As some know I have found and run a 4S pack in my XS (both of them).
Here's the video of 4S in my XS SS
When you run 4S, don't attempt backflips. lol This is a Wheely king axle from my RTR.
After over a year of abuse on 3S in the RTR I upgraded to CVDs. I bought the Hot Racing CVDs because they said 2mm pins in the description. This is FALSE. The Hot Racing CVDs use the same 1.7mm pins as stock XS. I only installed the front set at this time. I run the HPI CVDs in the XS SS and haven't broken the pins yet, but 4S is sure to be their downfall.
Another axle bit the dust, this was from a RS4.
Diff gears and bearing.