3.5 V6 Atkinson Cycle engine and the gas grade parade extravaganza...

I disagree, instead I always believe a dog who wears sunglasses at night is smarter and knows more about octane than I do

 

my dog is awesome and possibly knows more about octane than I do.

 

I wish I'm a dog so I can get all of them bitches

 

If you can't measure the difference, then it is all feeling and nothing of substance.

 

The problem with what you are suggesting is that you are assuming "maximum" means better. In all truth, 93 doesn't burn as well as 87.... If your engine is tuned for 87 and you run 93, then the fuel will burn slower and be less efficient. Some engines have a high compression ratio and need the higher octane to prevent pre-ignition resulting in a loss of efficiency. The nice thing about modern engines is that they can compensate for running something different than optimal. They can't correct the compression ratio, but they might be able to compensate for it. When running too high of an octane gas, the engine might compensate by advancing ignition timing and making the engine feel more responsive off throttle, but at the cost of a loss of power in the top end.

So, unless someone runs a serious test and can prove it, running 93 in a truck designed to run 87 doesn't make it better.... it costs more money and it won't run as well.

 

I was actually going to bed when I stumbled over this thread.

Good article.

I never buy Citgo (7-11) gas b/c they are the US arm of the Venezuelan State Oil Company. Remember good ol' Hugo Chavez? I also don't buy Exxon as I'm still pissed over the Prince William Sound incident.

That would be me, The guy from Reno, NV & maybe the guy from Alberta

Generally speaking it is cheaper down here. 85 oct was $2.029/gal today in 80524. 87 is a 10 cents more & 91 is 20 cents more. E-85 is $1.649/Gal.

I noticed with a few exceptions the majority here is from an altitude of 4000' or less. This may clear up a little confusion. At altitudes above 4000' there is an octane shift downward. 85 oct up here performs the same as 87 at seal level. 87 up here performs the same as 89 at sea level. 91 up here instead of 93. It has to do with the amount of readily available oxygen. Less oxygen up here, lower octane which is also more explosive than higher octane.

Another point is Ethanol. All gas in Colorado is E-10. Again because of less oxygen in the air, it's made up for by adding ethanol. It's also mandated here as it helps reduce the air pollution from incomplete combustion which results in elevated levels of ozone (O2) & carbon monoxide (CO). (Denver's Brown Cloud)

Any vehicle intended to be sold in the US market since 1985 must be able to run with no less than 10% ethanol fuel. (google it) The easiest way to be in compliance is to not use cork or latex in gasket material since the ethanol will dissolve them & to treat engine parts to resist formic acid.

E-85 has a 105 octane rating at 4000' & above. My supercharger loves it, no pinging & not as expensive ($0.58/gal cheaper) as any other fuel especially the 91/93 oct that is required when using a 5VZ-FE supercharger. The 2 draw backs to using E-85 that I've noticed are slightly decreased fuel economy (about 10-15%) & higher engine temp. Before the s/c I could run all the time happily at about 180-195F. If I use straight E-85, since installing the s/c it hovers somewhere between 220-240F. I may get less MPG but my power is throw-you-back-in-the-seat noticeable. 0 to 60 is noticeably better than stock, but 40 to 80 is a completely different (motorcycle like) acceleration curve.

Until I get the TRD 160F thermostat, I either have to pay too much for 91 octane or blend my own premium at the pump. It's easier than is sounds BUT you must have an E-85 Controller card or a FlexFuel vehicle. So far, my blending target is about 93 octane, just in case my math is off & so the engine doesn't run above 205F. I've found that blending my own is between $0.25-$0.35 cheaper per gallon than premixed 91 octane.

**As a side note, figuring out the octane blending chart was the 1st time I've had to use algebra since High School. So for all you lying math teachers out there telling generations of kids you'll use it all your life, I'm going to use : Brian R :

 

@Husky Driver

Great information! I thought that the use of 85 at higher elevation applied more to carbureted engines? I obviously don't know much about this though.

 

The 91 octane 100% fuel is about $.50-.60 cents more than 87 octane with ethanol around here. Weigels in East Tennessee....About $2.69 compared to about $2.09 or so.

 

All right... You guys can say butt dyno until you turn blue in the face... I don't care.. today after a week of relatively poor performance in gas mileage as well as vibration while revving up (even though I'm still talking about 2000-2500 rpm, so not that much) I went to fill up an empty tank.. providentially they were out of 87... So I put my favorite 89... I could tell the difference the first half a mile... Smooth and back to my 20 mpg average... What can I say...

 

Now you need to fill up a tank with 85 to double-down on that vibration

 

How many miles did you drive with the 87?

 

About 380... 1 tank... But the difference can be noticed instantaneously!

 

It does, but carbureted engines have a problem with running (way beyond) too rich at altitudes over 10,500' because of the lack of oxygen. My '87 HiLux with a 2.4L 22R wouldn't restart if you shut it off when above tree line unless you rolled it & popped the clutch. At 12,000' I had to floor it in 1st gear 2WD to get it to run at all. The vast majority of people who still own carbureted will never have this problem. This is the road it happened on & with it being only 40 mi SW of my house, going above tree line (10,500'-11,000') happens fairly regularly. All of this becomes mostly irrelevant when you have fuel injection & a fuel mapping computer like the 22RE & newer/larger engines. *

Then you have the correct answer. Before putting on the s/c, my 2k4R owners manual & Hayes shop manual says I need to use altitude appropriate mid-grade (87 up here, 89 everywhere else lower) fuel. When I had run 85 in it I got the same results as you. Now the only time I use 85 in my tank is when mixing my own premium with 105 oct E-85, or not at all. Whenever you add a s/c or turbo to the equation you will always need premium (91 or 93) otherwise you can damage your engine. *

* Better explanations can be found here & here.

 

Sure, if the engine had adjusted to one gas, it takes awhile to adjust to a different gas. I don't know if one take would do it or not. I'd think so, but I'm honestly not sure. I know mine runs fine on 87.

 

Well the thing is the truck is so new I must have used a total of 4-5 tanks... The first one was 87 from the dealer... Vibrations and a 17 mpg average fuel efficiency... The second was 93 that I put... Much better on vibration and fuel economy and the third and forth were 89 slight vibration at higher rev and best fuel economy... fifth was 87 again and again was shit... and now 89... back to normal... I mean I am not a scientist and I'm not gonna write a dissertation on it but those are my facts...

 

all this is very interesting.......i have used Shell 87 for the first couple of months......then I tried Sams Club regular....ran good, same type of mileage but read it was not TopTier Gas....Then I have used Costco regular for the last 2 takes......run good and no noticeable differences....I have used Shell premium in my cars (Lexus) since 1995 and never had any issues and always can predict the mileage commuting for Irvine to San Jose at 104F, 80mph with A/C on and get 30-33mpg.....So, could i use it in the new truck.....but I use regular in truck....Costco is Top Tier and 25-cents lower in price.....I can't see any difference in either the cars using premium at 25-cents lower or truck using regular at 20-cents lower......So at home i will probably stick with Costco regular 87-octane and on the highway use Shell 87-octane in the Taco....I am happy either way

I use Shell premium only I'm my BMW R1200gs motorcycle though

 

I start using 89 for my 17 TRD Sport. collect the information (odo miles, galos of gas and price) and after 4 fuel up i calculate 19.2 MPG and a very smooth ride. now I'm testing with 87, I'm on my 2nd Fuel up and so far I'm getting 17.6 MPG and a loud knocking on the engine. I chose to use Shell fuel for this test.

 

Still relavent.

 

Also still relavent, still possibly throwing away $4 a month but still don't care

"I basically run premium exclusively and here is why - first off, my last 5 vehicles have been turbocharged Audi's that required it, so I am used to is - secondly, I put about 5,000 miles on per year, at 20mpg that is 250 gallons of gas through my truck per year. Premium is about .20 cents more expensive which means I am throwing away about $50 per year, aka $4 per month. And that is assuming there is zero added benefit. I honestly believe premium fuels with less ethanol are worth the extra $4 per month. I look at it as costing me one Starbucks coffee (I don't drink coffee so it offsets itself)."

 

Very interesting... you said that you get 20mpg using premium gas, is this a fact?
Because if it is a fact then you are saving money.
I'm still in testing period of gas quality vs mpg, and I'm getting only 17.6 using regular gas vs 19.2 using 89oct