[bestclimb]

I think 5.

the flywheel stores rotational energy from the power stroke to drive the engine through intake, compression and exhaust.

A power stroke lasts 180 degrees (actually less as torque comes to 0 on the top and bottom of the stroke) in a zero inertia engine, or if the load (work being done and internal friction) exceeded inertia the engine could stop. torque reaches zero at the bottom of the stroke, and rings and bearings and pumping losses continue.

A 4 cylinder 4 stroke engine must go through 720 degrees for each cylinder to fire. so in 2 revolutions each jug fires once. with 0 overlap which means one fire is going out, just before the next starts.

with 5 cylinders there is some 36 degrees of overlap as one cylinder is about 18 degrees from ending the next one is already 18 degrees into it's power stroke.

with 5 cylinders there is 900 degrees of power stroke by the time all of them fire. As 360 does not go into 900 nicely there is some overlap.

It would not be a smooth running engine as the power pulses would not be smoothed by the flywheel.

as for starting, one could rotate the engine to just after TDC then fire a spark off.