I came across the following interesting video: Capacitor to start engine. Perhaps it is most interesting for track use since it looses power relarively fast. Harald
The real future for capacitors may be to store power for a "road KERS" system. They hold a lot of power and can release it fast, but leak power over time.
Peter, 66, 2016 Porsche Boxster S No longer driving Tarka, the 2014 Plus 8...
There is a certain functional equivalency between capacitors and batteries. Price and latency of charge determine which to use and that, almost always, dictates a battery. Weight is seldom an issue for automobiles.