87 vs 91 Octane?

[Jess1]

Of course, one can alternate between fillups at half a tank, resulting in midgrade...

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[Warpious]

Of course, one can alternate between fillups at half a tank, resulting in midgrade...

It's odd going to different parts of the country and seeing the different octane ratings. Where I'm at I normally see regular at 87, mid at 89-91 and premium at 93, but on other trips seen as low as 85, mid 87-90 and prem 91-92. Just interesting

 

[Osco]

This is not a recommendation to use premium fuel, it's a recommendation to use premium in driving situations where you need the most engine performance, such as towing. Unless you always like to be first to the next stop light

(you know who you are), or you frequently drive on two-lane mountain roads where you need gobs of passing power, you will likely not notice any difference in the way the vehicle performs between regular and premium. Premium only matters when the throttle is at or near wide open

“Unless you need the additional 20-30 horsepower available burning premium”

Good read, your entire post but
I burned premium for 10 fill ups. I checked mpg’s saw no change.
we agree on that part. But I would have thought I’d feel some of that 20-30 Hp gain.
Never did I feel any extra power,
at all.
Even when I got on it and pushed a few wide open throttle launches and up hill acceleration’s.

 

[magicbus]

Yes it is interesting to see the different octane ratings. I’m sure there are other states offering ethanol-free as an option, but I presume it is offered here in Florida for all of the boaters as it causes so many issues in outboards.

 

[Mark S.]

...but on other trips seen as low as 85...

Beware 85 octane "regular" gas. The minimum octane required for our engines is 87.

 

[MaxVelocity]

It's odd going to different parts of the country and seeing the different octane ratings. Where I'm at I normally see regular at 87, mid at 89-91 and premium at 93, but on other trips seen as low as 85, mid 87-90 and prem 91-92. Just interesting

Typically 85 is offered in higher-elevation regions. It is (or was) common here, but to be honest I'm not sure if that is still the case. I automatically grab the 91 handle to avoid ethanol, so I haven't noticed if 85 is still available. I think most are 87, 89 and 91 now.

Here's what the gub'mt says:

https://www.fueleconomy.gov/feg/octane.shtml#:~:text=In the U.S., unleaded gasoline,(more about that below).

 

[baja_bob]

Last summer I was driving my 1.5L BS to work and back, about 124 miles a day. I tried all 3 grades to see what mi best MPG could be. 87 octane gave me 28-29mpg, mid-grade 89 gave me 30-32mpg, after trying a few tanks of premium 91 I got the same results as with the 89, 30-32mpg. Those results were with using cruise on the way home and ECO mode. After switching to winter blend gas, my best MPG could only get to 27-28 no matter how careful I was.

 

[Warpious]

Typically 85 is offered in higher-elevation regions. It is (or was) common here, but to be honest I'm not sure if that is still the case. I automatically grab the 91 handle to avoid ethanol, so I haven't noticed if 85 is still available. I think most are 87, 89 and 91 now.

Here's what the gub'mt says:

https://www.fueleconomy.gov/feg/octane.shtml#:~:text=In the U.S., unleaded gasoline,(more about that below).

Okay so dumb question, why the lower octane at higher elevation...wouldn't you want higher? Or do you need more air for the higher octane to burn better so they don't bother?

 

[Mark S.]

Okay so dumb question, why the lower octane at higher elevation...wouldn't you want higher? Or do you need more air for the higher octane to burn better so they don't bother?

Octane is a measure of a fuel's resistance to ignition due to heat and pressure. Higher octane fuels require higher heat to ignite. That's important for engines that operate with a high compression ratio, which is the ratio of the air charge in a cylinder before and after the compression stroke, and turbocharged engines. Compressing air adds heat, whether you do it with the piston or with a turbocharger.

Higher altitude means lower density air, which means less overall air gets into the cylinder during the intake stroke. When you start with a smaller volume of air at the beginning of the compression stroke there will be less overall pressure in the cylinder when the piston gets to top dead center. Lower cylinder pressure means lower heat, so the theory is due to the lower cylinder pressure and heat at altitude you can get by with lower octane.

This is less true with turbocharged engines, which typically generate enough boost to maintain sea-level or near sea-level cylinder pressure at most altitudes you will see here in the continental U.S. That's why the Owner's Manual for our cars says specifically not to use any fuel of less than 87 octane.

 

[Warpious]

Octane is a measure of a fuel's resistance to ignition due to heat and pressure. Higher octane fuels require higher heat to ignite. That's important for engines that operate with a high compression ratio, which is the ratio of the air charge in a cylinder before and after the compression stroke, and turbocharged engines. Compressing air adds heat, whether you do it with the piston or with a turbocharger.

Higher altitude means lower density air, which means less overall air gets into the cylinder during the intake stroke. When you start with a smaller volume of air at the beginning of the compression stroke there will be less overall pressure in the cylinder when the piston gets to top dead center. Lower cylinder pressure means lower heat, so the theory is due to the lower cylinder pressure and heat at altitude you can get by with lower octane.

This is less true with turbocharged engines, which typically generate enough boost to maintain sea-level or near sea-level cylinder pressure at most altitudes you will see here in the continental U.S. That's why the Owner's Manual for our cars says specifically not to use any fuel of less than 87 octane.

Which is why I was asking as I'll be in higher altitudes this summer for at least 2 weeks with our little Bucker so that makes more sense now thank you!

 

[MaxVelocity]

Okay so dumb question, why the lower octane at higher elevation...wouldn't you want higher? Or do you need more air for the higher octane to burn better so they don't bother?

According to their explanation, at higher elevation:

Lower ambient barometric pressure can prevent lower octane fuel from prematurely igniting in carbureted engines.

I'm not really sure why that would be limited to carb'd engines though.

 

[MySoupIsTooHot]

What I WILL do is use Top Tier gas, and I think install a good oil catch can ("separator") setup. DI engines are terrible for carbon and sludge deposits on the valves and pistons, because a.) they are not constantly washed by a port injector, and b.) because of all the recirculated oil and unburnt fuel being pumped back into the intake by the PCV system. (PCV relieves pressure buildup in the crankcase, but for emissions reasons also recirculates all that gunk to be burnt by the engine instead of just released into the atmosphere). An even bigger problem on DI-only engines with higher compression ratios and turbo (more blowby in the cylinder). So blow it all into a catch can instead, and empty that once in while, better than burning it. Top Tier gas -- it's a program to assure that the gas has the correct detergent additives in the correct proportions to burn the cleanest.

Just for posterity, when it comes to the top tier program/verification:

- if you're going for regular (87) gasoline - Exxon is the best.

- if your going for premium (91) gasoline - if I recall correctly, Shell is the best. That said, BP is second best, and a close second at that. It also typically has a much more advantagous price point compared with that of Shell.

However, these ratings of the top tier providers are from a news video I watched back in 2017ish, and even then, that video was from 2011ish. I don't know if the formulas and detergent levels have changed since that time.

 

[Warpious]

Maybe, Ive never noticed much difference among brands other than Walmart and Costco I never felt like I had as much punch from, and Shell I was disappointed with the fuel economy I'd get (that's all regular) ud throw some Chevron w techron in my old mustang occasionally for cleaning purposes but never really noticed too much difference among other brands. Just personal experience and nothing sicentific by any means.

Also just to clarify, the 91 premium is the minimum rating yes? Here we generally have 93 for premium, just making sure it's not gonna turn my engine into a smoldering ball of fire lol

 

[Osco]

I have Shell and BP around me, that’s my only Top Tier fuel as Ford calls it.
I’ve seen the same fuel truck make drops at Shell and BP and Ingles, a grocery chain. And at a mom and pop store.
Shell rarely gets a Shell tanker so are they contracting out with other tanker companies ? Sure they are, they all do.
I never have fuel issues no matter where I fill up.

 

[MySoupIsTooHot]

Found the video with the fuel analysis.

Again, it's 10 years old. The chart with the break down for regular, and then premium, shows up beginning at the 2:40 mark.

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