Originally Posted by AW8

Although there definitely weren't any official Alpina X5 E53's it's perhaps ironic that many claim the 4.6is & 4.8is engines were developed by Alpina. The 4.6is having identical 347 BHP output to the engine in the Alpina 5 Series E39 B10 V8, however I note the 4.8is produces 360BHp and the later E39 Alpina B10 V8S is quoted as 375 HP which seems to be a discrepancy, I read the difference between 4.6is and 4.8is engines is that the later car has a longer stroke so perhaps the e 4.8is is an evloution/development of the 4.6is engine as opposed to a copy of the E39 V8S lump,(guessing the 4.8is mpg gain might be perhaps due to ECU Map/6 speed box/Xdrive ???), It has been stated that Alpina B10 engines were handbuilt but the the 4.6is engine was a blueprint of the Alpina B10 V8 unit but made by BMW, (rumour states BMW had allegedly asked Alpina to build the 4.6is engines but Alpina couldn't meeet demand & so sold the blueprint to BMW). Other content online simply vaguely refers to Alpina having helped to develop the 4.6is and 4.8is engines.

I must stress I cannot testify the entire accuracy of this info as based on reading various 3rd party posts/articles.

No doubt this is not new info to those in the know, however, it may be of interest to someone.

I would welcome seeing a definitive authoratitive article on this writen by someone who was or is involved with BMW &/or Alpina.