I apologize sincerely if I’m wrong but what I see from F1 from on TV, there a spec series from what they say. Build your chassis to this spec and keep your engine to this hp. Sounds spec to me, they clearly don’t say it’s a spec series with there manufactures rules. I’m sorry this is coming from a fan.
I get what you are saying, they (FIA) come up with rules and everything is built within the rules. That’s not what happened with the TAG class, it was the opposite. The only thing that was similar with the TAG was all but one was a 125cc 2 cycle. The rules were made after the engines were built.
The TAG classes had engines with different bore and stroke, different ignition, different max rev’s, different type of carbs, different size of carbs, different type of exhaust.
With all these differences one engine would always have an advantage on a certain track. Nothing could be done easily that would work on all types of track. You had 10 pounds to the Rotax on one track it would get killed and on another track it would be the engine to have.
The point is, even back in the TAG glory days you had to have multiple types of engine if you ran the National scene. I know I remember one WKA race where a TAG driver showed up with three karts with three different engines on practice day.