The horse power you can get from a 2.5 ltr bimmer motor is limited and expensive. the hp gain you would get by changing the motor with a chevy or a bimmer v8 would be cheaper than if you were to turbo or whatever the 2.5farna said:Saw a 350 in a 500 series Beemer, but not the 300. A small Ford might be better, it's a couple inches narrower than the SBC. Better yet would be one of the small 60 degree V-6 engines -- 3.1L or 3.4L from a Camaro would be nice, or even a late model 2.8L. The 4.3L V-6 would have the same width problem as the SBC. Maybe a 4.0L Ford V-6? I'm not sure on width of it.
The big question is why are you switching? Just want more power, to do "something different", or the expense of rebuilding a Beemer engine? If the later the 3.xL V-6 might be a good compromise and still provide a little more power than the Beemer four.