A Sunoco station near me is going to be selling 91 octane non-ethanol fuel. Which would you prefer, 93 E10 or 91 non-ethanol?

 

91oct., no alcohol.

Straight gas has more energy than gas w/alcohol and the OEM tune is for 91.

 

You and your car won't notice any difference between those two; buy whichever is cheaper.

 

Ethanol Alcohol has 31.44 units of energy per liter.
Gasoline has 32.6 units of energy.

My ball point calcultor says the gasohol will be down 3.6% on energy compared to the pure gas.

Assume the 3.6% carries over to mileage and power;

26MPG becomes 25.06 MPG

Power becomes LS2=385.6HP and LS3 436 becomes 420.3HP

1 MPG isn't much but 14 to 16 HP is a big difference.

 

91.

 

You are correct on the mileage. It will be lower for the ethanol gas for the reason you state. But power will not be reduced. The engine computer will adjust to inject more fuel to maintain proper air/fuel ratio as judged by the O2 sensor. The higher rate of fuel injection is what causes mileage to drop, but it prevents power from dropping.

As far as the OP’s question, there are arguments on both sides, but none of them are compelling. It will just boil down to which issues strike your fancy the most. On the side of the 93 with ethanol, the higher octane would help Z06, ZR1, and modded engines, but not make much difference to others. Also a possible benefit to the 93, depending on which brand you choose, you can probably find top tier, while the 91 Sunoco is not. Don’t know what the price will be, but due to mileage loss with ethanol, the 91 ethanol-free can be up to 5% more expensive to be a breakeven for you economically. Some people rant and rave about the dangers and drawbacks of ethanol, but those are all very low probability risks. Those who shout the loudest about the risks are pretty much universally, the ultra strong political opponents of ethanol. And of course that brings us to the last difference, politics. Some feel very strongly about the politics of ethanol, with ethanol having both its strong supporters and strong opponents.

If it were me, I’d see the politics as a wash. Both sides have good points, but both sides are also guilty of exaggerations. I see top tier as valuable insurance against deposits, and my car is also one of the ones where the engine can make use of the added 2 octane. So I’d get the 93 with ethanol from a top tier brand.

 

Have you actually seen a top tier label or are you just going by the list of top tier fuel providers? I have never seen a label since I bought my 2013 ZR1, so I just use Shell because they're on the list in the owners manual. I asked a couple attendants/owner/operators early on, but just got blank stares.

 

Most stations don’t post it. The marketing types want things that differentiate them from others. So Shell advertises “nitrogen enriched”, Chevron trumpets Techron, and so forth. You might think they would want to post top tier to differentiate themselves from the cheaper gas, but the thing is, they don’t see cheaper gas as their direct competitors. They see the other big guys as their direct competitors, and almost all the big guys are top tier. Thus, they don’t bother to make a big splash about it. This is yet more evidence that the people who think top tier is a marketing conspiracy of the bad old oil companies are wrong. If it were a marketing ploy, then they would make a big splash about it. Right? So the fact that they don’t, says pretty conclusively that it is not a marketing ploy. It is just what they say it is, namely, a spec for better engine cleanliness that is set up by the auto companies to reduce auto warranty claims. It is a very real benefit, so I’d encourage you to keep buying top tier, even though you may have to go to the top tier web site to find out who the top tier companies are.

 

Every time I have seen the 100% gas in a separate pump and labeled as such, it has been substantially more expensive...much more than is reasonable.

 

The O2 sensor doesn't read energy of the fuel, it just adjusts the AMOUNT of air vs the AMOUNT of fuel by weight.

Alcohol has less energy per volume than gas so there will be less energy derived from an equal volume alcohol. Same volume of air, same volume of fuel BUT less energy (Horsepower).

 

You are correct but I believe the only time anyone would notice a horsepower loss from ethanol would be if we were at the drag strip or pulling a horse trailer in the mountains with our Vette. And even the drag strip would be iffy as wheel spin may change times.
Since your foot controls the amount of power (fuel delivery) to the wheels and the sensors just keep the engine running right, the entire horsepower argument is moot. Mileage will be slightly less for sure though.

 

Will I still be able to maintain the speed limit with a drop to 420.3 HP.???

 

Yes, but you may have to downshift to second gear.

 

Depends on how your car is geared and where it reaches peak horsepower. A6 @ 6,000 RPM in second might do it?

 

What - exactly - is "top tier" gas besides a marketing gimmick?

The same refinery supplies every gas station where I live. Sorry, I don't believe they really make "top tier" and lower grades at the same refinery with the same equipment stored in the same tanks delivered in the same trucks.

 

Most refined fuel is "fungible" , ie. generic at the refinery. However, additives including ethanol are added as trucks are loaded at the terminal. What you get at the local station is where top tier fuels comes in to the equation. At non-brand station, less additives while at top tier station, you get an additive package proprietary to that brand. You'll see trucks of all brands loading at the same terminal but what they're hauling is not the same.

 

Did you read post #8?
He knows more than most people, including you and I.

If you search under his user name, he has commented several times in other threads about the top tier certification process, and what the advantages are to your car.

He, and many others, have commented about the "same refinery same equipment same tanks" fallacy.

 

I use Shell V Power 91 ethanol free gas

 

Shell or Chevron 93 FTW in the LS3...Sunoco "93" seems to be a dog WOT...Hess 93 for the Acadia is tolerable.

 

Phillips 66 says right at their pumps that their gas contains 20% more detergent additives than required by the Top Tier standard.