Fuel Tips: The Science of High Octane

Great information. Very helpful.

I wouldn't say that premium should be ran in all 87 recommended engines, but it doesn't hurt and I think it will clean it but I only run 93 maybe a couple times a year in my "87" vehicles, and run them hard with that tank!

It's always funny talking to non car people (or the car & driver mag readers that think they are car people) that say 93 is all hype and you don't need it even if it says recommended on the cap. And when you try to explain engine compression and how most modern engines are high compression, and that most companies have to add the 87 fuel maps to pull timing since they know people will be cheap and put swill in the tank. Any of my "premium recommended" cars make a big difference in how they drive, even the transmission shifts at better RPM's in my Yukon.

In reply to StuntmanMike : what I fail to understand is why focus on 91 or even 93 octane when ethanol is 114 octane.  

Yes I understand there is less energy in alcohol then gasoline  but there is less energy in gasoline then diesel.  

So is octane the holy grail or is energy?  Either case gasoline loses .  

In reply to mad_machine :

I spent quite a lot of time watching the engine on my old Dodge Dart 1.4 turbo with the Torque app for a variety of unrelated reasons, and I do have to say that running 91 octane vs 87 made a BIG difference. The difference in gas mileage was pretty significant (3-4 mpg), but the amount of boost was also a lot higher. That extra boost really made a difference with the butt-dyno. (And if I hadn't enjoyed that so much I'd probably have seen even more improvements in the gas mileage.)

mad_machine said:

It is my opinion that most modern cars can benefit from higher octane fuels. I know the manual and the flap over the cap says you can run the cheap stuff, but it has been my experience with even cheap cars that the adaptive engine management on new cars can make the most of higher octane.

 

For instance, I had a 1999 Hyundai Tiburon. With it's wheezy 135hp, it was not a big performer. It got epa rated to 30mpg. I consistantly got 35mpg, much more so than most people in the forum that was attached to the car. I ran 93 octane. I tried the lower stuff to test, and my MPGs would suffer as a result. In the end, I will admit, it was a wash as far as money to miles driven was concerned. Spend more at the pump and go further or spend less and have to fill up a little more often. The money evened out.

I never raced the car or dynoed it, but I always wondered if I had a few more ponies under the hood on 93 octane as the management more fully advanced the timing

When dealing with octane and mileage, please remember that ” your mileage will vary”  That’s just a polite way of saying there are some lousy drivers out there.  If you get better than reported fuel mileage how much is due to your skill? And how much due to the fuel? 

StuntmanMike said:

I wouldn't say that premium should be ran in all 87 recommended engines, but it doesn't hurt and I think it will clean it but I only run 93 maybe a couple times a year in my "87" vehicles, and run them hard with that tank!

It's always funny talking to non car people (or the car & driver mag readers that think they are car people) that say 93 is all hype and you don't need it even if it says recommended on the cap. And when you try to explain engine compression and how most modern engines are high compression, and that most companies have to add the 87 fuel maps to pull timing since they know people will be cheap and put swill in the tank. Any of my "premium recommended" cars make a big difference in how they drive, even the transmission shifts at better RPM's in my Yukon.

We are ignoring the elephant in the room here.  That is cost per mile.   If the difference in price exceeds the increased cost then you are not gaining but losing.  

Right up to the point where performance priority exceeds the priority of cost.  On track performance wins. On the street, at least when mundane tasks such as commuting, grocery shopping, taking kids to soccer, etc. cost must win. 

At least if you are on a budget like most people. 

Larry said:

The big factor ignored here is ethanol. Ethanol degrades fuel faster than the gasoline degrades, despite increasing octane equivalent rating.  93 octane pump gas is typically 91 octane gasoline with ethanol added. Ethanol-free 91 octane gasoline will last longer than 93 containing ethanol, despite the lower rating.

Valid if storage is your priority.  In the past I filled my tank often more than once a day. Today in semi retirement it’s reduced to almost weekly.  My collector cars and my race car are stored with little or no fuel and what fuel there is is treated with fuel stabilizer. 

So fear of Ethanol loses any impact with me. 

I use math*  to decide if I want to save the money with  the lower cost of ethanol.  Although to be honest there are times when the added power offered by Ethanol wins out just because I enjoy turning  the vehicle into a giggle machine. You’d think at my age (71) I’d grow out of that by now.  

Right now 92 octane non oxygenated is $3.29 a gallon and E85 with around 100 octane is $2.09 

E85 costs me roughly 2 mpg (depending on how much I want to be cheap and how much I want the performance improvement). 

So I I save $24 a tank but can only  360 miles per tank instead of 400. 

Lots of anecdotal evidence here, so I'll add my two year experience with a 3.4 Tacoma running a TRD supercharger.

No fuel or tuning modifications, since it was dealer installed. At that time, the official line from Toyota was that the blower would require no tuning, so if I did any tuning modifications it would have voided the warranty.

I tried multiple different brands of 93 octane gasoline and it had a part throttle ping with every one, except Shell. It ran perfectly fine with Shell in the tank.

BTW, after I sold the truck, Toyota added a 7th injector to the intake ahead of the throttle body as part of the kit.

Floating Doc said:

Lots of anecdotal evidence here, so I'll add my two year experience with a 3.4 Tacoma running a TRD supercharger.

No fuel or tuning modifications, since it was dealer installed. At that time, the official line from Toyota was that the blower would require no tuning, so if I did any tuning modifications it would have voided the warranty.

I tried multiple different brands of 93 octane gasoline and it had a part throttle ping with every one, except Shell. It ran perfectly fine with Shell in the tank.

BTW, after I sold the truck, Toyota added a 7th injector to the intake ahead of the throttle body as part of the kit.

While localities differ around here Shell gas comes from either the Koch refinery or the Ashland refinery.  Those are the only two refineries within hundreds of miles.

  Only 5 refineries are located in the US but the site didn’t point out which refineries produced gasoline and which produced chemicals and other products.  

So buying fuel via the Brand is not likely to get you any difference since there are plenty of gas stations even in my city that sell Shell.