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Discussion Starter #1
I've noticed in my linear I've been pretty bad. I've been running on quarter tank like all the time, being el cheapo and putting in 87 or 89. occassionally 93 but it felt like overkill. Anyways my whole point was I put in 91 octane from sunoco and i noticed a HUGE difference in car over 89. Should I be putting in 89 or 91? How big of a difference is it?
 

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SwizzDrums said:
I've noticed in my linear I've been pretty bad. I've been running on quarter tank like all the time, being el cheapo and putting in 87 or 89. occassionally 93 but it felt like overkill. Anyways my whole point was I put in 91 octane from sunoco and i noticed a HUGE difference in car over 89. Should I be putting in 89 or 91? How big of a difference is it?
Price difference between 89 and 91/93 is about 8-9 cents x 16 galons =1.44 = does it really matter????
 

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Discussion Starter #4
I havent noticed much of a mpg change in the car. I just find it much more responsive now. Kinda no longer afraid to make closer passes on highway, feels like I got a well of reserve power that's never ending.
 

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What I was trying to say is that just use 93 or 91 that the manual specifies and it will cost you extra 2 bucks per tank.....just lay off yuppy coffee and bagles :)
 

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ricot83 said:
higher octane means more power... u guys havent noticed this yet... more power equals less mpg...
Actually, if the knock sensors are doing their job, higher octane = more ignition advance = better fuel economy (assuming the car is driven the same way).
 

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are the octane numbers in US measured in the same way as in europe? because you cant buy fuel with an octane number as low as 89 any more (probably for 20years already). our options are 91, 95 and 98. practically no-one buys the 95 anymore (only very ****ty or vintage cars), because thats the engines are optimized for higher octane fuels. most of the more modern engines are designed for 98 even. the 2.0t is 95, the 2.0T is 98 octane in europe. why would one use anything else but the fuel which is required by the engine manufacturer (and for which engine performance and fuel efficiency is optimized).
 

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bauklo said:
are the octane numbers in US measured in the same way as in europe?
No, the US uses CLC rather than RON.

CLC = ( RON + MON ) / 2

bauklo said:
because you cant buy fuel with an octane number as low as 89 any more (probably for 20years already). our options are 91, 95 and 98. practically no-one buys the 95 anymore (only very ****ty or vintage cars), because thats the engines are optimized for higher octane fuels.
Yes, in Australia 91, 95 and 98RON are the most common fuel octanes available. My wife's Honda CR-V happily runs on 91RON which is the same for most Australian cars.

bauklo said:
most of the more modern engines are designed for 98 even. the 2.0t is 95, the 2.0T is 98 octane in europe.
Hmm, this is different to Australia. The manual for my car says the engine is optomised for 95RON fuel.
 

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I started a thread on this a few weeks ago.

Here in the uk we have 95 Ron (standard unleaded) then super unleaded that is 97 RON for BP and Esso (exon) garages.. and 98 RON for shell super unleaded (optimax fuel)

I was just running standard unleaded at first.. but now i've changed to super.. preferably Shell 98RON

There is for me anyway a definate performance boost using 98 RON fuel. going back to 95 feels like sapping the engine of power now. And I've also found and test fuel consumption. I get better mpg by as much as 1.5 -2 mpg on average with super. Ofset that against the cost and to be honest, I ended up spending a few pounds more a week when going back to regular.. so its better for the engine, better mpg, better performance and when measured against the improved mpg i get.. actually cheaper even though at the pumps its around 5p a litre more

Shell optimax is the fuel i try and use the most but i'll happily use Esso super as well. this is 97 RON and does feel a little down on power (no i'm not imagining it! :p) but esso is selling their super (at my local stops) a good bit cheaper too.
 

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Discussion Starter #11
Well after my extensive research * filling up on completely/near empty tanks with a total grade* There is a difference btween 89 and 91 octane. I think 93 is overkill in car system, doesnt seem to process it well. This statement applies to 175 2.0t engine system. Manual recommends 90, I have never found 90 in nyc/ct area but 91 seems a hell of a lot closer than 89 based on how responsive acceleration has become. The car is constantly Hitting 1st orange bar on boost. In 87 the car is real sluggish. In 89 only a slight improvement but in 91 it is really dramatic. I dont notice a difference after that btwn 91 and 93.
 

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In Sweden, we can choose between three unleaded varieties;
95, 96 and 98. I go for the 95, because that´s what it says under my lid :roll:
You telling me I can get better effect from using 98?
 

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Deli-Llama said:
Actually, if the knock sensors are doing their job, higher octane = more ignition advance = better fuel economy (assuming the car is driven the same way).
But higher octane gas takes longer to burn, so if the octane is too high there will be some unburned gas that simply gets burned in the cat converter instead of in the cylinders.

And with more engine power because of advanced timing with the higher octane gas, most people will use it to accelerate faster rather than hold back on the throttle.

So generally higher octane gas will give poorer mpg, but better performance.
 

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hnnng, cant resist it..:

what i (hopefully correctly) remember from studying is:
high octane fuel doesnt take longer to burn, it delays ignition.
modern engines, especially turbocharged ones, have high compression ratio, high mean pressures and also high maximum pressures. this is why fuel has to be used which has a higher ignition delay.
if the fuel were to ignite easily, you would have to delay the injection a lot in order to limit max pressure to allowable limits.
if this does not happen, knocking occurs, because the fuel ignites to early and ignition pressure rises very steeply whichresults in very high pressures.
because of this, the injection must be delayed when a lower octane fuel is used, which in turn results in a pressure curve which is more flat.
in general: early injection=high pressures, good fuel economy, late injection=low pressure, less fuel economy.
so if you use fuels which the engine is not designed for, the knocking sensor will delay injection which will result in less fuel economy. with the proper fuel, this does not happen, so not only do you get better fuel efficiency, but also more power (area under pressure curve greater(generally speaking)).

uhm, end of lesson;oops:

basically i just wanted to contribute that it really doesnt make sense to use any other fuel than the one that is recommended, but things got out of had while writing:cheesy:
 

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Engine management systems deal with different fuel grades by retarding or advancing the spark timing. You can run more advance with higher octane.
http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html

If you want 90 octane, just do a 50/50 mix of the 89 and 91. That's all the pump does. The tanks in the ground only contain the lowest and highest grades. Any mid-grades are mixed by the pump.
 

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wrp said:
And with more engine power because of advanced timing with the higher octane gas, most people will use it to accelerate faster rather than hold back on the throttle.

So generally higher octane gas will give poorer mpg, but better performance.
ok ... just bad logic here ... you are saying that because higher octane gas gives the car more performance, people will drive the car harder & get less mpg, and that means higher octane gives poorer mpg. Well ... driving the car harder will give poorer mpg ... not the fault of the fuel.

What you are saying is like saying "People will eat more chocolate chip cookies than ginger snaps, and that means chocolate chip cookies make you fatter than ginger snaps!" When it is the eating more of any kind that makes you fatter ... not the type of cookie.
 

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So while we are on the whole fuel thing, what is the story with fuel additives? I used to drive a Nissan Maxima and every 5,000 miles or so I would add ChevronPRO-GARD® Fuel Injector PLUS Intake Valve Cleaner. This always made the engine seem more powerful and the car run great. Is this stuff advised for the Saab? Can this stuff hurt the car? What does Saab recommend?


 

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quick question. the label in my arc says AON, so what does the "A" stand for? it says AON 90, and like i know what RON and MON are, but not AON. i just use 91 since it's either that or 89, and i'm too lazy to mix 89 and 91:cheesy: i filled my car up for the first time yesterday (it's only a week old) was suprised at the 90 grade recommendation, as we don't have that!
 

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gambit526 said:
Can this stuff hurt the car?
this question has the potential to spark a near religious dicussion between additional additives believers and non believers...

oh, and i'm a non-believer of course:D
 

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Discussion Starter #20
gambit526 said:
So while we are on the whole fuel thing, what is the story with fuel additives? I used to drive a Nissan Maxima and every 5,000 miles or so I would add ChevronPRO-GARD® Fuel Injector PLUS Intake Valve Cleaner. This always made the engine seem more powerful and the car run great. Is this stuff advised for the Saab? Can this stuff hurt the car? What does Saab recommend?


I've been told NOT to put any additives in car by various dealers i've taken car to shop to be worked on and even local pepboys/autozone guys. The car is self-sufficient when it comes to stuff like that such as the oil and gas etc. The only thing u would ever have to add something to is the windshield wiper if u had an 03 launch car. They would freeze in cold conditions so they added some lotion thing to the solution and fixed the problem.
 
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