A plug-in hybrid retrofit kit for any car to increase gas mileage anywhere from 50 to 100 percent is coming closer with ongoing research, U.S. scientists say. Work at Middle Tennessee State University since 2008 has culminated in a 1994 Honda station wagon being retrofitted with a laboratory prototype of the plug-in hybrid capability, a university release reported Monday. Project leader Charles Perry, a professor of engineering, said the Honda has been fitted with electric motors in each rear wheel and a large lithium ion battery is mounted in the rear of the vehicle. Switching on power to the electric motors on the two rear wheels made a huge difference by reducing the amount of power required from the internal-combustion engine, Perry said. \"The whole point was to demonstrate the feasibility of adding the electrical motor to the rear wheel of the car without changing the brakes, bearings, suspension -- anything mechanical,\" Perry said. Perry said he is in discussion with several companies that operate fleets of vehicles to solicit funds to build and demonstrate a manufacturing version of the plug-in hybrid technology. Nine students who worked on the project, who now have graduated with bachelor\'s or master\'s degrees, came from the university\'s engineering-technology department. \"The wheel-hub motor is an answer to a problem,\" Brent Brubaker, one of the student researchers, said. \"It\'s innovative technology. You can take and bolt it on a car. When people see that, their eyes light up. They think it might cost a lot of money and are surprised when you tell them it might be $3,000.\"