Hey folks.
Came across this thread while checking to see if there had been developments on other projects I'm following and decided I'd throw my $0.02 in.
I have a project car (1965 Ford Falcon Wagon) that I'm seriously considering running with a cap bank instead of batteries primarily for space and draw constraint requirements; cap banks are nice because they can take a whole bunch of different/odd shapes. I'm building my existing cap bank into a triangular log shape and will be using that as a jump pack for my pop's racecar on track days (it doesn't have an alternator and our current battery charger takes a long time to top off the battery) as an example.
I'm currently using what amounts to a motorcycle battery in my 2009 Mazdaspeed 3; unfortunately, the Mazda draws about a quarter amp under full shutdown (measured through voltmeter), so a single 500 farad bank (6x3000 farad caps in series) won't cut it for my usage of the vehicle (sometimes 5+ days without driving it). As it is, if I don't drive the car for more than a week, it may not start as a result of the passive drain.
Here's the video of my slowly dying battery kicking over my Mazda on a cold start:
That said, I have done testing with capacitor banks, and they are viable if you daily drive the car and/or have a solar cell for trickle charging to counteract any low amount of drawdown and/or have an older vehicle which has very little key off draw, like in the following video.
Here's a vid of my bank starting an older V8:
NSFW language (I was excited)
https://vimeo.com/86949274
Also, if anyone is interested, I've included a screenshot of my capacitor math Google Sheet and I can provide any formulae requested.