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- Thread starter edcamp
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I have auto engine start/stop deactivated, I’m getting about 19mpg on 91 octane (highest available near me). When I drove the car new from TX to WA, I couldn’t get access to higher octane gas in some states and saw a slight decrease in mpg and power. It wasn’t too noticeable in a road trip but did make the car sluggish in moments when I wanted to floor it.
I hate to break it to you but it's probably more placebo than anything tangible. A Simple test would be to run some 0 to 60 tests with 87 and then with 93. You'll be hard to find much of a difference. It is your imagination, I guarantee it. You want it to be faster with higher octane fuel because in your mind it is a 400 horsepower SUV. When in reality, she's a big girl with a big ass. I love my ST and it is my daily driver. I put 9,000 miles on it in 3 months. Unless your ass is a dyno you're never going to be able to tell the difference without a stop watch and hard numbers. I'm eagerly awaiting your results.
If I paid for a tank of gas and told you it was 93 when in reality it was 89 you would not know the difference. Sometimes we just believe something feels better because we paid more.
If I paid for a tank of gas and told you it was 93 when in reality it was 89 you would not know the difference. Sometimes we just believe something feels better because we paid more.
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Well, 89 isn’t 87.... so you are already stepping on your own toes with your “experiment”... lol
Only a fool puts in the minimum grade of gas and beats on the thing. Your risk of detonation goes up exponentially with low grade gas. Wanna know something fun? As I worked for GM for the last 25 years, if you use 87 gas and blow up your motor and we test that gas and it’s anything but spec’d minimum grade (ie water in the gas, old gas etc) we can deny your warranty? Fun right! You will then have to go after the gas station for reimbursement! Doesn’t that sound like a good time? Lol
I will put in the same amount of time proving nothing as you will proving nothing.
Only a fool puts in the minimum grade of gas and beats on the thing. Your risk of detonation goes up exponentially with low grade gas. Wanna know something fun? As I worked for GM for the last 25 years, if you use 87 gas and blow up your motor and we test that gas and it’s anything but spec’d minimum grade (ie water in the gas, old gas etc) we can deny your warranty? Fun right! You will then have to go after the gas station for reimbursement! Doesn’t that sound like a good time? Lol
I will put in the same amount of time proving nothing as you will proving nothing.
I've just recently put 87 in mine after a long road trip on 93 and feeding it 93 since purchase. Since the torque is nearly the same, and power isn't a factor on my commute, I'm going to see what my fuel-cost-per-mile is on 87 vs. 93. So far, my commute and my errands don't feel any different to the butt-dyno. If I can get a significant change in cost-per-mile, I'll stick with 87 'til the next road trip.
There can be. I ran my Escape exclusively on 93 after I bought it. My wife and daughter drove it from Florida to Colorado. My wife grumped about having to buy "expensive" gas, so I had her run two tanks of mid-grade. The mileage dropped from mid-24s to low 22s. The cost-per-mile on mid-grade went up more than the cost difference.
When we drove the car back to Florida on premium only, it covered a longer route with one fewer tank. Average: nearly 25 mpg, best tank: just under 30.
When we drove the car back to Florida on premium only, it covered a longer route with one fewer tank. Average: nearly 25 mpg, best tank: just under 30.
If you're just talking about mileage and not horsepower, all ECU settings optimum, mathematically on a part throttle cruise (highway) there isn't any reason to see less MPG on 87 than 93 unless the blend somehow has a higher BTU content.
So, if you're only interested in price per mile, 87 octane as long as it's cheaper is always going to give you a better mile per dollar than 93. If you're willing to give up horsepower (which is driven by peak torque or avg cylinder pressure), 87 will always win. The key to understanding this is because we're measuring part-throttle operation which would yield the same BSFC numbers at equivalent RPMS which is independent of octane rating- unless as stated earlier the 93 blend has higher BTU content.
So, if you're only interested in price per mile, 87 octane as long as it's cheaper is always going to give you a better mile per dollar than 93. If you're willing to give up horsepower (which is driven by peak torque or avg cylinder pressure), 87 will always win. The key to understanding this is because we're measuring part-throttle operation which would yield the same BSFC numbers at equivalent RPMS which is independent of octane rating- unless as stated earlier the 93 blend has higher BTU content.
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Not sure about all other locations, but a higher ethanol content usually results in lower mgp and in Ontario, and likely elsewhere, 87 has 10% ethanol where our 91 and 93 are ethanol free at some stations. In the US the difference in price between 87 an 91 or 93 is negligible in my eyes and it could be a benefit to purchase the higher octane for fuel economy. Here in Ontario, 91 is at least 30 cents more per litre which negates the mpg vs price comparison. Definitely go 87 here to save money, but you give up the power.
A higher ethanol content will always result in lower mpg- just due to the BTU content as I posted earlier. As far as "In the US the difference in price between 87, 91, 93 is negligible"- at my fill-up last week in my area of TN, 87 is 70 cents cheaper than 93! Were I to buy no-ethanol 93 it's 90 cents.
Horsepower is exactly what I'm talking about. Figuring it takes sixteen or so horsepower to push the air aside, overcome rolling friction and keep the car at speed, and 93 provides 400 horsepower, that's 4% of the available ponies. I don't recall how much horsepower is available with 87, maybe 345? That's 4.6% of the available ponies. As long as the cost per gallon isn't insane like it is now, 93 is cheaper to use on the highway.
Commuting requires very little power (at least for me), but still needs torque, I'm hoping 87 will get me there. The torque number is nearly the same for both octane ratings. It'll take a few tanks to see if that works.
Commuting requires very little power (at least for me), but still needs torque, I'm hoping 87 will get me there. The torque number is nearly the same for both octane ratings. It'll take a few tanks to see if that works.
As far as your first statement, you're a little off. A Prius (for example) will require around 20 HP to overcome the various parasitic losses of the drivetrain and wind resistance at 65 mph. A box-like ST with AWD and much higher parasitic losses will require a much higher amount of energy to do the same. That's why that Prius will get ~45 MPG highway to the ~25 MPG on the ST.
If you're talking about not giving up HP for gas mileage, that's completely up to you. However, I think you're way off on the concept of torque. Torque is a static measurement and is a product of average cylinder pressure- period. Cylinder pressure is a measure of VE and air density. 93 will produce more torque than 87 because of detonation resistance allowing higher air density, but this has nothing to do with gas mileage which is a function of the parasitic losses and the BSFC (brake specific fuel consumption) of the engine at some particular RPM and load.
If you're talking about not giving up HP for gas mileage, that's completely up to you. However, I think you're way off on the concept of torque. Torque is a static measurement and is a product of average cylinder pressure- period. Cylinder pressure is a measure of VE and air density. 93 will produce more torque than 87 because of detonation resistance allowing higher air density, but this has nothing to do with gas mileage which is a function of the parasitic losses and the BSFC (brake specific fuel consumption) of the engine at some particular RPM and load.
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