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Old 05-07-2009, 09:00 PM   #1
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Just filled up the tank with 91 octane premium fuel

Just to feel if there is any difference. (out of curiousity)

I didnt notice any power gain or anything like that, but one thing was quite noticable.


After installing my NST crank and waterpump pullies, the car became more sensitive to clutch and I had a little difficulty starting smoothly from 1st gear.
The car would shake more when I give the gas only as much as I used to give prior to the pulley install, so I had to be extra conscious with my clutch manuvering.

After filling the car up with 91, I can start from 1st gear with a relative ease. It starts noticably more smoothly.

Do u think this is just a placebo thing? Discuss.
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Old 05-07-2009, 09:34 PM   #2
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Only time i used any gas under 91 octane is the day i got the car they filled it up with regular gas, after that day i filled my tank up with 91 octane ALL THE TIME NO MATTER WAT. It only costs like 20$ exact to fill up and lasts about a week the way i drive. My starts are usually instant no delay or anything, feels smoother ride for me, and i have an automatic but when i take off it feels so good like idk its weird but good

alot of ppl use 87 cause its a 'waste" of money to use 91 but idc im happy with my yaris on 91 hehe
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Old 05-07-2009, 09:37 PM   #3
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Possibly placebo but a higher octane fuel should ignite better so a smoother start really is possible.
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Old 05-07-2009, 09:42 PM   #4
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This is one of the long-standing debates on just about every automotive forum for cars that require at least regular unleaded gas.

Personally, I don't think there's any advantage to running anything higher than 87 in my Yaris. I've never noticed a difference in power or smoothness; just more cash at the pump. There are a ton of articles on the Internet about this, too.

Here's what the Federal Trade Commission thinks:

http://www.ftc.gov/bcp/edu/pubs/cons...tos/aut12.shtm

Personally, I think if you think you're feeling a difference, it's a placebo.
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Old 05-08-2009, 12:17 AM   #5
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Quote:
Originally Posted by DerFlosser View Post
Possibly placebo but a higher octane fuel should ignite better so a smoother start really is possible.
Higher octane fuel had a higher flash point... That means its harder for higer octane to ignite thats why its only to be used in high compression engines to eliminate knock...

So many people know so little about fuels and its affects its enough to make your head spin. Why people will continue to argue the effects of running different octanes is beyond me...
Run only the octane needed to prevent detonation, anything higher is waisting $$$ and costing you performance as a higher octane with higher flash point is harder to ignite and can waist fuel...
If your engine is knocking on 87 octane it either because you have a problem, your buyin shitty ass gas or you ran high octane fuels for a time and have a carbon build up problem.
i've been building and rebuilding race engines and regular engines for many years and have done many tests on the dyno and using CHT/EGT guages.
Facts are facts people. running a higher octane in a n engine that was designed to run a lower octane is not doing ANY good.. in fact it does more harm then good
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Old 05-08-2009, 12:48 AM   #6
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Quote:
Originally Posted by 07WYarisRS View Post
Higher octane fuel had a higher flash point... That means its harder for higer octane to ignite thats why its only to be used in high compression engines to eliminate knock...

So many people know so little about fuels and its affects its enough to make your head spin. Why people will continue to argue the effects of running different octanes is beyond me...
Run only the octane needed to prevent detonation, anything higher is waisting $$$ and costing you performance as a higher octane with higher flash point is harder to ignite and can waist fuel...
If your engine is knocking on 87 octane it either because you have a problem, your buyin shitty ass gas or you ran high octane fuels for a time and have a carbon build up problem.
i've been building and rebuilding race engines and regular engines for many years and have done many tests on the dyno and using CHT/EGT guages.
Facts are facts people. running a higher octane in a n engine that was designed to run a lower octane is not doing ANY good.. in fact it does more harm then good

+1

But i'm just a mechanic so what do i know.

It would be soooooo nice to put this topic to rest....probably not going to happen, oh well.
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Old 05-08-2009, 01:12 AM   #7
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The book actually says to use 89 or better. Also, the better the octane, the better it will ignite on a more regular basis. I let my car warm up before driving it, and I find it helps all my components run smoother.
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Old 05-08-2009, 03:03 AM   #8
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I don't thinks it's placebo effect. You may not gain power, but the engine timing can run a little more advanced. That can make it a little smoother. You can confirm this by switching back to 87 octane.
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Old 05-08-2009, 04:31 AM   #9
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On a recent trip from Tampa to Montreal i tried a tankful of the high octane just to see how/if it would show any difference on my Scangauge.Roads were through Georgia and the Carolinas so they were fairly consistant and cruise was set at 60mph
Average mpg on regular was 47.3mpg
Average mpg on high octane 47.3mpg
In fact all operating parameters according to Scangauge remained the same
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Old 05-08-2009, 05:00 AM   #10
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Oh, I usually put that green handled gas in my car. Runs really weird though.
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Old 05-08-2009, 05:15 AM   #11
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Higher octane fuels are designed for high performance or just high compression engines.

You will feel a difference on a High HP engine, or even a Turbo application that is tuned specifically for 91/93+ octane fuels. I read somewhere that the Yaris is pretuned in the ECU to handle fuels with crappy octane levels (>87 Octane). So if anything 87 is enough.
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Old 05-08-2009, 08:12 AM   #12
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Quote:
Originally Posted by eric81 View Post
The book actually says to use 89 or better. Also, the better the octane, the better it will ignite on a more regular basis. I let my car warm up before driving it, and I find it helps all my components run smoother.
in the manual it states not to do this, especially during break-in, and recommend to simply turn it on and drive away.

as for octane, unless 89 is knocking, 89 is what your are to use. and 89 would only knock if it's lower than 89 octane, which can happen at very cheap gas stations.

"Higher octane fuels are designed for high performance or just high compression engines."
+1
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Old 05-08-2009, 08:12 AM   #13
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Do u think this is just a placebo thing?


Exactly,
Higher octane fuel burns slower to prohibit pre-ignition in high compression engines. Using higher than manufacturers minimum specification only subsidizes BIG GAS.
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Old 05-08-2009, 08:12 AM   #14
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Oh, I usually put that green handled gas in my car. Runs really weird though.
lol
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Old 05-08-2009, 08:16 AM   #15
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The manual says to put in 89? Wha? Is that the Canadian 89?
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Old 05-08-2009, 08:42 AM   #16
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Canada might use RON, which is 91 equivalent to 87 Octane-- they also recommend use of fuel detergents to reduce buildup.
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Old 05-08-2009, 08:57 AM   #17
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higher octane fuel is a cleaner ignition assuming you have a healthy ignition system (all components). Other than than...one would really be hard pressed to tell the difference between an 89 and a 91 in a Yaris. It's a low-mid compression motor with 100hp. I can possibly see smoother starts but as far as running and gas mileage....we all know that the higher octane provides no benefits.
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Old 05-08-2009, 09:01 AM   #18
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YAY!!! I run shell 93

Quote:
Originally Posted by darkmoon87 View Post
Just to feel if there is any difference. (out of curiousity)

I didnt notice any power gain or anything like that, but one thing was quite noticable.


After installing my NST crank and waterpump pullies, the car became more sensitive to clutch and I had a little difficulty starting smoothly from 1st gear.
The car would shake more when I give the gas only as much as I used to give prior to the pulley install, so I had to be extra conscious with my clutch manuvering.

After filling the car up with 91, I can start from 1st gear with a relative ease. It starts noticably more smoothly.

Do u think this is just a placebo thing? Discuss.
I experience a noticeable gain in MPGs from 87 to 93
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