I'm running my '94 Q Avant with 89 Oct. here in SoCal,but the other day I filled with 91,in hope to find some improvement in gas mileage,but there is none.I don't even notice any improvement in power either,the car still a slug.I filled with 87 also in the past,seems to me the same.No change even in engine noise either,no pinging,nothing.So my question is do i make any long term harm by filling with 87?I'we noticed,that here in Ca,we get a better quality gas than elsewhere,example I shipped a Kawasaki GPz to Europe to use it there,which i used here with 91 octaine(the highest here)and in Europe I have to use 98,not eve 95 cut it,the bike was pinging like crazy.Any suggestions?

It doesn't know to advance the timing to make use of 91 octane, so'll get bad emissions (unburnt gasoline in exhaust) and no extra performance.

Its like asking five differant guys about their experience with the same call girl. Some will say it was great while others will say the recieved a burning sensation from the experience. As you stated it has been debated in length. Some like me have never experienced any short or long term adverse affects of using 87. While others have had pinging that went away at 89. Some have experienced pinging even at 89 so only run 91-93. I wish I had a better answer for you but the debate will always go on. my thoughts are, I haven't had any problems using 87 so I will continue to do so. If I had seen problems I too would have raised the rating, but not to 91-93. Which I refuse to use in anything that is not a turbo. As far as Kali goes I don't know if the emission standards there for gas has any effect on its efficientcy in a car or not. I do know that standing in front of the DMV can be hazardous to pregnant women and such because of the paint. (Per the sign) LOL but thats another OT thread. I try not to get to paranoid about gas. If I see a problen I up the octane. I also take heed to the dates on the pump inspection stickers and steer clear of mom and pop franchised stations. As underoctaning pumps has always existed, and I' sure is a lot more rampant now given the cost of oil.

I averaged about 21 mpg. My father suggested I put higher octane fuel in the car so I did (Super/Vpower 93 octane, now I get 25 avg. Thats city, and I didnt believe it the first time I checked it. But the second time it was the same. So for me it did make a difference. I have found that its best to stick with what Audi recommends because you'll end up spending more money than you save (i.e my little brake issue). Plus what do you save by using reg. $2 on a tank. I can find that in the couch.

I get 20-22 mpg combined,with or without premium gas.And I only use brand name stations(Chevron,Shell et al)

Of course with the corn in the fuel, there's no mileage improvement.

If you want to dial up your power a little, take up some of the slack in the throttle cable out at the throttle body. Not all of it, just some.

There's a "C" clip there, so just slide it up, pull the throttle cable end "out" of the throttle body bracket a couple of notches, and slide the "C" clip back in place.

Then go for a drive and see if that doesn't bring on the transmission and power a bit sooner.

Take you 20min. You have to pop that top plastic cover off the engine, and then loosen the bolts for the plastic intake plenum and move it back. You might be able to access the cable from this point if you're careful. If not, remove the intake plenum and to do that you need to CAREFULLY remove the valve cover plastic breather pipes from both sides of the plenum, and then lift the plenum up and out. Don't drop the 2 plastic locating plugs that are in the front of the plenum!

Your car is constantly taking measurements of the air/fuel ratio. Your car is designed to run optimally with 92 or higher octane. Which I believe means that the explosion that takes place in the combustion chamber runs hotter/colder with the lower octane, I dont remember which. In this case your car compensates for the disparity by adding more fuel, or using less air, or both. I dont know exactly what happens, I just know that this is what its trying to do; so that it can eliminate gas knock and try and keep the car running optimally. Guys I'm no expert but this is my knowledge as of this point. Hope this helps, if I'm wrong please let me know....

Name = (R+M)/2=RON
-------- --- ---
regular = 87 = 91
mid-grade = 89 = 93
premium = 91 = 95

The higher the engine compression ratio, the more torque produced and the more likely detonation will occur. Detonation is when the fuel-air mixture explodes all at once rather than burning evenly across the cylinder. The octane rating indicates the resistance to detonation. Pump the 12V up to 14 to 1 compression and you get lots more torque. But you might need to run 100 octane racing fuel to keep it from detonating.

12V engines have a relatively high compression ratio, around 10 to 1. For that ratio, Audi recommends 91 octane (R+M/2). A lower octane is likely to detonate at that compression. As soon as the ECM detects detonation (knock sensors), it retards the ignition so the spark occurs later in the cycle, reducing the impact on the pistons. You shouldn't hear much pinging. If you do, it's really serious and the ECM is not doing its job.

With lower than recommended octane, the engine will automatically adjust and produce less power. I suspect that the fuel mileage using lower octane will be less because you have to push the loud pedal harder to get the same acceleration and maintain the same cruise speed.

First of all, I am new to the forum. I have owned several Audi's, but my current ride is a '96 A6 Quattro.

Secondly, here is my take on this issue.

In response to Audikas post:
The oxygen or lambda sensor is used to "detect" if it is running rich ("too much fuel", will probably foul plugs, inefficient, more emissions) or lean ("not enough fuel", also inefficient, produces more heat, more emissions). ECM/PCM gets the signal and adjusts.

And on octane ratings:
The octane rating is often referred to as AKI or Anti-Knock Index. The higher the octane rating the higher the resistance to engine "knock".

When you engine "knocks" the air/fuel mixture is igniting at the wrong time, maybe cause by several things.

If you use the lower rating gasoline it does not mean your engine will start "knocking". This is because your engine is equipped with a Knock sensor. The Knock sensor basically detects the "knocking" and tells the ECM/PCM to adjust the timing to make it stop. This usually happens so fast that you don't notice.

Now the downside to using lower octane rating gasoline is that when the ECM/PCM adjusts the ignition timing you will loose power.

What it comes down to in the very end is...

It should run fine on both.

If you are going to spend the day at the track and want to get everything you can from your engine use premium.

THE END

For me there is a difference between 93 and 95 (The only fuels you get in south Africa) Even my mum who likes to give a bit of gas more than average.
She hada back operation a few years back and she now mostly drive the Audi because it is auto. We had a shortage of 95 unleaded at the time so she used 93, she moaned because she could feel the car doesn't pull enough because her back still pain alot( I know it sound funny) but the amount of G- forces created with 93 are less than with 95. As soon as the 95 came back she filled the car up with 95 and she clearly stated that she could feel the car had more g-force because her back pained less under acceleration

Now I only use 95 unleaded

They say on the gas flap 'use highest octane available' and that is what I do

I don't notice a lick of difference. I've tried several tanks of premium and the fuel mileage is identical to that of a 'regular' tank. I notice no extra power either. Only thing that seems to be different is the price to fill my car.

the biggest reason to use high octane is because of deposits which can occur while burning lower octane high octane burns hotter low octane well.. cooler.

just wanna say i have never seen a more beautifully crafted vehicle in my life. Audi sugests premium because yore engine runs optimally with that octane u can run regular but it clogs things up either use premium or octane boost. i run 103 in everything it hurts my wallet to mix fuel but i get great throttle response. the hotter the cleaner.! some engines especially small motors cant handle high octane tho but an Audi is designed for 90 grade!

Hey Mister Apprentice.....

We ran our '86 Jetta on 87 Octane. When I replaced the head gasket at....oh, 220-something thousand, the backs of the valves and intake runners looked like the day the car was built.

Octane is about ignition advance and engine compression. Build a high(er) compression engine, and you need a fuel that's harder to ignite. Otherwise you either have to dial back your ignition advance, or you get spark knock. Run a low(er) compression engine, and you can run more advance and low octane fuel.

People can run low octane in their 2.8's, but if they notice a little spark knock right as they take off, or under load, they might want to consider running 89 or 91. Those who live at altitudes will still run low octane.

C'mon man. Do your homework before you show up for class.