Should specific units/brands be added as a section of a related page, or get their own page?

For instance on Shifter would information about the Pingel Shift Kit be better as a subsection under "Electronic" or as a linked page. Or in Engine Control would talking about specific ECU brands be better as new sections or each their own pages (I can add info on at least a couple our team has tried)?

General rule of thumb is that shorter pages are better than longer ones. I'd recommend creating a unique page for the Pingel Shift Kit and linking it to the shifter page in a section called "Off the Shelf kits" or something. Same thing on ECU stuff, like I'd expect Megasquirt and Motec to have their own pages vs just being under "ECU".