Technical Features
Installation: Milltek Exhaust for B7 RS 4
By by: Anthony Garbis, photos by author
Jul 6, 2007, 08:26

Modifying a rare, ultra-high performance automobile is tricky business. This is especially true for the RS 4, as engineers at quattro GmbH outdid themselves developing the car: 19-inch wheels, 14.4-inch front cross-drilled rotors with eight-piston calipers, dynamic ride control and of course the high-revving (8,250 rpm) 420hp 4.2l V8 FSI engine. With a platform that has already been extremely tweaked, what else is there left to do?

When this 2007 Imola Yellow RS 4 was added to the fleet of cars owned and driven by Fourtitude staff, our first thought was to turn it into a project car. However, the B7 RS 4 represents the first time we’ve wondered if there’s enough room for improvement to warrant a project series.

Especially in its bright gold hue, the car attracts a lot of attention. People often comment on the car and ask what has been done to it – those same people are astonished to hear that the car remains basically the way it comes from the factory. With an integrated spoiler lip, wide fender flares and an aggressive front bumper, there are few aftermarket cosmetic enhancements to be had here.

Certainly we could change some cosmetics for subjective tastes, and we’ve thought of changing to another set of wheels. However, with 19x9” wheels, that’s easier said than done. Most other wheels for Audis are only 8” in width – a downgrade in performance of sorts, though they might make it easier to slide around.

For now, we’ve decided to utilize the RS 4 for a small series of technical articles. With a limited number of modifications planned for the car, this seemed the best route. And, having heard the sultry tone of Champion Racing’s demonstrator RS 4 at ALMS races, with its straight exhaust, we were inspired to begin with the car’s audible tone, and maybe even adding some more power.

Compared to the S4, the RS 4 exhaust note is mellower at idle and low engine speeds due to "flappers" in two of the four tailpipes. Although the tips on the RS 4 are oval, there are actually two distinct tailpipes coming out of each muffler. The innermost tailpipe on both mufflers contains a vacuum-controlled valve that is closed when not in sport mode, or when the engine speed is below 5,000 rpm. While this is nice for quiet drives around town, it doesn't fully embody the performance aspect of this car. Granted, sport mode does create a more aggressive exhaust note, but that note is still somewhat reserved.

It was a quick search for a replacement exhaust, as we already knew what we wanted. Milltek exhausts are known to be more aggressive than factory, but maintain an OEM look and exceptional production quality. Milltek offers both resonated and non-resonated center pipes, and the mufflers retain oval exhaust tips, though they curve with the bumper - something the factory exhaust should have done. Milltek even tailored their exhaust one step further and offers mufflers that incorporate new valves.



In love with the sound of that silver RS 4 we’ve been seeing at ALMS races, we decided on a valved, non-resonated system. The valved systems command a $1,000 price premium; however the ability to control the exhaust level is one that we did not want to lose. It may seem odd that thus far the focus has been on sound rather than power gains, but when you have 420hp, how much more do you need?

Well, that is a silly question - there is never enough horsepower! However, power increases weren't the primary goal with the exhaust system. With that said, we headed out to DTM Motorsport in Dulles, Virginia for a baseline dyno run, the exhaust install, and a post dyno.

This method of testing was chosen because it would show the horsepower and torque gains from the exhaust without having to worry about different dynamometers or temperatures. DTM Motorsport has an all-wheel drive 500 series Mustang Eddy Current Dynamometer, which is one of the few in the mid-Atlantic region, and they were kind enough to squeeze the RS 4 in for a Saturday morning appointment.

Upon arrival, the shop promptly put the car on the dyno and did two pulls. The results were virtually identical on both runs, with the best pull reporting 284.3 wheel horsepower and 240.6 wheel torque. If the engine does in fact produce an Audi claimed 420 horsepower, then this would show a staggering 32.3% drivetrain loss. It is also important to mention that generally Mustangs read lower than Dynojets, and configuration differences on Mustangs will produce different results. It's not viable to look at two separate cars that have been measured on two separate dynamometers, as it would be like the comparison of apples and oranges.

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With the baseline dyno run complete, it was time to get the car on the lift and remove the stock pipes. The factory exhaust unit is all one piece, and there is no good location to cut it. Make sure that you plan accordingly to take the exhaust, once removed, home with you; we had to go to U-Haul and rent a cargo van in which to fit the piece in its entirety. Removing the exhaust is rather simple since there are two clamps on each pipe that connect the rear section to the catalytic converters, then four sets of hangers to unhook. The tricky part will be removing the one-time use clamps that secure the vacuum lines to each valve system.



With the factory exhaust removed, it was now time to start piecing together the Milltek system. The Milltek solution is in three parts: a small cross section that connects to the catalytic converters, two mid-pipes (resonated or non-resonated) and two mufflers (valved or non-valved).



For a shop with a lift, the whole removal and install process should take less than an hour, with the most time consuming part of the process lining up the exhaust tips and tightening down all clamps. Securing the vacuum lines can be done with hose clamps, or even easier, just two zip-ties.



With the Milltek exhaust now fully installed, we were ready to hear it. Firing up the car, a deep roar filled the shop. We quickly moved the car to the dyno and performed a run. The first pull was not much higher than the stock run, which showed that the ECU hadn’t had enough time to adapt to the freer flowing system, so we drove the car on the dyno for a few minutes, and then performed a second pull. This next run resulted in consistent power gains across the whole power band, with a peak wheel horsepower of 293.1 and 252.3 torque - a gain of 8.8 horsepower and 11.7 ft/lbs of torque at the wheels.



At first, the drastic change in sound was a little daunting; however after a day or two, you'll probably agree that this is the way the car should have come from the factory. Mid range sound is throaty and the top end truly screams.

Previously, under full load and when not in sport mode, all you would hear is engine noise (at least from inside the cabin). Now you hear a perfectly matched exhaust note. The exhaust is a little loud between 1400 and 2100 RPM, but with the windows up, not much makes it into the cabin thanks to the RS 4’s sound insulation. There have been numerous passengers in the car since the exhaust install, and many have commented on the nice sound. None of complained that it's too loud or intrusive.

With a valved Milltek system like the one on our RS 4, the exhaust truly opens up once you activate sport mode. Combined with the non-resonated center pipes, the flappers are needed to keep city driving tolerable. While switching between sport mode and regular mode, we’ve found that the flappers reduce about 20-30% of the noise between 1400 - 2100 RPM.



While this may not seem like much (20-30%), the difference is very noticeable. Although the exhaust sound with the flappers open at low engine speeds is bearable, we feel that after a week or two it would become an annoyance, not to mention passengers that may find it too loud. Fortunately sport mode allows you to decide when and when not to run at this audible level.

On the highway, sport mode is absolutely amazing; words can't accurately replicate or describe the sound. We couldn't be more pleased with the performance, look, and sound of the Milltek valved cat-back exhaust system on our RS 4.

If you are looking for a Milltek exhaust for your RS 4, but don't want to spend the extra money for the flappers, then we'd strongly suggest the resonated mid pipes and non-valved mufflers – retailing at $1,899 (resonated systems are $200 more than non-resonated systems). However, compared to the price of the car, $1,000 doesn’t seem like that much money to retain full sport mode functionality and the ability to increase or decrease the exhaust sound. Do it once and do it right - you won't be disappointed.

LINKS:

www.DTMmotorsport.net www.MilltekSport.com www.Stratmosphere.com

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