A change in sound when accelerating led me on a search to find out what was going on. Snooping around beneath the S4 revealed this:
Apikol B5 S4 Rear Differential Mount
Found it! Fortunately Apikol sells just the bushings for the mount so I ordered a pair to replace the failed parts.
Apikol Differential Mount Bushing
It turns out that there are two versions of this bushing so I needed to order both since I did not know at the time which version I have. I’ve documented the part number in case this happens again.
Starting on New Years Day I am taking advantage of some extra free time to get ready to swap the Frankenturbo F21s into the S4.
FrankenTurbo F21 version 3S4 Engine Pull Preparation
The S4 sits on a set of dollies so it can move about the garage easily for positioning. The car is at an angle in the garage when the engine hoist removes the engine.
S4 Engine Pull Preparations
Spending Friday evening removing the engine.
S4 engine out
Saturday is turbo swap day. This took a bit longer than usual on account of the Mamba wastegate bracket on the passenger side being too big.
Mamba Wastegate Bracket
Some cutting and filing of the bracket is done so that it will fit in place because the unmodified bracket contacts the cylinder head and/or starter.
Mamba Wastegate Bracket Modified
On go the new F21s.
Frankenturbo F21v3 Driver SideFrankenturbo F21v3 Passenger Side
Before installing the engine the wastegate preload is set to 12 psi. The setup is using the Yellow springs from the Mamba collection of springs.
I never got to the wheel bearings as the driver side rear axle bolt proved to be very stuck and I concluded that a shop with an impact wrench would be the most likely place to get it removed.
Silver B5 S4 Stuck Axle Bolt
Tuning was on the third revision, with the remainder to be carried out by the S4s owner when it was driven away.
B5 S4 Engine
In the meantime a backlog of turbochargers has grown in the corner of my garage.
BorgWarner RS6 – FrankenTurbo F21 – TiAL 605
Between the turbochargers and completing this engine build,
Engine Cleanup
and trying out the Mamba Wastegates, I have a number of options for future projects to tackle.