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Rob’s Completely Custom Audi B6.5 RS4 Avant

What a B6 RS4 Would Have Looked Like, If Audi Built It...

Do you love long-roofed Audi Avants (wagons)?

Do you love the B6 body style, particularly the rear end?

How about the gorgeous lines of B7 RS4 with its bulging fenders and classy front-end?

Combine these ingredients and you have the world’s first “B6.5” RS4 Avant.

Rob Aguilar of Vancouver, Washington set out on this build to do something totally different. While many people had built B7 RS4 clones, and some even went as far as to build B7 RS4 Avants in the US, the real difference is that this car intends not to be a B7, but retain some of the B6 characteristics to imagine what it’d be like if Audi ever built a RS4 before the 2005.5 body style rolled out.

Rob himself states it best when explaining his goals for the build:

My goal, again, was not to build a “B7 RS4 Avant clone”—-that car has already been built; no—-what I wanted to build was a car that Audi never created, or at least a transitional platform: what I call a “B6.5”. I wanted to see what it would look like if Audi had ever built an RS4 on the B6 platform—-not the B7—-or again, at least a transitional platform, that blends in various elements of both platforms. And yet everyone who sees it swears it looks OE—which of course was the entire point. Parts were sourced from the UK, France and Belgium—-took me about 9 months to gather it all (notice the front and rear bumper covers—-no corner markers like US-spec).

The main differences from this and a B7 RS4 clone is the B6 rear end, specifically the tail lights & tailgate are entirely different, as well as more subtle things like the B7 fuel door is larger and in a slightly different location, and most importantly; the B7 body line is different and more curvy, whereas the B6 has a straight, clean, uninterrupted body line. The B6 doors are also slightly flatter, and a few other elements, that involved more custom work to pull off but also gives the car a different (and cleaner?) look. 

To maintain the B6 body lines and work with the B6 doors, Rob’s team had to pound out the B7 body line on the aluminum RS4 fenders and build a B6 body line onto them so that it would match from front to rear. It took countless hours to get it right, but it came out super clean and OEM. The rear doors also had to be flared out to blend in with the rear fenders, which was no small feat.

Even more challenging was getting the rear bumper to be integrated. The B6 and B7 Avant rear tail lights are mostly identical going from the top-down about 5 or 6 inches, but the B6 ones were much taller and larger than B7, presenting a serious challenge.

To make it work, the B7 RS4 rear bumper cover had to be cut down to fit underneath the bottom of the much larger B6 tail lights, then a shelf had to be built on top of the bumper to go underneath the bottom of the tail lights. 

Another challenge was the bottom outside corners of the B6 tailgate are more squared off than on a B7, so custom work had to be down to cut down the B6 rear tailgate had to be cut down and get welded back up underneath to be rounded off enough to work with the B7 RS4 rear bumper cover.

There were a number of smaller items that had to be done too, ranging from the underbelly pans to headlight plugs. You can read more about it in Rob’s build threads which goes into extensive detail.

The end result is nothing short of incredible in both it’s attention to detail and how everything worked out.

The more you know about Audis, the more you are likely to appreciate it…so it’s no surprise it won “Best Audi in Show” at the 034 Motorsport Summerfest this past year.

By now you’re probably saying “ok, ok great job on the body – but it’s not a real RS4 conversion unless you also updated the engine.”

Fear not my friends, Rob is two steps ahead of you.

Rather than going with a B7 RS4 engine, Rob again wanted to something a little different and a throw back to some of the best options in previous S4/RS4 generations. Rob chose the 2.7L twin turbo engine instead, best known for being used in the B5 S4 but also featured in the A6, Allroad, and a few other applications.

This 2.7L TT motor is capable of much more power than the V8 it replaced, and it also doesn’t have the carbon build-up issues associated with the B7 RS4 motor, either. While the naturally aspirated V8 sounds amazing, it is somewhat limited in its ability to add power, and even super expensive parts like superchargers add a fairly nominal amount of power.

Rob’s B5 S4 twin turbo engine conversion, on the other hand, is running the XSPower Stage 3-plus system at about 493hp. This is quite a bit more than the RS4 motor of either the B5 or B7 generations.

I’ve driven Stage 3 2.7L TT engines and I have to say it’s among the most thrilling of any car I’ve driven, yet alone of an Audi…and the ability to add power is near limitless. The only downside is that the motor can be a bit high maintenance and changing out things like the water pump is quite the chore, but no high horsepower engine isn’t without its quirks and downsides.

On the inside, the modifications are slightly more subtle and minor.

Most noticeable is the rear seat delete and the custom diamond plating throughout the rear. Cargo room galore!

I asked Rob about the rear seat delete as it is a bit of an unusual mod in a station wagon, but he said the rear seat was never used and the weight savings was substantial – and on top of that, he was able to build custom storage into the false floor to hold detailing supplies, make it more practical too.

The car also has a custom stereo, carbon fiber trim throughout, and will eventually have custom Recaro front seats to assist with both weight savings and keeping the buttocks planted through hard cornering.

Rob supplied a mostly complete mod list below, but this is a car that he’s owned for years now and has had so much custom work this list is far from exhaustive:

Engine Mods:

  • Full 2.7T conversion
  • XSPower stage 3+ upgrade: K04/025/026 turbos with RS6 hotsides; larger MAF; custom CAI; RS6 all aluminum IC’s
  • Rowetech Stage 3+ tune
  • Custom-made, mandrel-bent full 3″ downtubes by GBE Exhaust, Portland
  • Custom made, mandrel-bent full 3″ exhaust by Stan’s Headers, Auburn
  • Dynomax stainless mufflers, Vibrant Performance stainless resonators and Redtail tips
  • South Bend Stage 2 “street” clutch
  • 034 Motorsports Carbon Fiber RS4 intake y-pipe

Wheels & Suspension:

  • Bilstein PSS9 coilovers
  • Stern adjustable upper control arms
  • RotorLab 18Z brakes up front, cross-drilled rotors front and rear
  • VMR V810’s in 19×9.5 ET25


  • One-of-a-kind complete “B6.5” RS4 body conversion, using all OE parts sourced from the US, the UK, France and Belgium (European front and rear RS4 Avant bumper covers that have no sidemarkers, etc)
  • DeutshceTek rear wing
  • Roof rail delete
  • Handmade black acrylic front splitter


  • One-of-a-kind permanent rear seat delete
  • UK Sounds rear OE-lookalike sub box
  • Full carbon fiber interior trim package
  • Handmade diamond-plate aluminum Audi Sport-emblazoned floor mats

Weight Loss:

  • Rear Avant crossbar, gone: 52lbs
  • Roof rails, gone: app 12 lbs
  • Rear seat, both pieces, gone: 128lbs, replaced by permanent rear seat delete project, weight 18lbs, net loss of 110lbs
  • Factory B6 S4 spare n tire: 56lbs, gone, replaced by 2009-only B8 19″ steel spare (17lbs), net loss of 39lbs
  • B5 S4 motor conversion resulted in a 45lb weight savings
  • VMR Flow Forged wheels – 11lbs unsprung weight
  • More planned (lightweight seats, etc.)

Personally what I love about this build is two things.

Firstly, the passion of the build – it’s clear from the way Rob documented and explained everything that an obsessive level of detail went into every single decision and modification that went into the vehicle.

Secondly, the vision. It would have been much easier, and cheaper, to build a B7 RS4 clone, or to just flare out the fenders on a B6 and call it a day. By envisioning this B5/B6/B7 hybrid he was able to achieve an OEM look without being limited by trying to follow a playbook Audi had already done in Europe or otherwise.

I also like that he was willing and able to take risks. The rear seat delete isn’t something for everyone, nor is the custom hood vents…but Rob didn’t build this to please others, he built it for himself, and to follow-through on his vision.

Last but not least, a car like this is never done. Rob tipped me off on a few custom touches he’s working on, that I’ll probably go back and update this post on when they’re complete.

I think this may be the best B6 ever built.

What do you think?

In terms of partners for the build, Rob would link to thank Aaron and his crew at Vicious Custom Auto Body in Fairview, OR for the expert craftmanship in turning his B6.5 RS4 dreams into reality, and obliging with his passion for details on things like the doors, flares, and rear hatch. Rob would also like to thank Ceder Rowe and his crew at Rowetech in Portland who did the 2.7T conversion and custom tune to make the most out of the power plant.

Nick Roshon

Nick has been an Audi owner and fanatic for the last 10 years, and started Nick's Car Blog in 2009 to share DIYs and pictures of his A4. Currently he drives a 2012 Audi TT-RS, and has previously owned a B7 S4, B7 A4, and an 82 Audi Coupe (GT) LeMons race car. In his day job, Nick is a digital marketer and lives in San Diego, CA, USA.

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