Why no direct injection?

Prius is not a slow car. It's the drivers that are slow. I bet people who ask for that extra power are not even using 50% of the existing power.

 

DI only really affects performance and emissions. You don't magically gain an improvement in MPG, you get it through VVT which many manufacturers implement together. Any improvements to fuel economy would be because of the perceived improvements in performance and not needing to press on the accelerator as much or at low loads (idle) that don't really apply to the Prius. Remember VVT reduces pumping losses, DI allows higher compression ratios and better fuel mixture, it wont magically reduce the amount of gas needed for ignition or reduce the amount of unburned fuel except in meaningless quantities over a tank of gas in the case of a Prius.

tldr; DI adds a premium to the cost of the vehicle that would only apply to higher end vehicle like a Lexus and not to a vehicle like the Prius which is designed for price/fuel economy over power.

 

The Hyundai Elantra and Sonata both have Direct Injection and cost less than a Prius. The Elantra can easily give well over 40 mpg calculated over many tanks fills crossing the country. I did that back when I was trying to decide which car to buy a Prius or an Elantra. Well documented on this forum
I think a Prius motor could benefit with direct injection and not cost too much.

Mike