The Volkswagen Group has long positioned its TDI offerings as fuel-efficient alternatives to conventional or even hybridized powertrains, but the company also has a reputation for churning out go-fast diesels, too—look no further than the Touareg V-10 TDI, the Euro-only Audi Q7 V-12 TDI, and the GTD. And the number of sporty compression-ignition models is [...]