idl

Well I certainly wouldn't want to sacrifice performance. What I really want to know is if there are any performance/efficiency differences between 91 and 94.

Sounds like some people get better mileage with 94, is there an actual scientific explaination supporting that? Why wouldn't Audi recommend 94 then if the engine runs better with it?

idl

Another factor in regards to range is if the car is Quatro or not.
reading my manual the other night (assuming I read it right) I noticed that the Quatro has a 63L gas tank and the non-quatro has a 70L

1move

iTrader: (1)

YUP, that is true!

rusty_67

iTrader: (1)

Basically the higher the octane the higher the combustion temperature. Now since higher pressure equals higher temperature, the octane you need is based on your compression ratio (volume at bdc : volume at tdc) and the amount of boost you are adding. I have a NA 3.0 V6, and I believe the compression ratio is 10.5:1 or something. My car runs great on 91 octane, no point in using 94 except for the fact that some companies add extra additives to their 94 that will help clean your engine and in turn may improve your mileage performance over time (not very much).

Now when running the 1.8T your compression ratio is either 9.3:1 or 9.5:1 depending on the year, however, you have to take into account that the air you air putting into the engine is not at atmospheric pressure (the turbo compresses the air). This is why your octane must change if you chip. Typically when you chip your car it will add boost pressure which ups you combustion pressure, and in order to avoid detonation (combustion before the piston has reached tdc) you need a fuel that will hold out under the higher pressure.

So, scientifically speaking, a higher octane fuel like 94, will help your performance if you are running enough boost. As far as adding performance at your static CR, no.

If you aren't chipped for 94, I would suggest running 91 and if you want to keep things clean and efficient, buy a case of fuel injector cleaner and add it when you fill up.

idl

Thanks rusty, i'm leaning towards using 91

I have a 1.8T stock. So when I put 94 in, the computer will adjust the timing accordingly is that right?
But the performance wouldn't change?

wanthema

this isn't true UNLESS u either remap the fuel line (chipping it or flashing the ecu to make the car perform better).

higher the octane, the better the stroke of combustion will be for the spark plug to ignite. You make it sound like the higher the octane, the worse it is for the car rusty. Better fuel = better performance, why else would u not put 87 than 91? like u said, higher octane = higher temp.. so lower ur oct = much higher temp = weaker performance. think, the shittier fuel you put into your engine, the shittier the combustion output it'll give u because it'll ignite before it even reaches the spark plug which ****s ur engine up real bad. This is a GERMAN car bud, not a freaken honda civic where u can put even water and it'll still run.

higher pressure is when u chip it, or really aggressively step on the pedal (and this u do NOT want to do if u fill 87-89 octane), yes the timing will change, but if u keep it pretty low, your engine will eventually give u more downtime later on down the road.

yes your car runs great on 91 because it requires you to put it. Point is do u want to keep your car for a long time or are you a dumb enough to disagree with that?

difference between 91 and 94 isnt a big difference ill admit to that, but its cleaner none the less and gives the engine a better fuel to run with. if you dont clean your fuel injectors at all, putting 94 oct will help u reduce clogging and better emissions.. studies even show that.. dont tell me your smarter than those who invested billions of dollars to prove that this is a factual result.


idl: back to your question about why dont audi recommend you 94 octane is because not all areas provide 94 octane.. at best they only provide 91, 93, and 94 in rare locations.. thats why they made it standard at 91.

wanthema

performance would change slightly and better mileage. zzz

projects

94 octane won't be cleaner than 91 or 87. The number is just nothing about clean. It's just about detonation resistant. you may say it'll burn higher temp to make combuster chamber cleaner than low number, but it's not really can be tell, since the burning temp just very small diff which won't burn more carbon to ash. Higher number is more able to resist detonation which is needed for high compression engine. The engine control system use knock sensor to detect detonation to advance the ignition timing as much as possible which will general more power in same volume gas. So chip or not, engine will try it self to not to make detonation to make the max performance. It's just kind of balance between several things. You think it'll get better gas/km, but you paid more on gas, so you don't save any. But for better life of your car go for factory rec, higher won't help, lower still can run, just not that much power.

wanthema

like i said before, my car hasn't cost me anything yet in terms of parts like replacement. been running 94 everytime.

if u love your car u give it the best, if you dont ull give it less. gas difference compared from cheap gas to good gas is 5 bucks difference, so u save 5 bucks... on a tank.. want a high five?

w/e, its your car.. your problem.

Espritman99

I am with projects. The number means nothing about how filtered or clean the fuel is. The octane number comes from how much iso-octane and heptane mixture they have blended with the fuel.

Also your comment about higher octane = higher temp and then you go on to say that a lower octane makes for way higher temps. Lower octane should make for lower temps then. Octane just has to do with the resistance to explode. So 87 octane will ignite a little sooner than 91 and if you have an extremely high compression, high revving engine this could lead to pinging and pre-detonation. However, the ecu notices any of these things much quicker than a person would and corrects accordingly. Once it has done this the car should perform as normal with miniscule fuel consumption and power differences.