The B7 RS4 must have been the very last German high performance car with conservative sound (and design). I just can’t understand why Audi muffled its 4.2L V8 so much.

I mean, isn’t the whole point of shoehorning a big V8 into a platform engineered for four bangers to advertise the hell out of it? Audi obviously gets it now, because everything with an RS badge comes standard with a crackling exhaust and pops at each DSG gear change. But being an older model, Project Quattro required some help.

That help came from the good guys at GruppeM, who recently took care of the intake sound.

This isn’t the first time I’ve fitted a GruppeM product to one of my project cars. The upgrade we did to Project Drop Top breathed more life into the engine and boosted performance to boot.

In the RS4’s stock form the intake sound is there, but you know it can be made so much better. By replacing the factory air box with GruppeM’s carbon fiber ram air intake system, we’d be able to unleash the creamy induction sound that all naturally aspirated V8s deserve to have.

The ensemble, which looks like something out the winds section of an orchestra, would not only give the V8 its rightful voice, but Momose-san at GruppeM said I’d get a little boost of power and response too.

That’s because every air box that Gruppe M designs is developed and thoroughly tested on a flow bench to guarantee that tangible performance improvements are made, while ensuring that the delicate relationship a high-revving NA motor has with intake back pressure isn’t meddled with.

Before the new system could be fitted, the factory system had to come out – something the mechanics at GruppeM were into minutes after the RS4 was brought inside the workshop.

While they started looking into that side of the process, I took some time to drool over the carbon fiber marvel that is the main air box structure itself. I’m a sucker for carbon, especially at this quality level.

GruppeM has been the official Japanese importer and supplier of K&N products for over 30 years, so it was no surprise to learn that their intake systems use K&N air filters.

The intake system has been designed to not only balance air intake pressure and air flow, but also shield the internal intake tract from engine bay heat.

If you were doing this install yourself at home, fitting is actually very straightforward thanks to a clear set of instructions, regardless of it being written in Japanese.

As this kit requires blow-by to vent to atmosphere rather than recirculate back through the intake, it also comes with a little K&N breather filter.

The first thing to come off was the air guide and the top half of the stock air box, which then gives you access to the filter – in this case an aftermarket K&N panel unit.

And a very dirty K&N panel filter at that.

Fitting the GruppeM air box to Project Drop Top showed how sensitive modern cars are when you start fiddling around with their electronics. I wasn’t sure if the same issue with the stock air flow meter position was going to happen to the RS4 seeing it was a whole generation older compared to the 2015 435i, but it is something you need to be careful with. In the BMW, the angle of the sensor was off by just a millimeter and it caused issues with stalling. That was quickly fixed with a different thickness spacer.

Looking at the two GruppeM mechanics do their thing, it became quickly obvious that even seemingly easy jobs often come with their own set of hurdles. There is always a stubborn nut or bolt.

With some persuasion, the other half of the factory air box eventually came off. You can see where the valve that opens at somewhere around 3,500rpm is located. This is there to create the right intake pressure at low RPM, while silencing the whole intake during gentle driving. GruppeM tests revealed that there is no loss in power, torque or response at lower RPM by removing this system.

One thing to keep in mind here is that stock air boxes aren’t bad, even on performance cars like the RS4. They are simply engineered and developed to function well at all throttle openings and RPM while keeping the intake muffled and refined. Aftermarket items like the GruppeM one are used to boost maximum power and flow irrespective of noise level and of course material costs.

With the old air box out of the way and the general area given a quick wipe down, it was on to installing the new shiny bits. The main air box dropped in place pretty smoothly.

It was then onto refitting the factory air flow meter (which had been removed from the stock air box), but not before it was given a careful spray clean.

A lot of care was also taken when inserting it into the new flange.

The intake pipe was then secured onto the stock rubber intake tube, and the larger side lined up with the K&N cone filter housed in the air box.

A large metal clamp was then added, securing it all tightly together.

The last few pieces of trim that were removed prior to the install were then screwed back in place and the installation was almost complete.

While the mechanics cleaned up their tools it was time for me to grab some images of the fresher-looking engine bay.

The GruppeM airbox looks so good in the engine bay; it gives a modern touch to it all and with one quick glance you know it’s as beautiful as it is functional.

Momose-san came over to take a quick look at the finished installation and to hear the engine breathe a little more freely and loudly.

After a quick test drive to warm the engine back up, a Bosch scanner was plugged into the OBD port to check for any errors. Anything out of the ordinary with the air flow meter or any other sensor/parameter would quickly show up, but there were no such issues.

Now we were all done and ready to go. But don’t worry – I’m not going to end this post without letting you hear what the thing sounds like…

The sound from inside the cabin has improved dramatically. I can finally hear the V8 induction at low RPM, and once it gets on song, well, it’s like a whole new car. But the best is the racket it now makes from the outside, and I had to get a friend to do a couple of fly-bys to illustrate this properly on video.

I am beyond ecstatic with this upgrade, but now I feel a need to improve the exhaust sound side of things, you know, for balance…

Dino Dalle Carbonare
Instagram: dino_dalle_carbonare
dino@speedhunters.com