[Daox]

I'm going to have to agree with James. It is going to be nearly impossible to beat the 1.0L lean burn engine that is currently in the Insight. To top it off, the Insight has just about every easy ecomod that you can do engine wise (and otherwise for that matter). Just to name a few, the gearing is already tall, it has lean burn, the engine is small, and its got regenerative braking. You basically want to throw that all away and start from scratch?

Guys that are hypermiling these cars heavily are already getting 110+mpg in the summer in nearly stock form. I think one of the best ways to get a little more mileage out of these cars is to start manipulating the hybrid system, basically what mima can do for you. Also, use a warm air intake on it to extend lean burn capability. I really don't think replacing the engine is the way to go. Other mods can certainly bump up the mileage, but Honda has already done a great job at optimizing the whole hybrid drivetrain.