Just curious if anyone has checked this. I've never run anything but premium and was wondering if the factory got there numbers with 87?

 

isn't the HP rating like 402 on the regular octane and 412 on the 91 or 93 ? i thought i saw that someplace in the Ford Lit. But i have been wrong once or twice before so maybe not
yup here it is from there (Ford's) spec sheet
"Horsepower (SAE net @ rpm) 305 @6,500 Regular Fuel: 402 @ 6.500, Premium Fuel: 412 @ 6,500"
but after some thought i bet you are asking for "real world" numbers and i hope someone has them too would be fun to compare !

 

412 rating is on 91 Octane.

You lose about 10 hp using 87 octane.
You gain essentially no power using 93 Octane instead of 91 octane in a stock car. I dynoed tested it. The stock ecu is programmed to make it's peak power on 91 octane, adding anything higher seems a pure waste of money. I may try going straight 100 octane and dyno it and see if even that adds any power to the stock tune, but I doubt it highly.

If 402 or so hp is plenty for you, use 87.
But if you want the full 412 (really it's about 416-418) the factory rates the car at, use 91. If you are in a state that offers only 93 octane, use it, or mix it up. Use 93 sometimes and 89 others and you'll have a nice 91 octane mix for full stock power.