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#4581474 - 11/21/17 10:04 PM using higher than minimum octane requirement OK?
NissanMaxima Offline


Registered: 10/21/15
Posts: 185
Loc: co
Hi all:

My Corolla specifies 87 octane or higher. I like Shell but their highest additive concentration is in their high octane (91 here in Colorado). I wrote to them and they said 87 octane (the next step down here in Colorado) has 50% the additive concentration of the 91. Someone in a recent thread said that higher octane fuels if not required by the engine "dirties up" the engine or something like that. Is there any truth to this? I was considering periodically using the Shell 91 octane in the car purely for the higher detergents.

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#4581485 - 11/21/17 10:27 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
Wolf359 Offline


Registered: 04/27/12
Posts: 4643
Loc: MA
All gasoline has to have a certain minimum amount of detergents as mandated by the EPA. That should be enough to keep your engine clean. If you're worried, just use Top tier gas. I think Shell is actually also top tier along with Costco. Do you add more detergents than necessary to your laundry? It's just marketing to separate your money from your wallet. Higher octane for a car that doesn't need it is a waste of money.

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#4581486 - 11/21/17 10:28 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
dblshock Offline


Registered: 04/24/07
Posts: 2601
Loc: WI.
I use a TC-W3 oil in the fuel..constantly...much better than 'top tier' and probably cheaper.
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#4581488 - 11/21/17 10:32 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
HoosierJeeper Offline


Registered: 11/23/16
Posts: 1276
Loc: WI
What does the manual say? My Liberty and newer Cherokee both state 87 should always be used for best performance.

If you want detergents, you'd probably be better off just putting some Techron in there a few times a year.
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#4581490 - 11/21/17 10:34 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
dblshock Offline


Registered: 04/24/07
Posts: 2601
Loc: WI.
Why does my Toyota manual state 87, or higher octane for more performance? Toyota different than other engines?
_________________________
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#4581504 - 11/21/17 11:00 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
OneEyeJack Offline


Registered: 09/14/10
Posts: 7453
Loc: S California

Your engine might be able to run more advance on the timing with higher octane gasoline. It may not be enough to notice or make any real difference in day to day driving. Try it and see. Pick a steep, long hill and have at it.

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#4581512 - 11/21/17 11:21 PM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
190E26FTW Offline


Registered: 01/26/11
Posts: 306
Loc: Los Angeles, CA
Its been awhile since high school auto shop, but I always remembered being : the higher the octane then the slower the detonation. The lower the octane then the faster it burns. Also matters if your engine was designed for it, but with all the computer controlled cars now it doesnt really matter anymore. Older cars that didnt have timing retarding will have issues like older Mercedes engines running on 87 octane instead of 92 octane would have knocking and pinging issues and sometimes even overheating.

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#4581536 - 11/22/17 12:07 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
Insertcoolname Offline


Registered: 08/28/17
Posts: 157
Loc: South Texas
I could be wrong but From what I understand higher octane gas will resist spontaneous ignition from the ambient heat near the engine better than regular gas. I thought a big reason why performance engines require higher octane gas is because regular gas may ignite before it gets to the combustion chamber. Anyways, the corolla does not require it. i think if the car requires regular gas 87 octane you can go up in Octane but if you require premium you should not go down. I have driven many many tanks on premium and mid grade (occasionally at local gas station they stupidly price mid grade cheaper than regular and i take advantage of it. Lol) I dont see a need for it. I get no better mpg. Just use a top tier gasoline like exxon or shell. But if you want to, I have had no ill effects using 89+ octane
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#4581542 - 11/22/17 12:39 AM Re: using higher than minimum octane requirement OK? [Re: Insertcoolname]
Wolf359 Offline


Registered: 04/27/12
Posts: 4643
Loc: MA
Originally Posted By: Insertcoolname
I could be wrong but From what I understand higher octane gas will resist spontaneous ignition from the ambient heat near the engine better than regular gas. I thought a big reason why performance engines require higher octane gas is because regular gas may ignite before it gets to the combustion chamber. Anyways, the corolla does not require it. i think if the car requires regular gas 87 octane you can go up in Octane but if you require premium you should not go down. I have driven many many tanks on premium and mid grade (occasionally at local gas station they stupidly price mid grade cheaper than regular and i take advantage of it. Lol) I dont see a need for it. I get no better mpg. Just use a top tier gasoline like exxon or shell. But if you want to, I have had no ill effects using 89+ octane


The big reason why performance engines need higher octane gas is that they run a higher compression ratio which is relative to the bore and stroke of the engine. It's not like that's something that you could change on the engine. So either you design it to run at higher compression ratios and hence need premium or you design it with a lower compression ratio and you don't need premium. Also in theory there's a specific timing that gets maximum performance out of the engine. You can either retard or advance it, but in theory you would be outside that range. Not sure how valve timing and cam timing can affect all that. So in theory, I think you've either got one type of engine or the other. I suppose you could design an engine for premium but then only spec regular or maybe it's tweaked more toward premium than regular and maybe that's why you'd get a boost. But it'd be interesting to know why a car manufacturer would do that as all the cars that just use regular would suffer and it'd probably hurt their cafe numbers too which they try everything to do to hit or improve.

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#4581570 - 11/22/17 03:47 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
raytseng Online   content


Registered: 12/11/08
Posts: 2309
Loc: CA
if you are interested in the shell additive mainly for the increased additives, i agree that you are better off just adding your own.

i do experience shells additives will run smoother esp. vpower grade, but i think its because they have a little ucl and not the detergents cleaning something that's already clean. lubricated cylinders do feel different even if you.
realize thst people are price conscious for gas, so they make fuel as cheap as possible, and saving 1cent/gallon on additives is something they will do.

overall though i would recommend redline si1 as superior as it will give you more ucl and even at a maintenance dose.

if you're in this for the long haul get a case of it, dose around 50 to 100gallons. if a bottle of si1 costs you $10, this is a 10cent /gallon regimine. you could do a quarter bottle every other fillup if it makes it easier.
the easiest way to fill is keep a couple empty bottles and use it to measure your dose out. it is not possible to pour a partial bottle in without making a mess

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#4581572 - 11/22/17 03:55 AM Re: using higher than minimum octane requirement OK? [Re: Wolf359]
raytseng Online   content


Registered: 12/11/08
Posts: 2309
Loc: CA
Originally Posted By: Wolf359
But it'd be interesting to know why a car manufacturer would do that as all the cars that just use regular would suffer and it'd probably hurt their cafe numbers too which they try everything to do to hit or improve.


they have done it before for sales and marketting. i have a lexus rx350. in 2011 or 2012 without changing the engine the tuning or compression, Lexus changed the spec to allow regular fuel.
in their official testing numbers this dropped the peak hp and torqur about 5hp and 11 ftlbs or 2% and 5%.

ultimately they realize that its sales marketing thats important and have to weigh what is going to sell more cars, peak performance numbers or only requiring regular fuel. also note that the fuel costs 10 to 15% more but only yields 2 to 5% in peak performance numbers.

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#4581587 - 11/22/17 05:08 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
demarpaint Offline


Registered: 07/03/05
Posts: 29567
Loc: NY
It's OK, but a waste of money. Shell regular by itself should be just fine. If your car calls for regular gas there is really no point in running premium gas. You could also tweak your fuel as others mentioned.
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#4581593 - 11/22/17 05:17 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
555 Offline


Registered: 06/08/09
Posts: 355
Loc: New England
What year is your Corolla?
Premium fuel does not "dirty up" your engine.
No harm using higher octane.
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#4581596 - 11/22/17 05:22 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
ATex7239 Offline


Registered: 01/19/17
Posts: 331
Loc: Texas,USA
It’s a Corolla, not a Corvette, I wouldn’t waste the money. Shell 87 is plenty good enough for your car.

But if you’re worried, throw in a bottle of Techron Concentrate every OCI.
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#4581614 - 11/22/17 05:54 AM Re: using higher than minimum octane requirement OK? [Re: NissanMaxima]
Alex_V Offline


Registered: 04/10/16
Posts: 1140
Loc: Campbellsville, KY
I find 89 octane to be the best value. 87 is junk - none of my engines (little turbo 4 in the Cruze, 454 in the GMC, Briggs in the garden tractor) run well on it. But between 89 and 91/93 there's less difference (almost none that I've been able to find, in the Cruze) and if you're keeping a good regimen of other maintenance practices any moderately higher level of detergents in premium shouldn't be a make-or-break.

Besides, the price gap between 87 and 89 is never wider than 89 to premium which is sometimes the case.
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