Feyhl had spent 12 years at AMG well before the tuning company became part of Mercedes-Benz in 1999, serving as that company's North American technical director and acting as a driving force behind the AMG Hammer—an iconic early 1990s automobile which was, for a time, the fastest production sedan on Earth, with a top speed approaching 300 km/h.
Over the years, Feyhl and company have developed high-performance products for virtually all Mercedes-Benz AMG vehicles (including the commercial Mercedes Sprinter van). While most famous for Feyhl's powerful engines, pizza-sized brake kits, and sporting suspension know-how, Renntech is in fact a full-line aftermarket supplier that offers everything from shift knobs and steering wheels to complete cars - most notable among these are the 200 mph Renntech E7.4RS (which was called fastest sedan in the world by Car and Driver in 1996) and the 2006 "Chrome SL" showcar—an SL-based project entirely covered in chrome. Each of these vehicles featured extreme performance, upgraded luxury features, and a fit and finish that met or beat the Mercedes factory cars.
Following the 1998 merger of Daimler-Benz and Chrysler Corp. (which became "DaimlerChrysler"), Renntech began expanding into the Chrysler category - beginning with the Chrysler Crossfire, a car based heavily on Mercedes-Benz SLK components (a logical move, as Chryslers began to utilize more Mercedes-Benz parts, more of Renntech's components became compatible).
More recently, however, Renntech has begun to offer products for other marques as well - specifically product for Porsche, Volkswagen, and Audi vehicles. These product offerings, while less exhaustive than Renntech's Mercedes offerings, focus on Renntech's core competencies: engine tuning, braking, and suspension, with an emphasis on the higher-end Audis and Porsche SUVs.
Historically, Renntech has been a prominent Mercedes-Benz specialist, and Feyhl himself is regarded by many as the USA's foremost authority on Mercedes tuning. Renntech's high-performance cars are often featured on the covers of major automotive magazines, including Car and Driver , eMercedesBenz , Motor Trend , AutoWeek , Modified Luxury & Exotics and others. In a feature article on Ray Durham's Renntech modified SL55, Modified Luxury & Exotics refers to Renntech as, "one of the foremost Mercedes-Benz tuners in the world.