[sheepdog 44]

The only way you're going to get 200mpg or more is by severe electrification. You can get 120 mpg with complete aeromodding and hypermiling technique below the speed limit. Swapping the engine for a 600-800cc japanese microcar engine with leanburn will net you more. However the engine wont be happy with the cars weight even at 1,800lbs! You'll have a city car then unless you can shed 500 or more lbs from the car. With the Insight there isn't really much room to shed weight unless you completely stripped the car to it's frame, used plastic for all the windows and body panels. You could reconstruct the frame as a single seater and turn it into a three wheeled tadpole car running off a motorcycle engine.

The above seems rightly a time and labor intensive approach to go if you want hyperefficiency, and extremely low operating costs. What i suggest is you save all your time and money and just convert it to electricity. With the most efficient production car platform ever made as a basis for conversion, you'll get more power and much better wh/mi efficiency and range, all at a far less cost cause you'll obtain more usefullness of the smaller battery needed to accomplish it.

With a full boattail, front end, side skirts etc, you can get the CD to .17 or better. and you'll get 33% better performance or so than any production EV. Including the EV1, which never had the pleasure of running on lithium!

Or you could go halfway and just make it a plugin hybrid by leaving the engine in. Say 40 mile electric range on a 10kwh battery +-2.5kwh, and then 75mpg average on gas! What a joke the leaf and prius would look like! At that efficiency you'll be averaging far better than the cost equivalent of whatever a 200mpg car would cost to run on gas. And you could build the thing for less than half what it costs to buy a Volt or Prius plugin brand new.

You will have to beef up the suspension though for battery weight. I think the total weight of the car would be 2,000-2,400lbs depending on the components used. Thats still pretty good compared most cars.

The main reason I suggest electrification (along with aeromodding) Is because it requires less time and labor as opposed to severely altering the structural body of the insight to obtain 200mpg on gas. Also 200mpg on gas is unrealistic and comes at too high a sacrifice, unless you alter the (very poor) hybrid component of the vehicle. The only thing that comes close to 200mpg at 55mph on gas is a streamliner 125cc scooter.