Premium fuel with the 2.7?

I run 91 octane " premium" in my 02 double cab just because I'm running a supercharger and need the higher octane

 

Any ideas on how many tanks it takes before it adapts to the higher octane fuel?

 

I use non ethanol from a small commercial tank and it makes a difference in my 2.7 with better start up and smoother running. Mpg's are slightly better than when I buy from a retailer. I got the best mpg when I was in the mountains in Colorado last summer using 85 octane. Go figure?

 

I may be wrong, but I believe at higher altitude you need less octane.

 

Must be. I was up in vail at around 8000 ft and all they have is 85 for the first grade. Pushed the 2.7 pretty hard to maintain speed up the passes, so wasn't babying it. Got 23mpg average. I'm lucky to get 18 here in GA at 400 ft.

 

I felt like I saw a difference 1-2 maybe 3 full tanks later. It never felt "bad" in between just felt better by the end. Now I, as many, would claim I can feel the difference.

 

Just to be fair, I tried 91 octane ethanol free this time. About 5 gallons on top of 5 gallons on 87 octane e10 and my fuel economy jumped up way more than expected. (Looking at my Ultragauge) I may try a full tank to see how it goes.

 

Yep. I lived at 6500' 91 was the highest you would ever see and you can run high compression at 85. Now I'm at sea level, 91 is mid grade and 94 is everywhere.

 

I've got a friend of mine that's been hauling gas for over 20 years. He says if your going to run a cheaper brand of gas always get premium because it is more refined and has less garbage in it. I'd say all premium is more refined with less garbage in it. But then, that's just an opinion since I'm no fuels engineer. My 2.7 seems to run better on 91. Mileage only barely increases but it just seems to run smoother and has better throttle response. The improvement is so slight though that is is almost not even there. I do run premium in mine in the summer. 91 octane. In the winter I was running 87 last winter and will probably do it again this winter. I'm also at 7000 feet so 87 is really all I should be running but the 91 does "seem" to improve the way it runs and I "think" it's a little cleaner than the regular.

 

One tank probably isn't enough to let the computer re calibrate for the higher octane.

 

That isn't entirely true. Combustion is a CHAIN reaction. In order for the reaction to continue, the unburnt fuel needs to be heated enough to ignite. Higher octane means that it ignites at a higher temperature, which takes slightly longer to achieve since it doesn't burn any hotter. However, that isn't the objective of the higher octane, it is a side-effect.

Um, not quite.

The primary difference between preignition and detonation is WHEN it occurs.

Pre-ignition occurs BEFORE the spark (hence "pre"), triggered by a point source of heat somewhere within the combustion chamber. Aka, a "hot spot".

Detonation occurs AFTER the spark, triggered by the pressure waves that ripple through the air/fuel mixture AHEAD of the flame front.

Now if you think about it, you simply CANNOT stop preignition through retarding the ignition timing, because the ignition happens BEFORE the spark even happens!

But you CAN stop detonation, because detonation is triggered *by* the ignition.

So imagine this; your piston reaches TDC, the ignition sparks, the fuel begins burning. The pressure wave instantly blasts through the entire combustion chamber AHEAD of the flame front, somewhere ahead of the flame front, a compression wave triggers a second point of ignition. Now you have two flame fronts travelling towards each other. When these flame fronts collide, that is when you get a "ping". Now what you do to stop this from happening, is you wait a tiny bit longer until the piston starts its trip back down and the pressure is slightly reduced. NOW when the ignition sparks, the pressure isn't high enough for the compression waves to cause a detonation.

Note that dieseling can only be caused by preignition.

 

At higher *elevation*, you *don't need as high* octane. Subtle, but important distinction.

 

The difference between 87 and whatever is higher than it, has nothing to do with refinement. They ADD a combustion inhibitor to the 87 to turn it into whatever.

 

That's just what my buddy told me and it's probably hearsay. I do know that they add Butane to increase the octane when they make premium. How that works I have no idea but I know that for a fact since I hauled propane and butane for a few years. They also add butane to propane in the summer time for use as a automibile fuel.

 

I put almost 300,000 miles on a trd off road using the cheapest gas I could buy every tank, never had an issue.
Pretty sure these engines and most modern engines are designed to run the cheap stuff.

 

I suspect you're probably right.

 

I've been tracking my fuel mileage since I bought the truck two years ago. I almost always run mid-grade fuel (89 octane).

I have run 87 octane for weeks at a time as an experiment to see if the higher octane actually made any difference.

I generally get 2 mpg more using mid-grade over regular.

 

Yes most modern gasoline engines are designed to burn 87 octane "regular" grade, which might be 85 octane at elevation. Point being that premium is not required.

I'm happy to hear of the mileage and (assuming) good performance you got from plain old regular gas. And like you, I'll probably get minimum 300k miles burning regular the entire time

Indy said the manufactuer's minimum octane requirements have a buffer built in, which is true. If I fill up with 85 octane (at elevation) and then drive downhill to a much lower elevation where regular grade is sold as 87 octane, my engine is not going to explode running the 85. Whether it's ARCO, Safeway, Rotten Robbie, Farmer John's Gas & Go... these 2.7 engines will burn just about any gas, crap or otherwise. I even had a couple gallons of very old yellowed gasoline from a dirt bike I hadn't ridden since April. Drained the bike and poured it into the Tacoma (which had about 1/4 tank) and it ran just fine. Sure it wasn't much, I'm just saying it made literally zero difference in the engine's normal operation. Love it!

 

My truck may just be odd. I loose about 5 MPG with 87. Using premium (93) or mid (89) I see no difference in performance or MPG so I stick to mid grade. Borescope inspection recently showed a very clean combustion chamber and the back of the valves were pristine after 194k.

 

I'm not an expert, but wouldnt higher octane fuel allow timing to be advanced further than 87 which would equal more power.

I live in the mountains and tried 91 and was amazed that it pulled the 7* grade and actually accelerated, normally I would slowly loose speed till I got to the top.

Ran 91 for 10 tanks then thought maybe it's just me, and switched back to 87. Truck went right back to loosing speed on the grade.

I've been running 91 ever since. Mpg has been unaffected, and flat land driving is pretty much the same.

Maybe on the 3rd gen 2.7 it is different. But I'm pulling 35's right now, and it's not ideal with stock gearing, but I keep up with traffic no problem.