Ethanol free 91 vs. 93 E10

reardiff · January 8, 2019

As the title says, for those with 6.2 if you had a choice would you use 91 ethanol free or 93 with 10%? I have been using 93 with 10% ethanol (or possibly even up to 15%) exclusively but now have a new local top tier gas station that offers 91 ethanol free. Owners manual says 93 or higher but wondering if you had the chance which would you choose and why? This is assuming you already made the decision to use premium so please no comments that premium isn't really needed, etc.. That topic has been beat to death already and not the intent of this conversation.

BillK01 · January 8, 2019

I’ll stick with my $2.57/gal 93 octane from Costco vs the $4.15/gal 91 ethanol free from the Citgo near me. I only spring for that expensive stuff in my Echo and Stihl weed wackers, blower and chain saws.

reardiff · January 8, 2019

Where are at to get 93 at $2.75? Here it's' just about $3.20

Also I should have mentioned the 91 ethanol free is about the same (with in a few cents usually) of the 93. So price isn't a factor.

Edited January 8, 2019 by reardiff

winn0040 · January 8, 2019

93 octane E10 is simply 91 with 10% ethanol added to get the additional octane. Would come down to price for me

BillK01 · January 8, 2019

7 minutes ago, reardiff said:

Where are at to get 93 at $2.75? Here it's' just about $3.20

Also I should have mentioned the 91 ethanol free is about the same (with in a few cents usually) of the 93. So price isn't a factor.

I’m in Western PA. The Costco I just filled up at this evening is in Cranberry Twp., PA and it was $2.57/gallon - by comparison the Get Go just up the street was $3.09/gallon (which more typical of premium prices around me). Costco’s gas prices are ludicrously good.

The ethanol free prices near me are always over $4/gallon.

Edited January 8, 2019 by BillK01

1SLOW1500 · January 8, 2019

The correct answer is on a stock truck it doesn't matter. The tune is built to adjust for ethanol so it both equal the same. to to command the same afr it needs a little more of the ethanol gas to burn right. Yes ethanol makes more power but un custom tuned and the stock torque tables in the truck not enough to matter. It's like saying you like your gas stations gas but are going on a trip, should you pack enough gas to get there and back in 50 gallon drums. Also the fuel economy is another thing some see small improvements in highway mileage but again cents at best. Do what ever you like.

Grumpy Bear · January 8, 2019

https://www.researchgate.net/figure/Effect-of-ethanol-blending-on-the-air-fuel-ratio-at-different-engine-loads_fig1_282877799

Nitrousbird · January 8, 2019

8 hours ago, reardiff said:

Where are at to get 93 at $2.75? Here it's' just about $3.20

Also I should have mentioned the 91 ethanol free is about the same (with in a few cents usually) of the 93. So price isn't a factor.

Premium @ Costco is $2.19/gallon here, with most others in the $2.3x range.

The question of 91 vs 93 is "knock." You will always make the most power (whether you notice it or not) running the lowest octane that does not having any knock being pick up by the knock sensor resulting in the ECU retarding timing. If the truck can do that on 91, that's your best bet in the situation from a power standpoint AND mileage standpoint, as gasoline has more energy in it than Ethanol, so you should technically see an increase in fuel mileage.

The real world answer, you would see no difference in a stock truck and little to none even in a modified tune.