there was a couple of years ago, a US based project; that you convert say your car into a Hybrid instead.
It was basically a 'fit 2 washing motors' system.
For a FWD car, you would be placing these hub style motors to the rear wheels only.
A tight fit between the wheel and it's hub
All powered only while the IC was turning and burning
Can see many downfalls, if one considers someone trying to further retrofit this concept to run on battery alone - considering Auto trans damage if running off batts whilst the IC Off
I had an idea years ago to place a DC motor/generator inline with the driveshaft of a rear wheel drive vehicle to produce a DiY hybrid from an ordinary I/C vehicle. Of course, batteries would have to be installed somewhere and powering the driveshaft motor would have to be sync'd with the I/C engine, etc. Placing the motor/generator where it would clear the car's chassis/frame is ONLY ONE of the problems with this concept. For front wheel drive vehicles ... hmmmm, let me think. Maybe someone out there has already implemented this idea.
It would be conceptually like the nowadays electrically-assisted bicycles that maintain the original gearing by installing a hub motor/generator (motor/gen for regenerative braking) and a battery and controller. It's a very common setup and kits are sold to electrify a pedal bicycle, yet maintain the ability to pedal with the bike's original gears. In fact one are two of these electrified bicycles are for sale on craigslist/thailand.