[elhigh]

Get a good Lombardini diesel and drop that in. That would be easiest. You would just have to come up with an adapter to attach the engine to the existing transmission, but lots of people have done stuff like that already.

I like the idea of adding hybrid capability to the car but for the shadetree mechanic it would be really difficult - you would need to create and install a completely new drivetrain, either to replace your existing one or else to replace your undriven axle. The latter would actually be easier, I think. But going this route would add a lot of weight to a car that doesn't have a lot of capacity in the first place.

Another concept would be a series hybrid. This would also completely replace your existing drivetrain. An electric motor would become your prime mover. You would have batteries to provide surge power when needed, but there would also be an engine powering a generator. Ideally the engine would be just powerful enough to provide slightly more power than the vehicle needed at a steady cruising speed, which gives the designer the opportunity to install a smaller engine and run it closer to its most efficient speed. The slightly excess capacity and regeneration would provide the extra power needed (stored in the small battery pack) for acceleration, hills etc.

Not many go this route. I first read about it in Mother Earth News in the 70s; Mother then tried it on their own a couple of years later and reported that it did okay. But it's a squeeze getting all that non-optimized hardware under the hood.

Hmm. I wonder what the dimensions of the Prius C's drivetrain are, and how well you could fit something like that under the hood of your battered old 4. That would buy you all manner of hybrid capability, ready-made.