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I'm wondering if direct injection hasn't been used on the Toyota atkinson engines for a reason. They've been using direct injection on the Yaris since before the 3rd gen Prius came out. My theory on this is that the port injection allows more time for the fuel to vaporize and the benefits of that outweigh the benefits and costs of direct injection. Due to the way Toyota does their atkinson cycle, part of the intake charge is pumped back out of the intake valve during the compression stroke. This allows more time for the fuel to vaporize and to cool the intake charge thus producing an anti-knock benefit. If they went to direct injection, they would loose some of this effect. Anyway, thats just my theory on it.
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