Around Memphis, all gas stations with 93 octane juice is blended with a "minimum" of 10% ethanol. However, one station near my house sells 91 octane pure, 100 % gasoline. Pump is differentiated by neat blue handle.

Having said that, which is better, 93 with at least 10% blended ethanol, or 91 octane pure gas?

My gut tells me 91 pure is better as I suppose the ethanol dilutes the energy density of gasoline. I'm not a scientist, just guessing.

Anybody have a better, scientific answer?

 

Nothing scientific, but my gut tells me modern cars are made to burn "some" ethanol without causing whatever harm older cars might have suffered from.

The gas lid calls for 93, and that's what I've burned for the past 10,000 kms.

 

We have read reports of 100 octane benefits but I am not certain whether a 2 octane difference with/without ethanol is noticeable. As an oxygenate, ethanol does dilute the energy concentration but it introduces more oxygen for a cleaner burn. This may prolong the life of or improve the efficacy of your catalytic converters.

My guess is you are attempting to determine which is better for performance since either is perfectly fine for your engine.
The scientific method suggests you try each fuel at your local drag strip under the same conditions. Go in the name of science!

BTW I am a petroleum engineer and not a chemist

 

See if this will help you in your quest for pure gas: http://pure-gas.org/

 

The car was designed to run on oxygenated fuel with up to 15% ethanol. The injectors can deliver enough fuel to compensate for the difference in energy density. The extra octane will only help regardless of the presence of ethanol. Best to go with the 93 octane.

Cheers,
- Patrick

 

This is a site I use. But you have to call station and see what Octane they sell.
http://www.racegas.com/fuelfinder

 

Ethanol gas blend will burn somewhat cleaner on the DFI engines.
In Canada where I live, the car starts better on cold days with the ethanol blend. The car likely gets a bit better mileage as well.
We have option of 94 octane "gas" which the car runs really well on the track. Porsche Canada also gives buyers a discount card for this fuel. I alternate 94 ethanal blend with 94 Sunoco/Petro Canada gas & the car runs well on both.
If you're just driving around the city & don't get the car out for regular drives > 50 miles you might consider a gas with detergent like Shell to prevent residue build up on the DFI engine.

 

Generally the engine is better off with the proper octane grade of fuel. With this the DME can dial in more ignition advance and this results in more energy from the burning of the fuel being converted into mechanical energy.

Based on my experience with my Turbo with 93 octane (vs. the 91 it is forced to live on here in CA) the engine is more responsive running 93 octane gasoline. I wish I could get 93 here in CA.

However, there could be a case in which the engine just doesn't like the 93 octane fuel. I doubt this will prove to be the case but Porsche advises that if the engine acts up, reacts poorly to a gasoline, to try a different brand of gasoline.

Generally the engine will get less milage with ethanol treated gasoline. Ethanol contains less energy than gasoline. Additionally the ideal air/fuel ratio of air and ethanol is richer (approx. 9:1 vs 13:1 for air/gasoline) so it takes more ethanol to arrive at a proper mixture.

Try 93 octane gasoline. IF the engine is ok with it continue to use it. If the engine manifests any odd behavior, hard to start, mild hesitation, that sort of thing, switch to another brand of gasoline. Ideally it should also be a 93 octane fuel but if there are none around then try a 91 octane fuel.

Be sure whatever gasoline you use you buy from a busy station to ensure you get the freshest gasoline. Premium gasoline goes staler quicker than the lower octane grades of gasoline and stale gasoline can lead you to believe the engine doesn't like the gasoline when in fact it is the staleness that is at the root cause of the engine's reaction to the gasoline.

 

This is the truth.

 

I have a GIAC Stage 2 tune. It is programmable for 93 and 100 Octane tunes. They clam the 100 oct tune adds about 40 WHP. No Dyno numbers as of yet.
But I can confirm easy 40 WHP.
I am hoping they lower the $9.00/ gal price soon. It getting expensive!

 

Macster good summary. Sunol carries high octanes at the pump but I'm sure you're aware