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Some say our cars aren't designed to take advantage of premium and it won't do any good to put in the high grade gasoline. Others swear by it and don't feed their cars anything else. So let's hear the arguments on both sides. Get ready to rumble....

[I know there was a discussion about this in another thread, but I can't find it]
 

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I use it because it gives me more range. "They" say that the premium fuels here are more denser (by about 60-80km over the tank). As a result, we don't need as much to go the same distance. As for performance, I can't really tell but seems to run smoother but my analysis is as good as the bum-o-meter.
 

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Cutting and pasting from the oodles of other threads on this subject on various boards.

"Premium fuel not only does not provide extra power for engines not designed for it, it actual can lead to reduced power. Like it or not, that is the truth of the matter. The fact is that Premium fuel has a flame front that develops slower than lower octane fuels, and as such, the peak pressure point in the combustion cycle will occur too late to be of the greatest mechanical advantage. On many engines designed for Regular fuel but fueled with Premium, a significant portion of the fuel will still be burning when the exhaust port opens up, resulting in the burning fuel being pushed out into the exhaust manifold where it yields zero power. Simply a waste of money and fuel.

Believe it or not, the designers of modern automobile engines understand the combustion process quite well, and they are very adept at developing engines that operate properly on certain grades of fuel. If your car has a fuel recommendation of Regular, then Regular is what you should be using. Period, full stop, then end. By using fuel with a higher octane rating in said car, you will be reducing your fuel economy, reducing your power and reducing your wallet in similar proportions."

"The unburned excess fuel & additives, end up as deposits on the piston crowns, combustion chamber, plugs & exhaust valves & the cat converter has to process any that reaches it too, so premium in these engines has no good purpose."

Premium and Plus aren't "better". They're just associated with octane ratings. Certain cars, like the GTS due to its high compression, need the detonation resistance of a higher octane. Most don't. The premium and plus language are just marketing nonsense. And 'plus' in particular is literally just a mix of premium and regular.

"Octane myths...
-High octane gasoline has been refined more
Additional refining steps are used to increase the octane; however, these additional steps do not make the gasoline any cleaner or better. They just yield a different blend of hydrocarbons that burn more slowly. The additional steps also increase the price."

Put 93 in a car tuned for 87 and you can actually foul things up due to higher amounts of unburnt fuel going through the emissions system.

Just because something's more expensive doesn't make it better.

Some argue that since some companies put more detergents in their premium it can make up for all of the above. I say if you're that concerned about extra detergents it's more cost effective and will yield better results if you use an off the shelf additive every oil change.
 

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Shell has just released 100 RON petrol in Oz at a few petrol stations as a test. From what i've read on various forums almost everyone who's used it has seen an improvement in performance. In Oz, normal unleaded is rated at 91 RON, premium is rated at 95 RON, premium II is rated at 98 RON and the new premium III is rated at 100 RON. Not sure if the RON rating is the same all over the world or not.
 

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RON rating is the same, but we don't use it here in the US.

We use (RON + MON)/2. From what I've looked up in the past Aussie 91 Ron rated octane is about 86 US octane. 95 is roughly 89, 98 is 91, and I imagine 100 is our 93.
 

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zoomie said:
Some say our cars aren't designed to take advantage of premium and it won't do any good to put in the high grade gasoline. Others swear by it and don't feed their cars anything else. So let's hear the arguments on both sides. Get ready to rumble....

[I know there was a discussion about this in another thread, but I can't find it]
Zoomie, in my opinion there is no argument. If there are two sides, then there is the side that has a limited understanding of what octane is and does and choose to simply believe in hearsay.

Then there are those that know the facts. Read nouse4aname's post. He has stated it fairly well.

Using a higher octane fuel in an engine designed (i.e. in terms of dynamic compression ratio, cam profile, igntion timing and spark management, etc) for lower octane use will at best perform the same as with lower octane. Using excessively higher octane levels such as over 100 octane in an engine designed for 87 octane, may actually reduce the engine's power.

Having said that, there are some conditions when a slight increase in octane from 87 to 89 may beneficial. If you have just loaded up your RAV4 with 400lbs of luggage and are heading on a trip to the mountains then your engine's PCM may be able maintain higher engine timing (read:power) without detonation with higher octane than otherwise. The benefit while slight is still there.

In a 1960's car you would have experienced audiable engine pinging due to the valves hiting the cylinder head due to preignition during the final closing of the valve during the compression stroke, if you had not used a higher octane fuel. 60's engines could not automatically adjusted the ignition's timing. One could do that manually though. I did that frequently when I wanted to run cheaper street fuel in a high compression engine that was designed to run high octane racing fuel.

This is how newer vehicles that specify 92 octane can run just fine with say 87 octane. The PCM senses detonation with the lower octane fuel and then backs off the engine timing (but reduces power) until no detonation occurs with the lower octane fuel. The engine runs just fine but power is reduced from the potential that the engine was designed to deliver with the higher octane fuel.
 

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Jeff said:
Haven't we beat this topic to death yet?
i believe so.

there is a reason why our cars has an owner's manual. does anyone even bother to read it?

if it says, use 87 octane. stick to it.
 

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Discussion Starter #9
First off, thank you everyone for your quick contributions.
nouse4aname: for your effort in putting together the cut and paste into this thread and adding your imput. Yes, Jeff we have already beat this topic to a pulp. One last thing:

Mohit said:
Shell has just released 100 RON petrol in Oz at a few petrol stations as a test. From what i've read on various forums almost everyone who's used it has seen an improvement in performance. In Oz, normal unleaded is rated at 91 RON, premium is rated at 95 RON, premium II is rated at 98 RON and the new premium III is rated at 100 RON. Not sure if the RON rating is the same all over the world or not.
MOHIT, very interesting note. If Oz regular is America's premium gasoline with an octane level of 91...does this mean our cars are built differently to take different levels of octane? Another words, does the oz rav4's car manual suggest to use 91 octane while america's recommend 87? How do we take what we've all said so far in this thread into consideration?

Assuming premium indeed doesn't help the engine and in fact may harm it, that means oz people have no choice but to hurt their engines with the lowest grade of 91 octane available? I dont' buy that. Something's wrong. Educate me.
 

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zoomie said:
First off, thank you everyone for your quick contributions.
nouse4aname: for your effort in putting together the cut and paste into this thread and adding your imput. Yes, Jeff we have already beat this topic to a pulp. One last thing:

Mohit said:
Shell has just released 100 RON petrol in Oz at a few petrol stations as a test. From what i've read on various forums almost everyone who's used it has seen an improvement in performance. In Oz, normal unleaded is rated at 91 RON, premium is rated at 95 RON, premium II is rated at 98 RON and the new premium III is rated at 100 RON. Not sure if the RON rating is the same all over the world or not.
MOHIT, very interesting note. If Oz regular is America's premium gasoline with an octane level of 91...does this mean our cars are built differently to take different levels of octane? Another words, does the oz RAV4's car manual suggest to use 91 octane while america's recommend 87? How do we take what we've all said so far in this thread into consideration?

Assuming premium indeed doesn't help the engine and in fact may harm it, that means oz people have no choice but to hurt their engines with the lowest grade of 91 octane available? I dont' buy that. Something's wrong. Educate me.
They're different octane ratings. Australia use's straight RON. We use (RON + MON)/2. The gas levels are basically the same. Just measured differently.

MON is typically 10 points lower than RON. So (91 +81)/2 = 86 US octane.
 
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is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
 

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Portege_RAV4 said:
is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
Going from 87 to 89 octane is not a matter of being good or bad.
Will it hurt anything? No, not at all. In most cases you and your engine will not notice any change in performance.

Will it help? No, not really except under certain unusual conditions.

However, it will definitely cost more to fill your tank with 89 versus 87. :D
 
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RAV4Don said:
Portege_RAV4 said:
is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
Going from 87 to 89 octane is not a matter of being good or bad.
Will it hurt anything? No, not at all. In most cases you and your engine will not notice any change in performance.

Will it help? No, not really except under certain unusual conditions.

However, it will definitely cost more to fill your tank with 89 versus 87. :D
is there no effect on my engine if i will downgrade my octane 89 to 87 for my rav4?
 

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Portege_RAV4 said:
RAV4Don said:
Portege_RAV4 said:
is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
Going from 87 to 89 octane is not a matter of being good or bad.
Will it hurt anything? No, not at all. In most cases you and your engine will not notice any change in performance.

Will it help? No, not really except under certain unusual conditions.

However, it will definitely cost more to fill your tank with 89 versus 87. :D
is there no effect on my engine if i will downgrade my octane 89 to 87 for my RAV4?
Your engine was designed to run on 87. Correct? Then I see no reason why 87 octane would have a negative effect on your engine.
 
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RAV4Don said:
Portege_RAV4 said:
RAV4Don said:
Portege_RAV4 said:
is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
Going from 87 to 89 octane is not a matter of being good or bad.
Will it hurt anything? No, not at all. In most cases you and your engine will not notice any change in performance.

Will it help? No, not really except under certain unusual conditions.

However, it will definitely cost more to fill your tank with 89 versus 87. :D
is there no effect on my engine if i will downgrade my octane 89 to 87 for my RAV4?
Your engine was designed to run on 87. Correct? Then I see no reason why 87 octane would have a negative effect on your engine.
thanks don.

how about if I use octane 89, is there a benefit or advantage on my rav4 engine? im just confuse with this thread.
 

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Portege_RAV4 said:
RAV4Don said:
Portege_RAV4 said:
RAV4Don said:
Portege_RAV4 said:
is octane 89 good or bad for my 2003RAV4? do i need to change to octane 87?
Going from 87 to 89 octane is not a matter of being good or bad.
Will it hurt anything? No, not at all. In most cases you and your engine will not notice any change in performance.

Will it help? No, not really except under certain unusual conditions.

However, it will definitely cost more to fill your tank with 89 versus 87. :D
is there no effect on my engine if i will downgrade my octane 89 to 87 for my RAV4?
Your engine was designed to run on 87. Correct? Then I see no reason why 87 octane would have a negative effect on your engine.
thanks don.

how about if I use octane 89, is there a benefit or advantage on my RAV4 engine? im just confuse with this thread.
You might "feel" better with the higher priced 89 octane beleiveing there is some great advantage, but there is rarely any need to run 89 octance in an engine designed for 87 octane. Run 87 octane and be happy knowing you are doing the right thing. I am not sure I can add anything further.
 
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SOME FOOD FOR THOUGHT!!

...while I understand that this topic has been "beaten to death", I wanted to add a slightly different perspective here.

While I pretty much agree with what nouse4aname has said in his post, here's a slightly different take on this. While it is generally true that 91 Octane fuel will not do much good in an engine not designed for it, there is a good possiblity that the RAV4 was designed for 87Oct AS WELL AS 91Oct .....some of the owner's manuals I've seen say "87 Octane or higher"

The reasoning behind this is, generally speaking, is that a HIGHER COMPRESSION engine needs higher octane fuel. IMO, any engine with a COMPRESSION RATIO of around 9.5:1 or above can be considered a "high compression" engine.

If I remember correctly the RAV's compression ratio is closer to 10:1, which, IMHO is pretty high!! .....so it's a distinct POSSIBILITY that although they recommend "regular" in the manual for MARKETING reasons, one could achieve slightly better performance with higher octane fuel (that is assuming the ECU has the ability change the TIMING to adapt to the higher octane fuel)

While I would like to say that the above reasoning is purely speculative, another reason for me coming to this conclusion is that I was told by a HONDA rep/engineer at the Torrance headquarters, that the Accord V6 (which incidentally also has a high compression ratio) is actually designed to achieve higher horsepower and torque numbers with 91 octane fuel, but since it's a "HONDA" and not an "ACURA", they MARKET it as needing only regular gas
 

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Victor555 & Parkwaycruiser, I believe there is some truth in what you are saying and reading. I think I need to amend my comments in posts above. While I know I am correct in my basic comments about octane and engine requirements, I found an article on this topic in a recent (June 2005) Road&Track mag that suggests there may be some benfit in newer engine management systems!

Here is the response by the R&T writer Tom Wilson to the question of using higher octane in an engine stated by the manufacturer as needing 87:

"Modern electronics is good enough that automakers are now writing engine-management software to "follow the knock sensor." That is, the ignition timing, which is already being adjusted by the engine-management computer many times per second, is largely determined from what the knock sensor is commanding. In practice this means the computer is often advancing the timing (for better power and fuel economy), while the knock sensor announces when timing is too far advanced whenever knock is detected. Then retards the timing a couple of degrees and then the process repeats. Everything else being equal, the higher the fuel octane, the more ignition timing can be run before knock occurs, and thus more power is made. Because the system is constantly at work and finely adjustable, it accounts for the various fuel blends that end up in the car's tank."

While I don't disagree with the comments by the writer above, the key point hinges on the "programming" and the capablitiies of the particular engine. From my understanding most engine programs are designed to be able to tolerate a LOWER octane of fuel than advertised in order to protect the engine from lower octane fuel usage and are not necessarily programmed able to benefit from a higher octane.

An example of this is the case of the older (pre-hemi engine) Chrysler 300C (92 octane) and the Charger R/T engines that were identical mechanically, but the R/T was 'programmed' to run on 87 octane. As I recall the HP in the 300C about 10-15 more. If one program could do it all, then there would have not been a need for a separate programming of the 300C to gain more power. BUT, the article I read about this comparision commented that folks with the R/T could get their program changed to gain the missing HP, but then 92 octane would be required. This reasoning suggests one program cannot do it all and that OEMs tailor the programs.
 
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