Gas Octane

Nothing wrong with my truck as far as I can tell. It runs crisp and clean on regular and it doesn't on premium. Starts right up and pulls my boat real well. I have worked in refineries for nearly thirty years and spent much time in gasoline blending units working on process control analyzers, knock engines, reid vapor analyzers, and simulated distillation chromatography. I think I know a little about gasoline and what is in it. And having built several race engines I know a little about internal combustion engines also. My truck is running fine.

 

Did you happen to get all three tanks from the same station over the course of just a few weeks? Folks around these parts stopped filling up with higher octane blends when gas prices hit $4 and it seems they haven't started back yet even though prices are now much lower. Just out of curiosity, I talked with the fuel guy dropping gas at my corner store when he was there last week and asked him how often the station orders 91... he said it's once every couple of weeks or so lately but during the past year they could go a couple of months or more without ordering more.

 

I have been thinking, wouldn't 89 octane be the preferable choice in areas with only 89 or 93 but no 91? Octane levels above what the engine was designed for can rob power...therefore wouldn't you want to get as close as possible without going over?

 

Seeing both 87 and 91 has there + & -
I do the middle 89

 

Ran a tank of 87 over the past week after 93 for the past three tanks. Ugh. You never notice the difference until you move up.

It's odd, the exhaust is louder when using the 87 but the truck isn't as responsive. It's just as well...I prefer the lower, smoother tone I get when using 93...it's a lot more refined.

 

I would like to read those results, can you supply a link for us?

 

A month after I bought my truck, I read on here or some other forum that running 91 would get me better mpg and more power. I ran 91 for 5 tanks and saw basically no difference in MPG or power. In those 5 tanks I averaged 18.17 MPG. My average with regular (87) 4 tanks before was 18.02. My average with regular 4 tanks after was 17.75. So I saw a .15 MPG increase from before and a .42 MPG increase from after by useing 91. A fraction of a MPG is not worth the $20+ cents per gallon price increase from regular (87) to premium (91) for me. I suggest people try it though, it seems to work for some. But keep track of your MPG to see if it's actually worth it! Here's my MPG all time:
http://mpgtune.com/fillupHistory.php?carId=3296&period=last_year&fromDate=01%2F01%2F2000&tillDate=01%2F01%2F2035

 

i usually use 87, but when i went to the beach over the summer i tried 91 for a few tanks to see what it did, i think ill stick to 87 though lol

 

it says use 87 in the owners manual so thats all i use

 

ive been using 91 for over a year now and when i feel cheap and fill up with 87 i feel a difference, the acceleration is a hell of a lot slower when i get on the freeway, and i've tried this more than once, its just loud as hell and doesnt move anywhere, granted i have a K&N CAI and i'm running off the cats so that doesn't help, with BFG A/T i had about 12-14 MPG and now with the new BFG KM2's i have about 9-11 MPG but i like the sound, granted if i added the banks muffler back on it would get a hell of a lot more power and mpg but it would purr like a cat and i just can't have that haha

 

with the price drop on 91 octane, i go with that now.. heh.!

 

Didn't vote, but wanted to pitch in.

From the point I bought my truck I only filled up with gas from Speedway and tried my best to get it from one gas station, unless I went on a road trip.
Things I've noticed while using Speedway gas.

-During summer time I got better milage (18 mpg) out of 91 and better response from the engine.
-During winter I got better milage (16.5) out of 87, 91 gave me 15.5 mpg. I think this is due to the extra aditives they put into the fuel during winter time. The winters here in Chicago get pretty brutal.

About 6 months ago I was really low on gas (below E) and the only gas station for miles was Shell. Never used it before but didn't have a choice. So I filled up with 87. Within a 1/4 tank I noticed better reponse and a bit better milage. At my next fill up of 87 from Shell my calculations gave me 18.5 +/- (better than 91 from Speedway). Since than the only gas I use is from Shell. My last tank I filled up with 93 for the first time from Shell. So far I still have 3/8 of a tank to go and It already looks like I'll be at about 20 mpg. I still have to test the difference in Shell gas between 87 and 93 during winter.

P.S. 89 gave me the worst mpg.

 

85 oct here

 

I have been liking shell myself and can tell a difference in the butt dyno. I think the 93 octane shell does not use ethanol in the mix but that could mostly depend on the State

 

Quick question, what is a butt dyno?

I have to agree, I'm no gas guru or anything of that sort. The gas in the Chicago land area has ethanol in it. The only way I noticed it, is whenever I go to a diff state I get better milage on the same octane from the same brand gas station.

 

Ethanol sucks. Less energy density per unit volume and it is corrosive plus easily binds with water. All bad things for internal combustion engines.

 

Thank you for yet another clarification.

 

I just started putting in 89 into my gas tank. I will see how this effects my in-town MPG. The gas I have been using for the past several months was Shell 87, I am now using Shell 89.