Gotta agree with lkchris a bit. I think the M103 is a great engine, but I'm much more fond of some BMW engines. I personally really like the M50/52 engines. Long lasting and a decent amount of power and really smooth, and sounds great to boot. The power delivery is very linear and predictable, and just a blast to drive. I'm also driving an N54 motor in a newer E90 BMW and while the power is awesome, I'm just not confident that the engine and turbos will last like the E36/M52 combos have done so in the past. Time will tell...