Originally Posted by JohnM.

For overall simplicity, high number of production years (easy to find good used parts for cheap), the M103 wins hands down. The M104 is more refined, but has more expensive issues (wiring harness), in addition to the head gasket issues with both engines. The M104 feels a lot faster, but in reality, I think it's within .2-.5 second 0-60 difference between the M104 and M103. M104 feels faster due to torque down low that the M103 lacks. Otherwise the M103 seems to rev more freely. The 94/95 HFM cars were also heavier than the M103 cars, so that negated a good portion of the extra power.

Also, nothing can beat the sound of a redlining M103, I'm sorry. The M104 is too quiet and modern sounding compared to the "screaming" M103 for my tastes. Tunnel blasts are waaaay too much fun in a otherwise stock drivetrain/exhaust 300E.