Well... if you build a bike around a complete flat four diesel, you will never want for power.
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I don't recall any... *good*... automotive diesels in the sub-liter range... Piaggio has a 400cc, but that's torpid... makes about as much power as a 125cc gas motor. Tata has a 700cc making... wow... 16 hp. That'll probably get you to 140 km/h with a good tailwind.
Even if you do cut down a decent automotive diesel, I don't expect the turbocharger system would work properly with the lower displacement. I think your aim should be to keep the whole thing... Hyundai has a 1.1 with about 75 hp, which should be enough for a motorcycle to do what you want it to do. And it should be small enough to fit a motorbike frame, as well.