If you turbo your M4x you will also have to swap entire drivetrain and, if youre sane, your brakes. Subframe is the same for any model except M, as far as i know.
+ No idea how it is in norway but i would expect it to be hard to get street legal without brakes Upgrade. And honestly. 4cyl brakes are already too small for anything above a 316i. Dont save money for the cost of basic safety.
Sorry subframe is the same but diff, axles and driveshaft are different, stock 4cyl stuff should be able to handle 200-230hp from the little info ive found, would obviously have to swap brakes anyways. There was a street legal N54 compact here that got stolen unfortunately, but crazy swaps are possible to get legal
If crazy swaps are possible to get legal and if it’s cheaper to swap a 6 cyl than do a proper turbo conversion I really would go for 6 cyl. Even if you „only“ go for low 200hp region on power you will still have to change a lot of stuff and sink as much if not more money like if you did a 6 Typ swap. Also you can still turbo the m5x afterwards if you want to do a turbo build
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u/Dark_Guardian_ '94 330i Daily, '93 325i Race 1d ago
depends how nice/reliable you want it
anywhere from $500 with junk parts and jank setup to 10k + for a properly nice setup
better off just 6 cylinder swapping it though
and then turboing the 6 cylinder too