Regular vs. Premium

[NeilBlanchard]

Hello,

As I understand it, there is actually less potential energy in higher octane fuel. So, if you don't need it to prevent knocking, then save your money.

[MetroMPG]

Originally Posted by RH77

Which parameters to choose?

Even if you could compute FE from the params, would you be confident you could distinguish a few percent difference, if any, by switching fuels?

Unless you burn a LOT of fuel driving the exact same route day in & day out, you're facing the same data reliability issues everyone has who wants to test fuel and/or additives.

That said, by default, I think I'd probably go with regular in a car with a knock sensor.

[RH77]

Originally Posted by MetroMPG

Even if you could compute FE from the params, would you be confident you could distinguish a few percent difference, if any, by switching fuels?

Unless you burn a LOT of fuel driving the exact same route day in & day out, you're facing the same data reliability issues everyone has who wants to test fuel and/or additives.

That said, by default, I think I'd probably go with regular in a car with a knock sensor.

Good points.

The vehicle is a commuter for my Wife (to work and school both), who has the same route except for the weekends. I would say she fills once a week -- FE is pretty stable at 29-31 this time of year (unless I drive it ). If it dips down to 27 or 28, then it may not be worth it (which is what happened during Winter). But Winter is Winter, as we know.

So, should the ECU be reset for such a change, or would that make it an unfair learning curve for a baseline?

We'll fill up with Reg next time 'round and see how it goes.

RH77

[jesse.rizzo]

Just to further complicate things, the octane rating on the pump is the minimum octane for that grade. there is no rule about them selling a higher octane than stated. In states where ethanol must be blended in 5 or 10 percent with regular gasoline, the "regular" might be the same octane as the mid grade or premium.

[gteclass]

higher octane gas also lets you run at a lower rpm without lugging it. On 87 my mirage wont do 35 mph in fifth. But with 89 or 91 it will do 30 no problem, of course till i get to a hill, but it will still creep up most hills at 35.

[MetroMPG]

Rick: I don't think there's any need to reset the ECU - a knock sensor is an immediate reaction type of thing.

gteclass: good point if you have a manual transmission.

[tjts1]

Originally Posted by jesse.rizzo

Just to further complicate things, the octane rating on the pump is the minimum octane for that grade. there is no rule about them selling a higher octane than stated. In states where ethanol must be blended in 5 or 10 percent with regular gasoline, the "regular" might be the same octane as the mid grade or premium.

Bingo!

Local tv station did a report on this about a year ago. They took samples of 87 89 and 91 octane from a number of local gas stations to a lab to be analized. They found all the samples tested between 90-92 octane with anywhere between 10-15% ethanol content. All the gasoline came from the same refinery and the only variation was the ammount of ethanol mixed in.

[RH77]

Originally Posted by MetroMPG

Rick: I don't think there's any need to reset the ECU - a knock sensor is an immediate reaction type of thing.

gteclass: good point if you have a manual transmission.

Thanks Darin -- now I won't have to lookup the radio code . Also, I can force somewhat of a bog with the manu-matic shift, in 5th, TC lockup, and at the bottom of the speed band (I think it's 50 mph -- I don't drive it all that often, so not sure). I'll be curious as to how it "acts".

Originally Posted by tjts1

All the gasoline came from the same refinery and the only variation was the ammount of ethanol mixed in.

So do they use Xylene anymore? I used to "make" my own racing fuel just by adding xylene to a tank. I was told (at the time -- 2003) that each brand dumps their own additives into the tanker truck just before it leaves for the stations.

What I find interesting is buying gas in the State of Iowa. Mid-Grade is the cheapest (often by 10-20 cents) because it's 10% ethanol (and likely subsidized). 87-octane is the next most expensive, followed by 91.

The first time I saw it, I thought they were having a "Sale" on mid-grade. I don't know if folks remember, many Amoco stations used to have all grades the same price on like Tuesdays or something.

Truthfully, I haven't been bold enough to try it to see if FE plummets (plus, I've been turned off by the current ripple running through the world as a result of ethanol production (and locally with . I do a lot of driving in Iowa

Maybe I'll give it a shot on the mid-grade to see what happens. I often hear of a certain percentage of Ethanol being a good thing for FE.

RH77