A very simplified approximation of product gap can be calculated if you assume infinite product acceleration from one conveyor to the other. If you are interested, I will help you find the solution, but I can't just give it to you.
Vx = upstream conveyor speed (m/min)
Vy = downstream conveyor speed (m/min)
L = product length (m)
G = gap between products (m)
Note that the units of the conveyor speed must be the same, and the gap units will be the same as those for the product length. Please use lower case "m" for metre.
If we assume that the product will accelerate from speed Vx to speed Vy at the instant that the leading edge of the product contacts conveyor y, and both products start fully on conveyor x, how much time will pass before the leading edge of the trailing product will contact conveyor y?