Just give them an engine displacement and so much fuel per kilometer. Let them figure out the rest on their own. I would rather like to see different engine layouts from different manufactures. I never figured out why the FIA said everyone had to run v-10's. They didn't make that rule until after the last mfg., Ferrari, finally made the switch anyway. If VW wants a Renault want a 4 cyl & VW want a W-12, let them.
Even Indycar lets you change the mapping during the race. If you are running out of gas, you have to back it down, or gamble with not finishing.
I always found it exciting when someone ran out of fuel with just laps to go. You no longer have cars breaking down with regularity to keep even that last bit of anticipation.
The FIA locked down to V10s when Toyota came into F1 and said they were building a V12 instead. This caused havoc in the background since Toyota showed up with a blank check. Toyota was about to buy a championship, or at least try. The FIA locked down to V10's so no other manufacturer already in F1 with a V10 would spend even more R&D simply to test a V12 engine.