Both are 4.4-litre twin-turbo V8s with the turbos in the valley. The S63 is the engine in the M5, M6, X5 M and X6 M. The N63 is the engine in the 550i, 750i and X5 50i. Listings mix them because the displacement matches. The cranks, the turbos and the maps do not.
Same size, different engine
An F10 M5 uses an S63B44. An F10 550i uses an N63. Putting the 550i engine into the M5 is not a cheaper rebuild. The gearbox, the sump, the cooling and the computer will not accept it as the original engine. Order the S63 for the M car and the N63 for the 50i or 550i.
What to ask on an S63
Ask the full code, S63B44A or a later S63B44B or T4, because the turbos and the power are not the same across M5 generations. Look at the valley for baked oil and at the charge pipes for cracks. These engines are heavy on a pallet, around the upper end of what a standard tail-lift likes. Confirm the workshop has a way to lift it before the truck arrives.
Rod-bearing service is a fair question on a used S63 that has been driven hard. If there is no history, plan to inspect the bearings with the sump down rather than hoping the listing's mileage tells the truth.
Do not downgrade to an N63
If the S63 is more than the car is worth, the honest answer is sometimes a different car, not a 550i engine in an M5 shell. We will say when we do not have the S63 code you need. We will not substitute an N63 and leave you to find out at coding time.
S63 guide · N63 hot-V checks · S63B44A from an X6 M
Lift and fluids
Confirm the workshop lift and the stand before the truck is booked. An S63 on a pallet is not a two-person lift. Fill the cooling system with a vacuum tool, use the oil grade for that S63 code, and check the level again after the first heat cycle.
If the car is an M5 or an X5 M, the gearbox oil and the transfer case are separate from this engine. A noise after the swap is not automatically the engine you just paid for. Agree who is diagnosing what before the car leaves.
The yard is at Andreas Meyer Straße 38, 22113 Hamburg. Call or WhatsApp +49 15510 030835, or email autowerkeengines@gmail.com, Monday to Friday, 9:00 to 16:00 CET. Shipping is 249 € per order. We are an independent seller, not BMW AG.