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Project SRT-4: Part V

Side-exit exhaust and other Gismos

Dave Coleman
Dec 21, 2005
0408_01z+dodge_srt_4_sedan+front_right Photo 1/16   |   Project SRT-4: Part V

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.

0408scc_neon_02_z Photo 2/16   |   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.

0408scc_neon_08_z Photo 8/16   |   Inspiration for our side-exit exhaust comes from the 1970 AAR 'Cuda. Year One, Inc. sells the original replacement exhaust tip for that car. Based on the shape of this tip, it looks like the 'Cuda had a far more convoluted exhaust routing than our car does.

As far as we know, no one makes a tool to measure exhaust backpressure, so we built our own. We started with a glycerin-filled, 4.5-inch, 30-psi pressure gauge from McMaster-Carr (www.mcmaster.com, part number 3708K402). We then took an 18mm fine-thread bolt that happens to have the same threads as an oxygen sensor, some copper tubing, a few brass compression fittings and some vacuum line. Voila! Instant backpressure gauge.

We had a machine shop drill and tap a hole in the bolt for the brass fitting. Then we attached a few feet of copper tubing to the fitting, followed by several feet of rubber vacuum line leading to the gauge. The copper tubing can handle high-temperature exhaust gases and the rubber line allows you to put the gauge wherever you want during testing. All our testing happened on the dyno so we just ran it under the car and in the passenger door.

We removed the first O2 sensor and installed the bolt and brass fitting in its place. This allowed us to measure backpressure before the catalytic converter. If you're smart, you'll zip-tie the O2 sensor out of the way before you start the car. If you're like us, you'll let the zip-tie short out on the alternator's positive terminal and then burn yourself when you try to remove it. Remember, O2 sensors are heated. Heat will burn you.

When you're done burning yourself on the O2 sensor, you'll realize it would be really nice to know how much backpressure there is after the catalytic converter as well as before it. This would give you some idea how much of a plug the cat is and allow you to judge how much power might be found by replacing the factory cat with a high-flow piece from a company like Magnaflow. Many modern cars put the second O2 sensor after the cat. In those cars, this would be easy to figure out, but on the SRT-4, the second O2 sensor is in the middle of the cat between the two blocks, making this test worthless. Apparently, our friends at the California Air Resources Board mandate this placement so we can blame them for making the test impossible.

0408_09z+dodge_srt_4_sedan+exhaust_tips Photo 9/16   |   Before and after. Perhaps the only drawback to a side-exit exhaust is that the tip lies directly in the debris path of the drive wheels. That means every piece of sand and grit kicked up by the front tires hits the shiny Magnaflow tip. Below is what a new tip looks like. On top is our tip after about six months of use. Note the shiny one is much longer. None of Magnaflow's 3-inch slash-cut tips are short enough, so we had to cut it short.

On the dyno, the Magnaflow exhaust made 5.3 psi of backpressure, while the stock one made 7. The improvement is actually slightly better at the exhaust ports, though. The turbine creates a ton of backpressure (we're told it's more than 35 psi), but here's the magic: the pressure ratio across the turbo stays the same when we change the exhaust. If you add atmospheric pressure, the pressure in the manifold is about 50 psi (35 psi plus about 15 psi atmospheric pressure) and downstream at our pressure gauge, it's 22 psi (7 plus 15), so that's a pressure ratio of about 2.25:1. Now, take 2 psi of backpressure out of the exhaust, as we almost did, add atmospheric pressure back in (5 plus 15 plus 20 psi) and multiply by 2.25 and you get 45 psi. Subtract atmospheric pressure again and you only have 30.5 psi in the manifold now.

If you got lost in all that, here's the point: We lost 2 psi in the exhaust, but lost 4.5 psi in the manifold where it matters. Hurray for turbos! On our dyno, the exhaust was worth 4 hp and 4 lb-ft of torque at the wheels. The final numbers are 239 hp and 261 lb-ft of torque with the Magnaflow exhaust.

Before trying this kind of dyno testing yourself though, you need to know one more thing about that ECU-controlled boost. A sudden drop in backpressure from the new exhaust will cause a sudden spike in boost, which will scare the ECU and pull all your boost away. Over time, it will give your boost back, but you have to teach it by driving hard. We found two fourth-gear pulls on the dyno were enough to rebuild the boost map. A fourth-gear pull to redline on the freeway would do the same thing, but we're not that stupid.

0408scc_neon_14_z Photo 15/16   |   The shifter is bolted to the floorpan with four bolts. Remove those and the shift-cable ends and it comes out.

MOPAR SHORT SHIFTER
The boxes just keep showing up from Mopar. And the latest one contained Mopar's short-throw shifter for the SRT-4. This self-contained piece is a direct replacement for the stock shifter. Getting the old shifter out requires removing the center console. It's held in place with four screws in the bottom of the armrest container and one more in each cupholder. Then it's a wrestling match to get it out over the emergency brake lever.

The shifter housing is held to the floorpan with four bolts. The cables are removed with a serious tug and are held in place by interference-fit bushings. The Mopar shifter looks virtually identical to the stock shifter with one exception. Its pivot point is relocated an inch or so higher on the housing, dramatically changing the length and effort of each shift throw. You'll need a new shift knob, as the stock knob is designed for one-time use. Once it's been removed, the metal clip that holds it in place is permanently bent. It will go back on, but the next time you try to rip second gear, it'll fly off and smack your rear-seat passenger in the head hard enough to leave a lump. Expect about 30 minutes to install the shifter if you've ever previously run a wrench.

The shifter does exactly as Mopar claims-shift throws are significantly shorter. But you rarely get something for nothing. With the shorter throws comes a serious increase in effort. Thanks to this side effect, we don't think the shifter will actually speed up your shifts. And it takes some getting used to, but we find ourselves enjoying the shorter throws and spending less and less time worrying about how hard it is to move the lever. Besides, our spindly editor arms can always use the workout.

We have found it slightly easier to downshift to second gear. With the stock shifter, we found ourselves struggling to find second gear occasionally. So our verdict is positive. The Mopar short shifter is different, better and reasonably priced at about $100.

0408scc_neon_16_z Photo 16/16   |   We've always thought strut braces are as much eye candy as they are function. DC Sports' CS-2 strut brace is a terrific-looking powder-coated steel piece. Plus, it fits with our car's Ground Control camber plates.

DC SPORTS STRUT TOWER BAR
The Neon chassis is flexible. Don't pretend it's not. As Project SRT-4 gets stiffer and more responsive every month, the shortcomings of DaimlerChrysler's small-car platform become more and more obvious. In its current configuration (Mopar Stage 3 coil-overs, Prothane bushings, 17-inch wheels and tires), the platform feels about as stiff as Bob Dole before Viagra.

If there were a billet floorpan brace available for the SRT-4, we would install it-this chassis needs all the help it can get. But there's not. So we have to settle for something almost as good. DC Sports' CS-2 steel strut tower brace for the SRT-4 is designed to reduce lateral chassis flex under hard cornering loads. It bolts to the strut tower using the upper strut mount bolts. Our car has Ground Control camber/caster plates in the strut mounts. We found that the Ground Control bolts are long enough to safely secure the brace to the chassis.

We can't feel a huge difference on the road, but we figure bracing a known weak area can't hurt. Plus, at a relatively lightweight 7.5 pounds and a retail price of $115, what can it hurt??

Sources

DC Sports
City of Industry, CA 91746
800-237-7560
http://www.dcsports.com
Mopar
Auburn Hills, MI 48321
800-992-1997
www.mopar.com
MagnaFlow
Rancho Santa Margarita, CA 92688
800-824-8664
www.magnaflow.com
By Dave Coleman
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