Can someone explain the rational behind the firing order used in the 4 cyl Lycomings? Seems that 1-3-2-4 would not be the smoothest sequence but I'm sure it is.
That's the same order as a Subaru, so it's not without reason. Best balance is achieved with the boxer design (eg opposing pistons reach TDC at same time), but that means the firing order must be the way it is. It does however make them sound nice, even if the 6 is smoother with it's overlapping power pulses... Note that you could have a different firing order with a "180 degree V-4", but it would be extremely unbalanced.
Note that you could have a different firing order with a "180 degree V-4", but it would be extremely unbalanced.