Advantages of "Premium" Gas/Petrol

I typically zip along at 9mph over the limit on the highway, but only get about 35mpg driving at 79mph.
When I was headed home and hit Ames, IA I had to slow to 74 and decided to maintain that and reset my trip odometer and was shocked to register nearly 40mpg. Then when I got to Des Moines I slowed down to 70mph and got a reading of 44mpg.

I didn’t think the difference would be that much. I shall have to do further testing in the future and possibly drive more slowly. A 5.1% reduction in speed (from 79 to 75) resulted in a 14% increase in mileage and an 11.4% reduction in speed (from 79 to 70) resulted in a 26% increase. I probably need to do more testing to solidify those numbers, but it will make me agonize over the optimum arrival time & gas cost.

There was a stiff southerly breeze along I-35 this weekend…fwiw

I do find a huge change in fuel efficiency by using higher octane (and zero ethanol if available).

On the order of about 5 miles per gallon more.

(And as ### pointed out, wind direction can also have a significant impact on fuel efficiency.)

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Yup…that’s another factor

Car and Driver didn’t test the zero ethanol but found vastly more modest gains from higher octane, and in some cases the performance was worse. But they didn’t go lower than the manufacturer’s minimum.

I’m guessing zero ethanol makes a bigger difference than the octane. From what I can tell the bottom line is to go with the manufacturer’s recommendation on octane. (Based on past research as well as linked article.)

A lot of it is aerodynamic drag, which varies with the square of speed.

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Yep, I always beleived that higher octane made my vehicle more efficient, but turns out, it doesn’t. It burns more effectively, but apparently you don’t get more MPG.

Not enough to offset the expense, at any rate. If you’re trying to win the Indy 500 then sure, but if you’re on a family road trip, not worth it.

I should’ve added the qualification of “when driving long distances” . . . and the comparison is between the octanes and driving “long distances” (not “in-town” vs. “long-distance”). And my numbers come from my observations.

WRT to the linked article, the four tested are not “representative” of the population of cars, IMO. Three of them are “turbo”.

There is also the elevation factor, too, IMO. Put another way, “California emissions” engines will perform differently than “other emission” engines at different elevations. So I can see diminished returns on octane at lower elevation (richer O2).

Car & Driver did a 200 mile loop when they tested the fuel economy. That seems like a long enough distance to be “long distance”.

Aren’t most newer cars turbocharged these days?

I definitely don’t know enough about high elevation performance to comment on that piece. Sounds like they tested in the midwest, so if your assertion is that it would make a bigger difference at elevation that may well be true.

Perhaps performance variants are mostly turbo-charged, but most models, no, and certainly not most cars by volume.

Huh, I thought they were. The CR-V is not exactly a “performance model”, as an example. But I’m admittedly not a car guru… just an impression I had.

Hmm, I have some crow to eat. Turbos are more common than I thought. The last ICE shopping I did was on the smaller side, some sportier models did have. But in the mid size class, Honda moved to all turbo for the Accord a couple of years ago. Hyundai’s Sonata is turbo on higher trims, Camry, Altima the same. Chevy Malibu is all turbo. I suppose it is a smaller engine for fuel economy add turbo for more power combination. F150 has turbo on mid to upper trims.

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Yeah, I think it was when I was car shopping that a dealer made the comment that the manufacturers were moving to turbo… probably a Honda dealer, although I couldn’t say for sure. I don’t have a vivid recollection of the conversation, just that by the time I’d bought the car I had the vague impression that turbos were a lot more common than they used to be. I’m not even certain it was a Honda dealer as I did shop around a bit.

Re:octane. The octane rating is simply how much cylinder pressure it takes to ignite fuel. Higher octane rating means it takes more pressure, so you can run higher compression ratios and/or more boost. So you can get more power with higher octane by doing one or both of those. Higher octane fuel doesn’t contain more energy per unit volume, in general.

Octane really comes into play (for turbo engines) when boost is high and you’re forcing a lot of air into the engine. That’s when cylinder pressure goes way up and the fuel can ignite under compression. Driving at 70mph doesn’t really do that. And that’s why I used to put 87 octane in my Mazdaspeed3 for road trips. Cheaper gas, same mpg, and I wasn’t going to push the engine hard enough to require more octane rating.

Re:turbochargers. Turbos are becoming insanely common. A 2.0l turbo really hits the sweet spot for so many applications, in terms of engine size, power, and mpg. You can easily get 200-250hp, and 250+ torque, and that torque comes on at low RPMs. Audi has a 2.0t, and BMW, Lexus, Honda, Hyundai, Ford, the list goes on. They go in compacts, full size cars, SUVs galore. Hell, Land Rover and Jaguar have them. VW puts a 2.0t in the Atlas, an SUV with three rows of seats.

I don’t know if the majority of vehicles are sold in the US with turbos. We buy a LOT of trucks, and those buyers still seem to prefer a big V8. If not, then I suspect within a few years, turbos will outnumber NA vehicles.

Seems to be enough interest that I’ve split out this conversation into a separate topic.

I think that this is true of “new” models; not necessary true of the vehicles on the road today–which was my point.

I would say that driving in the mountains of Colorado, boost is very likely to be engaged on the interstates and major highways.

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I thought the general advice was that it wasn’t worth it unless you need it. My car requires it so I buy premium, but otherwise I would just get regular.


Fair. For ‘most’ interstate driving, not much boost.

My car is a 2016 with a 4 cylinder turbo. For the 2015 and prior model years, the manufacturer said premium gas was “recommended”. Starting with my model year, they said lower octane was fine. However, their published horsepower and torque figures for the 2016 model were done using premium. The engine did not change from 2015 to 2016, so this makes no sense to me. I normally follow whatever the manufacturer recommendation is wrt premium vs regular octane, but in this odd case I buy premium because that’s what the manufacturer said for the exact same engine in 2015 and how they tested the 2016 model.

The octane rating is a measure of “knock resistance”

Higher octane rating does not mean there is more energy content in a gallon of fuel.