What Octane do you use?

I was wondering if you all have noticed a difference in gas consumption between Regular (87) Mid-grade (89) and Premium (92) fuels.... this is a purely "eyeball/guesstimate" reading, but the XK is currently being used as my primary work vehicle, no other trips or errands, and if I use regular, a full tank will last exactly one week. However, if I fill up with premium, I am able to get almost exactly two weeks use! Yeah I'm paying more for premium, but I feel that I'm getting alot more benefit from it vs. regular... What's you guy's opinion?????

BTW, I'm running the 3.7L (4X4) with K&N drop-in air filter, RC 2.5" lift and Mickey Thompson 265/70/17 Baja MTZ.....

I've done tests on my wifes car before and did get slightly better mileage on the premium just enough to cover the extra cost but double the distance makes no sense to me.

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Originally Posted by Sal-XK

I've done tests on my wifes car before and did get slightly better mileage on the premium just enough to cover the extra cost but double the distance makes no sense to me.

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Like I said, its not an "exact measurement", I have not yet done mpg statistics or written down every single red light that I encounter; but the wife can easily back me up and say the same... I will be doing a test soon though, when I have to fill'er up again, i'll use regular, and then premium the next time...

I know its hard to an accurate read on the results with so many variables and stuff. I did my wife's car while on a road trip so it was a little easier and more straight forward test all highway miles. But if you can at least take the same route to and from work on two separate tanks gas you can at least get an average. Like I said I did experience a gain in mileage which meant I had to stop less for fill ups and I did get more then enough mileage to pay for the extra cost. Also I think the XK is meant to run on 89 octane so I'm curious to see what you get out of it. Looking forward to your results.

I used to use premium exclusively and when I purchased the Superchips I changed the settings and now run 87. If you use a program like fuelly in my signature it will help monitor your mileage.

I run the mid grade,it's only like .10cents more then regular.. I'm getting 240miles to a tank with about 3 gal.left in the tank.. I noticed with the midgrade it seems to run smoother too ..Regular made it feel more "draggy"..

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Originally Posted by 06blkhemi

I run the mid grade,it's only like .10cents more then regular.. I'm getting 240miles to a tank with about 3 gal.left in the tank.. I noticed with the midgrade it seems to run smoother too ..Regular made it feel more "draggy"..

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Not bad for a hemi... I like to fuel up with premium and dump a bottle of seafoam when we go on trips.....for some reason I was under the impression that the XK's had a 5 gallon "Reserve" ....

I have a 4.7L flex fuel. I conducted an extremely unscientific couple of tank average using E85 (85 octane ethanol). I know it is not a direct comparison to fossil fuels, but here's what my averaged numbers at the time told me -

A tank of E85 did not give me as many miles per tank, but was about 30 cents a gallon cheaper.

A tank of 87 octane gas got me more miles per tank, but cost about 30 cents a gallon more.

I don't have my numbers anymore, but after the math, my price per mile for fuel turned out to be statistically the same, within the margin of error for my methods. Since I don't like to stop at filling stations, and the E85 station is not easy for me to get, I almost exclusiely burn 87.

While towing, I have noticed that I don't seem to have to bury my foot in the accelerator as much climbing hills with 89, so occasionaly I splurge there. I have never run real numbers on MPG doing that, it is just an opinion based on the subjective feel of the gas pedal.

Ok, so I filled up at Sam's Club after returning from work with 93 octane today, got 44950 miles on the mileanometer, let's see how this goes....

I run only 89 or better. WanderingT's - 30 cents is not nearly enough of an offset to justify E85. I experienced an average 2mpg decrease with E85 when I decided to test it out. So back when 89 octane was running $3.00, I calcuated that E85 had to be no more than $2.40 to justify. Now I did feel a lot better throttle response with E85, but I am sure that was becuase it has a 105 octane rating. E85 is great for cars specifically designed for it bc the exhaust temps are cooler so you can theoretically crank up the compression and actually get more HP, but Flex fuel cars don't do that, they just change the firing, etc. Make sure that if you DO test you go through at least 2 to 4 tanks for the electronics to fully kick in.

Higher Octane will not improve your MPG all by itself. However, E85 is not the same as using lower octane because it
does get less MPG and HP.

I have used E85 a couple times, you get less mileage and less power, and you pay less. But it works out about the
same as far as costs go. Spend less but more often.

I think E85 is a waste of resources. No corn is going to waste so we can't say it only uses excess corn etc.

I believe we do need to experiment with it and other possibilities. Maybe one day they will find a way to make fuel cost
less and get better MPG. That will be the day after pigs make regular flights from Toledo to Cincinnati unless the Fed
finds a way to replace lost tax revenues and oil companies don't loose thier axx.

Can we use hydrogen?

I use 87 most of the time. Once in a while I use higher octane.

Most people do not realize how big the corn industry really is. They put corn in almost everything we consume now. From the cow that is force fed corn feed to the drinks that has corn syrup in it. Do to governmental intervention in the 50's we now grow way more corn then we need or can export. There are tons and tons of corn that sit after harvest. There is a great documentary on Net Flix about this I encourage you to take a look at it. In fact if you have net flix you should visit the documentary section and check them out like beer wars and the walmart one it can really open your eyes.

we could always make more sour mash whiskey...... just a thought.

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Originally Posted by strokeZ

we could always make more sour mash whiskey...... just a thought.

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Hmmm, I'd like to try some of that...

Anyway, experiment went bad when I had to take several unexpected trips across the Valley...I was gonna get a pic of my odometer and fuel guage at 1 week (exactly half full, or half empty if you are the negative type) but that also went to crap as my memory card was full...

The octane rating of gasoline relates to how difficult it is to "set it off", in a controlled manner, in your cylinder... The higher the number, the harder it is to "set off". If the compression in your engine is high, the likelihood of a premature ignition rises (it ignites on compression as opposed to the spark plug igniting it) and a higher octaned fuel should be used to prevent this pre-ignition combustion of the air/gas mixture (knocking). Octane does nothing for mileage...it just makes it (the gas) harder to ignite. The best gas to use, would be the lowest octane number that you can use that doesn't pre-ignite on compression (engine knock). I had to run high octane in 66 Chevelle, but, I was running 11.7 to 1 compression (milled and ported heads on a bored and balanced block). On my Hemi Commander, I use 87 octane. I've used 89 and 91 when towing as an experiment, even though I wasn't getting ignition knock on 87 and found absolutely no difference in performance or mileage, even when towing 6000 lbs through the Rockies. I use 87 now, all the time. Until I start getting pre-ignition, I find no reason to pay the "toll" for higher octane (anti-knock) gasoline.