The wiki on oil cracking ratios

[AnonymousCaribou]

https://wiki.factorio.com/Oil_processin ... processing

Under Advanced Oil Processing, it says the optimal ratio is 5:1:7. That means:

5 Refineries turn crude into 5 Heavy Oil, 22.5 Light Oil every 5 seconds
1 plant on Heavy Oil Cracking turns 4 Heavy Oil into 3 Light Oil every 5 seconds

...so in a 5 second period we're making 5 heavy and using 4, so we'll build up a surplus and the refineries will jam, right?
Anyway, on the light oil side we now have 25.5 light oil every 5 seconds (22.5+3)

7 plants on Light Oil Cracking turns 21 Light Oil into petroleum gas every 5 seconds

so again we have 4.5 extra light oil which means it will eventually jam.

If my understanding of how things work is correct then the ratio should be 4/1/7 - produce 4 heavy oil and it gets completely used by the 1 heavy cracker, then 4*4.5+3=21 light oil which the 7 plants can handle exactly.

Am I misunderstanding something here? Is there some reason we'd want exactly that amount of extra resources for some other crafting task, or something?

[Mehve]

The time given for the processes are a base time, which is further modified by the building itself. Refineries have a base speed of 1, which means no modifying of the process time, but chemical plants have a base speed of 1.25, which means they operate at a slightly faster speed. With that taken into account, the "perfect ratio" works fine.

[AnonymousCaribou]

That makes sense - thanks!