Yep, the kp31.. That thing is no larger than my fist. I mean, you can barely stick your finger in the comp inlet!!! no wonders why this engine makes around 70 hp boosted!!!

another cute little turbo is the new gt 1241.
here, i took a picture of them with a lighter to show how ridiculously small they are. (i swear, that lighter is used only for size comparisons!!! nothing else!! )

 

That lighter has resin on it

 

I saw a smart car turbo on ebay, although it was (and I think they all are) integrated with the manifold, meaning you'd have to cut it off & weld on your own flange.

 

could a 125cc engine spool any of theses.