When it comes to tuning in the Volkswagen, Audi and now Porsche world, one name stands out above the rest. APR LLC, which was originally founded as “Auburn Parts and Repair” in Auburn, AL, has continued to blend performance with functionality since the shop began tuning Audi A4s in 1998. Since then, their market has expanded to include Volkswagen Seat, Skoda and Porsche, and the company now has a presence around the globe.

While Volkswagen doesn’t have an “official” tuning partner, APR is as close as the automaker gets. The first collaborative effort between the two companies was the Volkswagen GTI built for the 2006 SEMA show, and prominently displayed in APR’s lobby. The relationship continues to this day, and APR is currently at work building a murdered out Jetta, dubbed “Darth Vader,” for Volkswagen U.S.A.. While most dealers will point out that modifying your car’s ECU will void the warranty quicker than you can say “reflash,” APR has established itself through VW dealers across the country (and across the world), helping to legitimize APR’s software and hardware products.

Unlike most tuners, APR is a massive operation with an impressive amount of in-house capability. Everything from design through rapid-prototyping is done in house, and manufacturing is only farmed out when it can be done better by a third party manufacturer. A good example of this is the company’s Carbonio intakes and their stainless exhaust systems; since APR doesn’t want to lay up carbon fiber or bend stainless tubing in house, they farm the component manufacturing out to companies who can meet their exacting standards.

In fact, “exacting” may be an understatement. APR’s Opelika, AL facility includes a chassis dyno (in its own dedicated environmental chamber), a UV-curable resin rapid prototyping system, several CNC machines, fuel injector testers and even a high-pressure fuel pump test rig, the only one of its kind outside of a major automaker or tier 1 supplier. Buying a commercially available unit would have cost in the neighborhood of $500,000, so APR designed and built its own in house, for roughly $60,000.

That kind of “do it yourself and do it better” mentality pervades the entire APR staff. Every one is an enthusiast, and you get the feeling that coming to work in the morning is a lot like going to play in your garage on the weekend. I visited them on Labor Day, and you wouldn’t have known it was a holiday, since the shop was busy prepping race cars for the season-ending Continental Tire Sports Car Challenge race. Keith Lucas, APR’s director of sales and marketing, and Arin Ahnell, APR’s marketing manager, both took time out to show me around the impressive facility.

One of APR’s hottest-selling products is its EMCS Program Switching tune, which allows VW, Audi and Porsche owners to select custom ECU maps based on available fuel grade. The stock ECU programming is also retained, allowing owners to easily switch back and forth between stock and tuned modes. The gains in performance are readily apparent, and there’s no better way to go faster for a reasonable amount of money.

In the case of my 2011 VW GTI, the stock car produces 216 horsepower and 227 ft-lb of torque on 93 octane gasoline. With just an APR Stage 1 tune, and no other mods, the car now makes 254 horsepower and 303 ft-lb of torque on 93 octane gas. Should I have to run 91 octane, I can easily switch maps and the car will still produce 250 horsepower and 294 ft-lb of torque. For track use, if I’m willing to completely drain my gas tank and run 100 octane fuel, my car will make 273 horsepower and 337 ft-lb of torque.

Numbers on paper are only part of the equation, and they don’t mean much if the car loses drivability in the process. That’s simply not the case with my GTI, which now pulls noticeably harder from 2,500 rpm to redline. There’s still next to no torque steer, which makes the GTI easy to drive at speed. In short, APR has transformed the car into the GTI that VW should have built.

So why didn’t VW tune the American GTI for this much horsepower? It comes down to building a car for the worst case scenario. While the 2.0 TSI is a fairly robust engine, if an owner opted to use 89 octane gas (instead of the required premium) and then flog the car in 110 degree heat, bad things would happen. It’s cheaper for a manufacturer to limit performance than it is for them to replace engines in cars that aren’t properly maintained, or that are driven without regard to temperature and conditions.

If you’re a VW or Audi fan, chances are you already know about APR. If you’re new to either brand, bookmark GoAPR.com, since you’ll probably be buying stuff from them in the near future.