4i, XR4x4, Capri, Granda there are turbo kits floating about for them all over the place. I had an XR4x4 2.8 turbo for a few years and I about to turbo convert my 4i.

The kits give big increases of power but you need to start digging deep if you want anything special and go beyond that. The most common thing to do is just whack a single turbo kit on a bog standard 2.8 which see's about 200bhp and a shedload of torque.

I have photos of the various single turbo parts here

As you'll see the single turbo uses a Garret T3.

A lot of people make the mistake of buying them and thinking they can get a lot more out of them like a cossie. But it gets expensive as the engines are real boat anchors.