Arrow

Why would Ford recommend 87 oct for stock, if you get better performance and gas mileage from a higher octane? The price is even higher, so it's more cash flow to OPEC all around.

Calculations and technical design aside, it's a performance car that the manuf. is recommending the lowest grade for the stock tune. Something has to be up with that. Doesn't make sense if it's bogus.

stratjakt

Was it a different brand or station of gas? The quality of gas and the mileage you get can vary pretty much from pump to pump. Brands with ethanol in the blend in particular get worse mileage, as it doesn't burn with as much power.

TheDutchTexan

High octane is refined better, less impurities, and it does boost mileage. Also, your car seems to run faster with it. Tune or no tune, it's the fuel that goes in mine. From the beginning we had it.

barge

Good enough proof for me, I'm going premium!

legendlime

Perhaps your regular fuel has more ethanol in the mix than the premium fuel,
OR the regular fuel you are using is very crappy, and the ECU is retarding the timing to compensate...(I am assuming Ford supplied this motor with knock sensors in this day and age...)
just my 2c...
CB