flex fuel question

[CountryBoy19]

If the stuff is cheap enough where you live, it's ok to mix it as you wrote initially in your FlexFuel engine. You'll get slightly lower mileage and a lower fuel bill as well.

My closest pump is not around the corner but it pays to run the stuff, I save $12 every 300 miles at current prices right now.

Just keep in mind that ethanol has only 70% of the energy as gasoline so E10 (regular pump gas) has 97% of the energy of ethanol free gas, and E85 has only 74.5% of the energy of ethanol-free gas (76.8% of what E10 has). Assuming same efficiency running both (I haven't seen evidence that there is an efficiency boost from E85), the price of E85 has to be less than 76.8% of the price of regular pump gas to come out equal.

That is just for informational purposes for anybody not in the know. If you have E85 available and it's working out better for you then I say go for it. I simply don't have it available to me.

 

[swathdiver]

What do you mean by efficiency?

For my purposes, I do not consider low octane fuels at all, they are not even close in performance (my vehicles) so my comparisons unless otherwise stated are always 93 versus E85. A few months ago it still cost less to run 93 than the lower octane fuels because of their poorer mileage; their cost per mile was more. For the last ten months, E85 has cost me $.04 cents less per mile than gasoline, about $12 saved for every 300 miles driven.

 

[CountryBoy19]

What do you mean by efficiency?

For my purposes, I do not consider low octane fuels at all, they are not even close in performance (my vehicles) so my comparisons unless otherwise stated are always 93 versus E85. A few months ago it still cost less to run 93 than the lower octane fuels because of their poorer mileage; their cost per mile was more. For the last ten months, E85 has cost me $.04 cents less per mile than gasoline, about $12 saved for every 300 miles driven.

Efficiency = miles/gallon

If you don't consider low-octane fuels for whatever reason, then the numbers work out even more to your advantage. I was simply trying to supply information to anybody reading the thread. There is an all-too-common myth surrounding ethanol fuels that they're amazing efficiency enhancers when they are not. Ethanol has a very high octane so ethanol blends are cheap octane boosters but your efficiency (miles/gallon) suffers because of the reduced BTU/gallon in ethanol. I was trying to point out the less-often considered efficiency numbers of cents/mile.

All that being said, is your ride built/tuned? I don't know a lot about the NNBS (assuming you're talking about the ride in your signature) but isn't it meant to run on low-octane with the 5.3L? Unless it's tuned/built to run on high-octane I don't see how you're getting better mileage and/or cents/mile running E85 vs. low-octane or 93 vs 91 or lower. The gains from running high-octane fuels aren't usually high enough to offset the cost unless your engine is made/built to run the high-octane stuff.

ETA, my brother has a NNBS Denali with the 6.2L. IIRC that engine should have mid or high octane fuel. He said he gets only marginally better mileage, but much better performance when running mid-grade over low-grade, he pays a marginally higher cost/mile to run the fuel he is supposed to run.

 

[swathdiver]

Efficiency = miles/gallon

Got it, I think we're on the same page but would say a better indicator of efficiency is cents per mile.

Since the 1980s I've used my little memo books to record the mileage I was getting with various brands and octanes with everything driven for any length of time. ALL of the cars benefited from running high test gasoline rather than low no matter if it was a little Hyundai Excel, Toyota Corolla or a Delta 88 or Buick Regal and so on. With a Pontiac Montana, it would get 8 mpg on Mobil's 87 or 12 mpg on Mobil's 93 in delivery mode for example. Last year it cost slightly more, within tenths of pennies to run 93 over 87, hardly a reason to switch.

Since October, a ten month average shows that it has cost $.19 cents a mile to run E85 or $.23 cents a mile to run 93. At some point I'll hold up my nose and run the lower octane fuels and see what kind of mileage they get, unless a couple others want to do it for me and post the results! Ken is running 89 in his truck and comparing it with E85.