The H1 returns this year as the H1 Alpha. It is 2 inches taller and seats four passengers in its massive body. It is available as a four-door hardtop or an open-top model. Its new powerplant is a 300 hp 6.6-liter turbo-diesel V-8 engine with aluminum cylinder heads and direct fuel injection. A new five-speed automatic transmission also comes standard. The H1 is of course full-time all-wheel drive. For 2006, the HUMMER H1 receives a new engine and transmission. It also has minor design changes.