Mustang maniac Jack Roush had done almost everything you can do with a car. He has raced and won, built and sold, crashed and repaired. So what's the next step? Jack Roush is going green.

Roush already has success selling alternative fuel vehicles to fleet markets. Now he's unveiling two propane-powered Roush Mustang drag cars. One is on display at the SEMA show in Las Vegas.

Clean burning propane is the third most popular fuel in the world and Roush has been converting vans and pickups to run on it since 2007.

Propane burns cleaner, lessens our reliance on foreign oil and 90 percent of what we use in the U.S. is from right under our feet.

For drag racing applications, propane has an advantage over gasoline because it has a 106 octane rating, compared with 93 octane for premium unleaded.

The first propane Roush Stage 3 Mustang will begin testing in mid-November in preparation for the National Mustang Racing Association season. The second, being built for Sarah Roush-McClenaghan, should debut in February.

Both 'Stangs will use the 5.4-liter V8 from the Ford GT, sans supercharger. The engine will be converted to run on propane. That means changing the compression ratio, porting the cylinder heads, adding a high-performance camshaft and valvetrain, and a wet sump oil system. These modifications should put horsepower numbers north of 600.

The SEMA car is on display at the Cruisin' Legends lot.