Engine Switch Out ‘73 CSI

[Whipcity]

Am considering another engine switchover on my ‘73 E9. It presently has a “tired” 635csi power plant. Don’t have full provenance so cannot say for certain how many miles are on it. My BMW guru suggested “shoe horning” in a 3.5 from a M5, probably from the late ‘80’s. He contends better idle, broader power curve, 4 valve technology, etc. Has anyone actually done this to their E9? Would welcome input and suggested mods that would seem pertinent.

 

[sfdon]

Sounds fun- did your guru give you an estimate? Has he done the job before?

 

[Whipcity]

Yes he did, depending on condition of “new engine”. Yes, he’s done it many times with different makes, but not in this instance. I was hoping that BMWNA might offer factory rebuilds like what I got for my tii. Makes a world of difference/piece of mind coupled with a short term warranty. The ”guru” is an independent BMW/Porsche/Mercedes-Benz repair facility literally next door to my man-cave, yeah I’m spoiled. He’s only limited by the amount of diagnostic equipment/tools needed in newer gen Bimmers. He’s even offered to purchase my pair of Bimmers when I can’t drive a stick any longer. He guessed the bill would be between $10-15K. Thanks for replying to my thread!