The 4.8 will fit. However, there will be differences that you would need to address that will be additional cost over and above the 4.4 replacement.

I would stay with the 4.4 engine. The 4.4 will be more plentiful and you would be more apt to find a good one with less miles. There are mods that will increase the performance of the 4.4 to that or greater than a stock 4.8. It is possible that a 4.4 with mods would still be less than a stock 4.8 total cost of replacement.

Most engines will come with a warranty of some sort. if you mod either engine I suspect the warranty will be voided.

Unless your exiting engine can't be rebuilt, I would get an estimate to repair the 4.4 engine you have. Rebuilding your existing engine, with at a minimum used parts, should be the least expensive overall option.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas