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Discussion Starter #1
yesterday i put a bottle of gum-out fuel injector cleaner in the tank before filling up with super, ( i always use super ) and topped off the oil with a quart of 20/50 weight oil. is it my imagination or did i immediately notice a big difference ?? i noticed something right away, but i'm not sure if the gum-out could have even made a difference after 20-30 miles. also, about 2 months ago i did a major tune and maintenance on the car and just now it seems like everything is seated and running smoother than right after i did the major tune + maintenance is that possible ?? thanks for the feed-back. :confused:
 

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Well, your car might be faster after you filled it up with 'super'. That would be because your wallet is so much lighter now the car has less weight to drag around!

Using higher octane than the engine is designed for is, at best, a waste of money. You will not get more horsepower that way. In fact, higher octane fuel is so rated because of a resistance to knocking. That resistance comes about due to the higher octane fuel's slower burn rate.

The S4 Spiders do require high octane fuel. They have higher compression pistons - the engine is designed to take advantage of high octane fuel. The little picture next to your username looks like an S3 Spider. Unless it has been modified with high compression pistons, you needn't waste your money on high octane fuel.
 

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Discussion Starter #3
i dunno, i always use super...... what is it, an extra $1 or $2 per tank ?? ..... it isn't a significant amount of money. all my cars use super.... volkswagens, bmw's etc. i thought i even read in the owners manual that my 88 spider should have 93 octane.... the highest i can get here at the pump is 91.
 

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higher octane, unless you have high compression ratio pistons or a HIGHLY modified engine, is a waste of money... do you always use 20/50 oil??? i have a beat around mazda truck with a lot of ring where and i notice a change when i use the thicker 20/50 as opposed to say 10or 5/30.
 

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Discussion Starter #6
do you always use 20/50 oil???

when the oil ws last changed it was 10/50 , but i couldn't find it always, so i put a quart of 10/40 in it last time...... this time i found 20/50 and it seems to run better.
 

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Mine runs fine on 87 or 89, and is noticably harder to start and keep a cold idle going til it warms up using on the 91-93 grades. (harder to ignite as Eric describes)

As long as it's not knocking or pinging, there's no need to go to the high dollar end of the scale for fuel. (and even then I'd question the ingition timing first, unless there's been a significant boost in compression somewhere along the line)

But if you feel compelled, I'm sure the local FastTrack or simular will sell you 104 octane for around 6-8$ a gallon since you don't mind the 'extra couple bucks per tank'. :D (oh c'mon now, it's the same thing: a couple dollars a tank now over X years still adds up to a crapload of more or less wasted money ;) )

Query: did this supposed increase in performance happen to occur at a slightly cooler ambient temperature than what you normally drive in? (no, 20-30 miles isn't enough for the injector cleaner to do it's job)

If so, that would explain it right off as more power is produced at colder temperatures, and it becomes especially noticable if you're talking around 20-30 degrees cooler than what you normally drive in. (drive somewhere during 80 degree heat in the day, then come back by the same route at night when it's 50-60 degrees and you will notice the power difference on the return trip)
 

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Discussion Starter #8
do you get higher mileage using 91 octane ?? the increase in perceived performance was probably the added thick oil. what do y'all think about the idea of a break-in period after a major-major tune ??
 

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Really shouldn't be a break in persay after a major tune-up. Everyhting is settled in within a few hundered miles after a rebuild, and all the tune-up does is get things into proper adjustment/spec.

For myself, I get a couple more mpg with the lower octane stuff. (literally only 1-2mpg tops, if that much, if I'm not wailing on it constantly, but it gets at least 2-3 good blow-outs every tankfull)
 

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Mileage has to do with the calorific value of the gasoline, not Octane #.

Gasoline is not a static formula, it is a blend of several hydrocarbons that are available to blend for gasoline at the refinery. Even with the same brand, it will vary depending on what the refinery has more or less of an/or if one of the refining units are out of service. Also the "branded" gasoline you normally buy regularly could very well have been supplied by another companies refinery altogether to save on shipping/trucking costs or as a "loan" between companies. I'll lend you X million gallons of regular while you fix your hydrocraker, and you pay me back when I do maintenance on my Platformer next Fall... (a little syplified to make the point).

Also any gasoline that contains alcohol blended into it will yield less MPG!!

Who says? I say, as an engineer that worked for one of THE major refiners in the US (21 years). Also note in the Wall Street Journal that Gasoline is a COMODITY and bought and sold as such and can and does come from all over the world. Just like wheat and pork bellies.

BTW it takes more energy to produce higher octane gasoline, so you are not just lightening your wallet, but also you are contributing to energy waste and of course global warming.

TTFN Elio
 

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Discussion Starter #11
well, isn't there any benefit at all to using super ?? what about when the mfg specifies it ? i am buying a 2007 bmw 335i and i wouldn't think of using anything other than 'super' in it.
 

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Yes you use the gasoline the manufacturer specifies with respect to octane #.

We are discussing here your S3 Spider I thought. It runs happily on Regular gas.

Your 2007Bmer 335i is designed to require higher octane. If you don't satisfy an engine's octane requirement it will not give you design performance.

Most current hi performance modern cars have a "knock sensor", should the octane requirement not be met, the ECU adjusts the spark timing (advance) to stop the knocking. This usually means a small reduction in performance. No one is suggesting that you should put lower octane into an engine than the manufacturer recommends. But Tifosi, rightfully said that if you put Hi Test in a car that will run happily on Regular, all you accomplish is a lightening of your wallet and energy waste as I pointed out.

Best regards, Elio
 

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back to the start.." gum-out fuel injector cleaner"..." is it my imagination or did i immediately notice a big difference ??"

it is not uncommon for the injector cleaner to bring back life to a old/slow O²
and if your O² was not working or slow that can affect performance.
or the feel..
 

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Bah, all my O2 sensor does, slow reading or otherwise, is run an A/F gauge. (oh, wait, aftermarket EFI..... :D )

But yes, in the L-jet, it can certainly make a difference in how it goes about things.
 

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Discussion Starter #15
okay, so my 1988 doesn't need 91 octane, then should I buy the lowest or medium octane.... i think most gas stations offer 3 types.
 

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In the USA you should use 'regular' in your S3 Spider. In most markets that'll be labeled 87 octane (R+M/2). It'd be the cheaper price. Except that I've seen Sunoco pumps that have an extra low octane fuel available (85 IIRC). I assume that's so they can post a huge sign near the road with a cheap price (and the low octane number in small letters).
 

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You have more than enough octane for your 1988 Spider (if unmolested) with the Lowest Octane grade, Regular.

Proof of the pudding: Fill up with REGULAR and run your car agressively, under load, if it does not ping/rattle on acceleration your octane requirement is satisfied...nuff said?

AS for your other cars, follow the MFR's recommendation..

Bottom line buying more octane than your engine requires, wastes money and refining energy, period!

Elio
 

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Discussion Starter #18
okay i put in a tank of medium grade 89 octane.... i don't know if i can bring myself to use the 87. shoud it run better on on 89 or 87 than on 91 ???
 

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It shouldn't run better/worse on 87 than 91, it'll just run cheaper. As stated, as long as you haven't advanced the timing and it's not pinging on 87 you should be fine.

Now, back when I worked for Amoco I used to run Amoco Ultimate 93 in my car even though I didn't need it. Reasons were threefold:

1) Gas was cheap at the time (this was late '90s when oil was under $20 a barrel versus $70 now) so the cost difference was minimal
2) Amoco Ultimate was the only gas you could buy in Chicago at that time that didn't have 10% ethanol, so it had higher energy content (better for mileage)
3) I knew the actual process units that the fuel came from at the refinery outside of Chicago, and specifically that it was a cleaner and lower-sulfur fuel

1 & 2 are no longer true, however, so I wouldn't do it now.
 
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