I'll ad that Any gas car that is turbo-ed, and is computer controlled, will ad extra fuel to keep the car from leaning out and blowing.
With diesels, you need to add boost according to your fuel input, and gas cars add fuel according to their boost. They seem to work on different concepts.
I've seen examples of turbo diesels consistently getting better mileage then N/A diesels. My mechanic dropped a 1.9L TDi from a 2001 golf into his 1990 jetta, added bigger injectors, a bigger turbo, and turned up the fuel pump. The car spews black smoke all over the place, is it pretty fast for a diesel, but he can still get over 50 mpgs on a car cruise that included a few little races on the highway with turbo-ed gas cars and vr6's (tdi won), and Got waaay better mileage then I did with my stock 2005 tdi-pd, driving normally.
My friend has a tdi beetle. He was happy with his mileage but decided to chip the car, and add bigger injectors to get better performance out of it. He doesn't care about mileage. However, By upping the boost and injectors, he now gets way better mileage, and a much faster car. The same guy also put a Tdi in a corrado and modified it for performance and power. He ended up with a car that can get over 700km to half a tank from normal to slightly aggressive driving.
Gas cars sorta get a lot worse mileage as you mod them for power. diesels, in the experience of seeing my friends mod their cars, get better.
