Originally Posted by 1ViciousGSX

Well it should have been close enough to check the mileage with. Lets face it, we don't always know we get what's advertised on the pump anyway, due to variables at the plant. But what would be the worst case, .5 Octane? If so, that shouldn't be a huge difference.

Originally Posted by Johnny Langton

The chemistry involved with octane additives and base fuel supplements to make base fuel stock either 87,89,or 93 octane is a complex process.
What you're considering "close enough", could very well be far less than what you think due to the chemistry of the additives mixing in your "blend".
JL

Originally Posted by 1ViciousGSX

Got a chance to do a tune comparison. And got some surprising results.
Drove from Huntsville, AL to Baton Rouge, LA and back for Thanksgiving.

Base info:
Truck specifics in my sig.
No trailer, only the truck.
All tires pressures set to 60 psi cold.
AIT stayed in the 30-50 deg range.
Coolant temp 190-194 deg.
Engine load 15-65% depending on the overpasses I encountered.
Mobil1 5W30.
Cruise control set at 75 mph (by my GPS, speedo said 77) for a real world test, never touched the brake or accelerator unless needed due to traffic. I would say 95+% of my drive was just allowing the cruise control to do it's thing, good or bad.
Filled up each time at an off ramp Chevron station, so no in town driving what so ever was involved.

5-Star 93 Octane Perf tune w/93 Oct
383.90 miles driven
28.02 Gallons used
13.70 mpg

5-Star 91 Octane EconoPerf w/89-93 Oct blend (sorry, we don't have 91 here)
220.00 Miles driven
17.17 Gallons used
12.80 mpg

Surprising to me that the Perf tune got 7% better mileage than the EconoPerf tune did. But that might be due to higher ignition timing in the 93 Perf tune.

The difference in price between the two octane fuels was $.14 which is roughly 5% more in cost between Plus and Super grade. So by my math (which isn't always the greatest), the better mileage off-sets the higher cost of premium fuel by a positive 2%. This confirms what I thought would happen when the engine is allowed to work with higher octane fuels and tuning that takes advantage of it. I wonder if that benefit would be even higher going from 87 to 93 Octane?

So are you really saving any money by using the cheapest grade fuel? From what I got here, it could be costing you more. But keep in mind that you need a tuner to get the benefits. Seems to be worth it to me.

Any thoughts and comment are welcome.

Originally Posted by bill11012

What were you seeing for MPGs stock?