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2013 Dinan S3 BMW 550i

Steve Dinan has been enhancing BMW models since 1979. But don't throw his company into the ring with the dozen or so other tuners who tweak, tinker and piggyback upgrades on the famed German marque. Dinan is a tuner, but it's also an engineering firm that writes its own software, builds its own parts and then backs everything it does with a factory-grade warranty. That sort of fastidiousness comes at a