Basically the same engine
Ignition is by a single coil and plug leads on the AUA and by individual coil packs on the BBY
Other than that the same
Latter BBY engines had better pistons to prevent piston slap developing around 2004 if memory serves
BBY is more prone to piston slap for some reason. I had a BBY engine in a previous 52 plate car, changed it for a Y plate with AUA engine (better specc’d car) but the difference in the engine noise and performance was noticeable, even though they’re basically the same engine.
Bluey, my AUA A2 is on around 138,000 miles and there’s no sign of any piston slap.
The previous BBY car sounded like a tank at 88,000 miles, and needed a refurbished cylinder head at around that mileage due to sticking valves.
The BBY had the better service history too….
Our BBY Piston Slap started around 60,000 Miles. Audi would have nothing to do with an “ Abnormal Warranty Claim “. It’s still going though at 130,000 Miles. Does not seem to be as noisy since I changed from Longlife 5w 30 to Millers Trident Fully Synthetic VW Specific 5w 40