Quote Originally Posted by RS View Post
Does the engine have to be closely based on a road car engine fitted to that model or can the cylinder capacity be enlarged? If no such changes are allowed then it seems rather short sighted they didn’t do something with the restrictor size. It could be rather limiting if a manufacturer does not have a 1.5/1.6 litre engine fitted to the road going model.
That's a good question. In Rally4/5 they're based on the road car engine and once MSport is apparently using the Fiesta ST 1.5 engine (instead of a 1.6) on its Rally3 car, probably they must still be based in stock engines (it's becoming hard to remember that they were meant to be just a 4wd Rally4 upgrade...).

Btw, another strange reg move is to have all Rally4 cars with the same weight (and restrictor), meaning that 1.0 cars crews will hardly be able to match 1.2 or 1.3 rivals, as they now do. And once Rally5 cars won’t get the 30mm restrictor, probably we’ll end seeing the fastest Rally5 drivers pretty close to Rally4 competitors. Time will tell.