust backpressure.
To that end, Magnaflow used its 4x18-inch resonator, which has a 2.5-inch straight-through core to quiet the SRT-4's 2.4 liters. The perforated-core resonator contains rock wool, which is formed from molten volcanic rock. Magnaflow tells us this material can handle extreme heat but won't tell us how extreme. The hottest part of the resonator is also packed with steel wool. These materials won't degrade or break up like fiberglass. Since the stock exhaust also has only a resonator and no muffler, we figured this configuration would still be similar in noise output to stock. Exhaust backpressure is the enemy of the internal combustion engine. Reducing it makes it easier for exhaust gases to exit the combustion chamber, which reduces the amount of work the engine has to do to shove it out (pumping losses if you're an engineer). Less backpressure also means less leftover exhaust diluting the next intake charge, which means more gas, more oxygen and less heat. All of this means more power.
Reducing backpressure in most boosted engines has the additional benefit of better turbine efficiency, which results in better boost response and more boost. However, the SRT-4's active feedback boost control will cancel this benefit with more aggressive wastegate operation so the only gains would theoretically come from increases in pumping efficiency. Realistically, this means reducing backpressure on the SRT-4 engine should yield similar gains as it would on a normally aspirated engine-not nearly as great as on other boosted engines.
Measuring backpressure in the Magnaflow exhaust would give us some indication of how much more efficient it was and what, if any, power gains we could expect. And we didn't see any way the Magnaflow system could produce more backpressure than the stock exhaust.
We didn't see any reason the Magnaflow exhaust wouldn't make power after looking at it next to the stock exhaust. With biggertubing (2.5 inch vs. 2.25 inch) and a far less complex design, it also made less backpressure. | 
Magnaflow welded an exhaust hanger to the chassis just in front of the rear trailing arm mount. A small notch is required in the pinch seam at the side of the underbody to allow room for the exhaust to move around a little. |  |
Magnaflow's 4x18-inch perforated-core resonator uses rock wool and steel wool to reduce noise. The perforated core flowsessentially like a 3-inch pipe. | 
The SRT-4's stock exhaust can be removed just after the catalytic converter. Magnaflow used band clamps to attach the new exhaustto the stock pipe. | |