At least in the B-Cycle EA888, there were significant changes. Not sure about the GTI/GLI though.....
www.mechanic.com.au
From article in link above....
Other improvements
Most of the other refinements to the Budack Cycle engine were made with the aim of reducing weight and friction, which when taken together, make a significant contribution to the overall efficiency of this engine. Briefly, these improvements include the following-
- Improved engine management system that uses four microcontrollers to control valve lift and duration, which has the effect of producing seamless transitions between Budack -, and Otto Cycle engine operation
- Redesigned piston rings to improve gas sealing and reduce friction
- A down-sized turbo charger that requires a lower drive pressure, thus reducing turbo lag
- Redesigned intake ports to improve gas flow
- Narrower balancing shaft drive chain to reduce weight
- Reduced main bearing journal diameters on the crankshaft to reduce both friction and weight. While the weight saving is significant, reducing the journal diameter from 52 mm to 48 mm to reduce friction was made possible as the result of this engine’s lower brake mean effective pressure at high, or maximum engine loads as compared to a conventional AE888 engine
But i don't know if any of this limits the application to strictly XW20 where reliability is concerned.