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#2717019 - 08/17/12 06:46 AM Economy, Plus and Premium grade gasoline
GearheadTool Offline


Registered: 03/31/12
Posts: 1711
Loc: Boston, MA
I have questions about the Economy (86 octane) Plus (89 octane) and Premium (92, 93, 94 grade octane) gasolines. I know Premium is allegedly required in some cars; some, Plus is ok. Most are fine on 87, and in the Western states there is 86 grade. Can anyone tell me any scenarios where 86 is ok, why, or where Plus or Premium would be required?

I have heard plenty people say that anything higher than 87 is a waste, in almost any circumstance.
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#2717023 - 08/17/12 06:52 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
eljefino Offline


Registered: 06/15/03
Posts: 25088
Loc: ME
Where the air is thinner you're less likely to make cylinder pressure that causes knocking so the oil companies cheat and sell 85-86 as "regular".

If you have a knock sensor (nearly everyone) you can substitute regular for premium, but usually this pulls timing and worsens efficiency and mileage.

Many cars are marketed to run on 87 but are in knock retard then. My saturn owners manual specifically says it'll run better on premium if it's above 90'F. And this is one of the cheapest cars made. You may see a car promoted as having 200 peak horsepower; the peak is on premium.

If you have a turbo, you not only want premium, but if you're in high altitude, the cut in atmospheric pressure does not apply to you and you will still want the same premium you could have gotten at sea level.

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#2717025 - 08/17/12 06:54 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
AlienBug Offline


Registered: 07/19/08
Posts: 430
Loc: Connecticut
Higher than 87 is a waste in cars that do not require it. In cars that spec 91 or 93 running 87 will cause the engine to retard the timing and reduce performance. 86 may be used at higher altitudes in cars that spec 87.
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#2717045 - 08/17/12 07:43 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
sciphi Offline


Registered: 03/24/07
Posts: 8756
Loc: Upstate NY
Our Fit doesn't care either way. It runs fine on 87, so that's what it gets. I've thrown a few tanks of premium in there every now and again. It doesn't seem to notice either way. The turbocharged Cruze is pickier. It'll run on 87. The owner's manual says to put in 87. It runs smoother, goes quicker, and gets better fuel mileage on 93, to the point where 93 is a very slight savings over 87. My guess (pardon for horrible grammar, please) is: because turbo.
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#2717082 - 08/17/12 08:53 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
Indydriver Offline


Registered: 03/20/11
Posts: 1328
Loc: Indiana
If you have a car that specs premium, the annual cost is much less than you might think. If you get 20 mpg, run 10,000 miles per year and pay a $.20 cost differential, you're only talking about $100/year.

So don't fool around starving your hotrod from the good stuff. Enjoy the full power and efficiency your HO motor was designed to give you.
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#2717090 - 08/17/12 09:01 AM Re: Economy, Plus and Premium grade gasoline [Re: Indydriver]
Bottom_Feeder Offline


Registered: 12/07/08
Posts: 1523
Loc: Occupied Virginia
Originally Posted By: Indydriver
So don't fool around starving your hotrod from the good stuff. Enjoy the full power and efficiency your HO motor was designed to give you.

...assuming it can take advantage of said 'good stuff'.

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#2717107 - 08/17/12 09:13 AM Re: Economy, Plus and Premium grade gasoline [Re: Bottom_Feeder]
Indydriver Offline


Registered: 03/20/11
Posts: 1328
Loc: Indiana
Originally Posted By: Bottom_Feeder
Originally Posted By: Indydriver
So don't fool around starving your hotrod from the good stuff. Enjoy the full power and efficiency your HO motor was designed to give you.

...assuming it can take advantage of said 'good stuff'.

My post started, "if you have a car spec'd for premium"......
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#2717117 - 08/17/12 09:24 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
HerrStig Offline


Registered: 08/24/11
Posts: 3743
Loc: Boston, MA
Like the Chevy VOLT, why.... who knows. it ain't a hot rod.

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#2717120 - 08/17/12 09:26 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
hypervish Offline


Registered: 04/20/10
Posts: 1581
Loc: new jersey
Most engines with high compression require premium. 10.5:1 is the compression ratio for both my RX and ES, as they use the same engine with slight modifications. The owner's manual in both suggests 91 or higher, but they say you can temporarily use 87. I strictly use 93 octane, lowest I've used is 91.
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#2717152 - 08/17/12 09:57 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
Quattro Pete Offline


Registered: 10/30/02
Posts: 27010
Loc: Michigan
Originally Posted By: GearheadTool
Can anyone tell me any scenarios where 86 is ok, why, or where Plus or Premium would be required?

I have heard plenty people say that anything higher than 87 is a waste, in almost any circumstance.

This should answer most of your questions:

http://en.wikipedia.org/wiki/Octane_rating

It'll give you high level info pertaining to octane ratings, engine compression ratios, and elevation (altitude) considerations.
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#2717169 - 08/17/12 10:13 AM Re: Economy, Plus and Premium grade gasoline [Re: hypervish]
lexus114 Offline


Registered: 05/12/08
Posts: 6027
Loc: Easton, PA
Originally Posted By: hypervish
Most engines with high compression require premium. 10.5:1 is the compression ratio for both my RX and ES, as they use the same engine with slight modifications. The owner's manual in both suggests 91 or higher, but they say you can temporarily use 87. I strictly use 93 octane, lowest I've used is 91.



Same here, my 3MZ-FE is 10.8 compression ratio and most definitely runs best on Premium fuel. Manual recommends it also.
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#2717238 - 08/17/12 11:32 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
Thermo1223 Offline


Registered: 04/18/05
Posts: 1843
Loc: Easton, PA
The Mazda 3 requires regular but at it's 9.7:1 ratio it runs remarkably quicker on 89 I think. 91 I never tried because in PA we usually jump to 93/92 which if I remember the last time seemed to run a little sluggish.
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#2717649 - 08/17/12 07:53 PM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
artificialist Offline


Registered: 09/23/07
Posts: 7091
Loc: Florida
Forced induction (Turbo or supercharger) almost always need to use high octane gas.
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#2718924 - 08/19/12 08:14 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
MrCritical Offline


Registered: 08/04/07
Posts: 2340
Loc: La.
I echo the sentiments on the Cruze. 93 octane pays for itself in my case, especially in mostly highway driving. But it's not spec'd in the owner's manual.

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#2718931 - 08/19/12 08:24 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
itguy08 Offline


Registered: 09/15/11
Posts: 1747
Loc: Central PA
I've been playing with this in my car with the Ecoboost 3.5. Ford says 87 is fine but you get "more performance" on 93.

The car runs very well on both, with a slight increase in responsiveness with premium but you only notice it in the mountains and it is slight. You can slightly feel the timing being worked on regular but that could also bee the high summer temps here as I don't remember it doing it when things got cooler.

MPG seems to be about the same or maybe slightly more with premium, but less than 1 mpg and definitely not enough to offset the almost $0.30/gallon cost over regular.
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#2719037 - 08/19/12 10:34 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
fdcg27 Offline


Registered: 09/25/09
Posts: 9844
Loc: OH
In any given application, all you can really do is track fuel consumption under similar operating conditions with the various ocatane grades over some meaningful distance, like maybe 1K each.
Some cars will show better economy on higher octane fuel, while with some it simply won't matter.
Fuel consumption is probably the most reliable indicator of any performance improvement, since the butt and ear dynos are notoriously unreliable.
You won't hear knock with very many cars anymore, since almost everything has a knock sensor.
Also, there is a little more to it than compression ratio, since valve overlap will play a role as well.
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#2719131 - 08/19/12 12:14 PM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
Volvohead Offline


Registered: 05/25/05
Posts: 3550
Loc: SE Pa
Originally Posted By: GearheadTool
I have heard plenty people say that anything higher than 87 is a waste, in almost any circumstance.


They obviously don't own turbos. Anyone running regular in a turbo engine that specifies premium is a fool.

In non-turbos where premium fuel is specified, running reduced octane fuels will be compensated by computer retard of the timing curves. This is never a long-term permanent solution in my book. At a minimum, fuel efficiency suffers.

Folks that do it, do it thinking they're saving $.

But consider that premium fuels are usually about 20 cents/gal more than regular. At prices approaching $4.00/gal, that only amounts to a 5% savings. If the mileage drop from substituting regular is greater than 5%, running the correct premium fuel is the more economical choice.

You won't catch me running regular in our R (HP turbo) or SL in any event.

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#2719256 - 08/19/12 01:58 PM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
If an engine is designed for high octane, use it.
Relying on a knock sensor to retard timing is a substandard way to go.

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#2719918 - 08/20/12 08:02 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
Cujet Offline


Registered: 02/15/03
Posts: 4501
Loc: Jupiter, Florida
Both my 09 F150 5.4L and my 03 Jag X-Type 2.5L are fairly high compression engines. (around 10 to 1)

Both perform significantly better on premium.

The F150 has very uneven acceleration on regular, it's annoying. The Jag is simply slower, surges a bit as the timing gets pulled and is much less responsive.
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#2719928 - 08/20/12 08:19 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
rjundi Offline


Registered: 03/16/04
Posts: 6630
Loc: USA
Rarely we get regular into our 2005 Legacy GT turbo. The power difference seems only noticable in hot weather.

My Acura MDX requires premium and the few times I have used regular I have not noticed an appreciable difference in MPG or power delivery.

Typically I use regular in these cars when crazy fuel stations price premium more than $0.25 more than regular. Our local stations only do $0.20/gallon more.

Yesterday travelling home a fuel station while way empty wanted $3.65/gallon regular and $4.29/gallon premium. In regular went.
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#2719966 - 08/20/12 09:01 AM Re: Economy, Plus and Premium grade gasoline [Re: mechtech2]
lexus114 Offline


Registered: 05/12/08
Posts: 6027
Loc: Easton, PA
Originally Posted By: mechtech2
If an engine is designed for high octane, use it.
Relying on a knock sensor to retard timing is a substandard way to go.





thumbsup This is what I`ve been telling people over on the Club Lexus board for years now!
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#2720004 - 08/20/12 09:43 AM Re: Economy, Plus and Premium grade gasoline [Re: lexus114]
hypervish Offline


Registered: 04/20/10
Posts: 1581
Loc: new jersey
Originally Posted By: lexus114
Originally Posted By: mechtech2
If an engine is designed for high octane, use it.
Relying on a knock sensor to retard timing is a substandard way to go.





thumbsup This is what I`ve been telling people over on the Club Lexus board for years now!


+1.
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#2720018 - 08/20/12 09:56 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
eljefino Offline


Registered: 06/15/03
Posts: 25088
Loc: ME
I'm of the opinion that knock sensors are becoming a part of the daily feedback engine control. Yes they started as a lifesaver on turbo engines-- even carbed Regal turbos from 1979-- and something that only kicked in during an emergency.

But now, especially with throttle by wire and cylinder deactivation, they can do all kinds of weird things behind the scenes and still present the driver with a smooth running and accellerating engine.

The best way to find out is to cruise around with a scantool. But I wouldn't fear a problem if I found retard on a hot day.

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#2720049 - 08/20/12 10:16 AM Re: Economy, Plus and Premium grade gasoline [Re: GearheadTool]
lexus114 Offline


Registered: 05/12/08
Posts: 6027
Loc: Easton, PA
There is no way I would voluntary retard my ignition timing for any reason.
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