Pandora's Box... OPEN...

Man, you're going to get all sorts of opinions on this one. I've had people swear until they're blue in the face that they get better MPG with premium. I heard people say they notice a difference in power too. My experience has always been inconclusive. No noticeable power or mpg increases.

Keep in mind that the only difference between regular and premium is the additives the refineries put into the base fuel. All gasoline starts out the same. The only difference is what the particular company puts in the fuel and what they're aiming for. It also depends on the area of the country, as certain areas have seasonal blends.

If you want to spend the extra money and believe there is a difference, then go for it. If I had a different vehicle that needed premium in order to prevent detonation, I'd definitely run it. I'm pretty sure the stock X isn't tuned to the point that it needs anything over 87 octane.

Of course, your results may vary.

 

4 tanks since November?? I wish, I run a tank a week and that's if I don't go to the mountians or 4x4ing on the weekend.
I've tried a few tanks of primium and didn't notice a real difference so I stick with good old 87.

 

Wastin' your money on premium gas......while it could've been spent on mods....

Stick with 87

 

87 all day every day

 

Tahoe:

At our altitude, running 91 is just a waste of your hard earned money my friend. At lower elevations higher octane will allow your ecu to run more timing without detonation = MOAR POWER! Being at 4500ish feet your VQ will never have detonation problems and will run the maximum amount of timing advance that the stock tune will allow, even on 85-87 octaneccasion5:

I used to run my 07 WRX here on 87 with no pinging. Still faster than all my friends who ran 91, with more money in my pocket to make sure it stayed that way:laughing3:

 

Your ECM is programmed for a certain octane. Ours for 87. Unless you have a programmer to reflash to a diff octane running higher octane does no good.
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Octane vs quality

I've noticed a bigger difference between quality of gas offered than octane rating.

87 from Stop & Shop or BJs will net me about 30 miles less a tank than say 87 from Citgo or Mobil. But you gotta factor that into the price, S&S / BJs is usually cheaper.

Thankfully I found a quality Citgo station on my way to work that's reasonably priced and gets me good milage on 87.

My X gets about 19 combined. Especially on winter blend gas. So 30 more miles per tank on 87 Citgo = ~1.6 gallons of gas saved over S&S / Bjs. 1.6 gallons * $3.65 = $5.80 difference. So if its $5.80 less to fill my tank at S&S or BJs, vs Citgo I will occasionally do that. Typically its not. I usually put in 17 gallons a fill, so that's ~34 cents per gallon less in price that lower quality gas stations would need to be to break even on the higher quality, non-discounted gas, at the same octane rating. I'll only do this if we have tons of S&S points to where its like 50 cents off a gallon. Which is quite a few weeks of grocery shopping.

As for 93, its useless if you are stock. I do have a 93 Uprev tune that does take advange of the higher octane. More power and better mpg. But again, even with the better mpg, the same math still applies. When 93 is over 40 cents more than 87 in my area it does not make "cents" (besides the fun of added power). In the summer I will run 93 assuming the window is smaller than 40 cents to 87.

 

You should get better gas milage with the higher octane gas, trust me, I'm an engineer (or at least 2 semesters from graduating) here is the formula..

Fd (drag force) = 0.5pAv^2Cd where p is density of the fluid you're traveling through (air hopefully), v is the velocity at which you're traveling, A is the frontal area of the X, and Cd is the coefficient of drag.

Now, the higher the Fd, the more drag and more gas you will have to burn to get power back.. so.. if you lighten the load of the X (aka spending more money on gas and your wallet is LIGHTER) that will yield in a decreased friction force with the pavement. SO, with all the forces added up, wind resistance, friction forces, etc.. you should get slightly better gas mileage due to having a lighter wallet

 

Ryan: So funny, you engineers . . . .

Here in Colorado, we are one of just a few states that uses 85-octane as our regular gas, and the mid-grade is 87. Premium is 91. http://www.aaa.com/aaa/006/EnCompass/2007/mar/mar_AutoTalk.htm

I remember from when I lived in Illinois those numbers were 87 - 89 (or maybe 91) - 93.

My owners manual for the 2012 Xterra calls for a minimum octane of 87.
I buy my gas about 95% of the time at Costco.
They only offer 85 and 91 octane.
Their price on the 91 octane is within a couple of pennies of the 87/mid-grade at any other gas station.
So, I put in the 91-octane at Costco for roughly the same price as 87 octane would cost me anywhere else.
I've never put a tankfull of anything less than 91-octane in my X, don't know if there'd be a difference or not, just don't want to take any chances with 85-octane, even though they say that with our higher altitudes the 85 will work the same - I don't trust the API.

So, marshall9779 - what you're saying is that if I change the engine timing to allow for the 91-octane "burn", I'd get more power and efficiency? How easy is that to do by the "stealership"?

 

You failed to account for the lack of mods your truck will have due to you spending more on fuel which means in the long term your X will stay lighter for longer.

 

Very good point! I forgot to account for the lack of modding funds

 

I'm an engineer to. To see any benefit from higher octane gas you have to change yor timing allowing for a longer burn thus more power and efficiency.
The formula you put out has nothing to do with fuel octane. I minored in motor sports and the engines class I had was basically thermodynamics on crack.
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Repeat using a Foghorn Leghorn voice - It's a joke son

 

Most programmers allow you to change tunes for diff octanes. Superchips, Bully dog, etc.
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2005, 2006 & 2007 Xterra's, have different ECU settings than later models and will benefit from higher octane by changing timing/injector pulse cycle until it senses knock. They can also benefit from tuning more than later models. How much of a benefit is hard to say, too many variables; altitude, humidity, air temps, fuel additives, etc.

 

So I've only run through 4 tanks of gas since I bought it in November (good or bad depending on which angle you look at it) and I've read some threads on here on the premium vs. regular.

4 tanks since November???? You got to be ****ting me!
I run through a tank in about a week!! uke:
Granted it's my daily and I drive about an hour a day.. but still.

Have yet to try this so-called 91 gas but I've heard it's magical and expensive!

I'll just stick to my "just getting by" 87 gas.

 

Run Premium. support Alberta (oil sands) and you support the AXE crew.

nah but for real the only time i've noticed a difference with premium is on the coast when I happen to be towing something. And i'll only fill up with it when the gas station runs out of regular and starts selling premium at regular prices. which is often, for some reason.

 

87 here. 250+ MILES A WEEK. Or one tank a week. Never tried 91.

 

I tried premium for a few weeks, it only got me another 15 miles to the tank with no (by the butt dyno) change in performance. Not worth it to me.

 

What about using 100% gas instead of the 90/10 ethanol gas, has anyone noticed better mileage? Ive never noticed better mileage but my dad claims it makes his truck run smoother, but I think it depends on the engine/vehicle

 

wow... what a response to that question. Yeah I know that I've heard the same arguments over time as I have friends that swear by premium, and others that think its stupid. I've never really had a high performance car that specifically recommended or required higher octane, until the Xterra.

I know that yeah visiting Colorado in the past I could run 85 octane no problem in other cars, so maybe I'll go back to 87 here.

As far as only 4 tanks, I have a company truck that I drive daily and put tons of miles on yet (had it for 9 months and have 16k on it already). The Xterra just plays on weekends if at all... sometimes it sits for almost 2 weeks... although my wife is taking a liking to it more lately and it seems to be racking up a couple of more miles here lately! :scratch:

 

I've never really had a high performance car that specifically recommended or required higher octane, until the Xterra.

Que?

No higher octane required in the X.

 

I thought the owners manual "recommended" higher octane for optimum performance??? Did I dream that up? I'll have to go back and look tonight...

 

I ran 87 until i installed a Bullydog GT. i run premium now but that's only because it is recommended with their tune. You're talking about a 4 dollar difference per tank. it's really not that much

Here's a little tip though. if you're buying fuel from a place that doesn't need fuel deliveries weekly, than the High octane stuff is gonna lose a lot of it's pop and end up closer to Reg because it's more likely to be sold less often.
For that reason i fill up within a day or two of delivery when i can. I can see the difference in Mpg in real time with the Bullydog GT

 

I'm with you on the 93 octane thing, if you have a tune to take advantage of it and you get better mpg to make up the cost difference. 93 is usually a .35 cent different between 87, at least in my area. That's closer to $7 more on a fill (I fill over 19 gallons). That's almost $30 a month. And $7 more per tank, is close to 2 gallons more of 87. Times that by your avg mpg (mine is 19) that's 36 more miles my 93 tank needs to go over an 87 tank to be worth it.

Which suprisingly it is. I can squeeze out close to 21 avg on my 93 tune (on summer blend.)

I'm completely lost though on filling up close to delivery? Are you suggesting that the 'octane' settles to the bottom??

 

I can't tell much of a difference between regular and premium. It does seem to run slightly smoother, but it doesn't get any better MPG. However, I do run a tank of premium through every several months on a roadtrip. Could be wasting my money, but I've always heard that its good for the fuel system.

 

For fuel economy 87 octane and light throttle is the best bet. In high heat and when towing higher octane, using 91 octane instead of 87, performs better. A couple summers ago I was pulling our travel trailer with our 06 up a 5% grade in 108 degree heat using 87. As soon as the engine was under full load you could hear detonation increased and immediately power dropped due to ecu adjusting. The next trip I filled up with 91 and she kept constant power all the way up the grade. This is an extreme, I know, but the engine will try to keep the mixture and timing so the engine is on the verge of detonation, where optimum fuel burn is taking place. So if you need pulling power in the summer time, higher octane will provide better results. If you want high gas mileage, lower octane and be easy on the throttle.

When I had a Superchips Tune, I never got good mileage, probably because I couldn't keep off the skinny peddle!

 

^ Random side note, but I'm digging your avatar. Especially when it appears next to mine on threads. I want to change my name to: 'iamamused'

 

LOL! I've had that avatar on my PC for a while and forgot to change over to it, then in one thread I saw yours and remembered! iamamused would be awesome!!