Gas Octane level?

[Alec07S4]

just curious with gas prices on the rise...i was contemplating filling with mid-grade gas, or lower than 93 octane which i usually use. Is there any real engine harm with using less than "super" grade gas? or is it just a marginal difference. I've heard mixed reviews amidst some search. Any advice is appreciated. I know its just pennies on the dollar but i was jsut wondering given the sharp increase in the price of gas these days...

And please... yes i know it's an S4 and i don't need the.."you shouldn't be driving an S4 if you can't buy super grade gas argument"...Thanks in advance!

[wakedude]

Just this past week I put lower grade gas in my B7 2.0T and it was the biggest mistake ever. I have it chipped with a GIAC chip and the car performed terribly all week. It was like it was rebelling against me. This morning I filled it up with premium again and now it is purring like a kitten. Don't go cheap on the gas. It is just not worth it.

[VZWalex]

Just this past week I put lower grade gas in my B7 2.0T and it was the biggest mistake ever. I have it chipped with a GIAC chip and the car performed terribly all week. It was like it was rebelling against me. This morning I filled it up with premium again and now it is purring like a kitten. Don't go cheap on the gas. It is just not worth it.

^^ what he said ... cheaper gas will cost you more in the long run .. especially if it causes major engine damage.. Will cost you less to use the right fuel

[likewater]

I wouldn't do it. Even though detonation or pinging which you may experience by using a lower grade fuel isn't really a bad thing if it happens occasionally, over an extended period of time it can do damage to your motor.

Most engines in good condition will run fine on regular grade 87-octane fuel. But engines with high compression ratios - (Audi S4 V8), or engines with turbochargers, superchargers, or with accumulated carbon deposits in the combustion chamber may require 89 or higher-octane fuel.

Anyway, I would just try to suck it up for now.

[Ill 3.0]

prob. an even worse idea as summer approaches and temps get higher. wakedude's argument doesn't really apply since that was a chipped turbo car, which was probably running software designed for 93 oct. But likewater is right, higher compression engine means you'll want to stick with the premium oct.

[b spot]

If you are stock, anything over 91 is a waste of money and will actually make you slower/less fuel effecient.

[FastB7S4]

If you are stock, anything over 91 is a waste of money and will actually make you slower/less fuel effecient.

Please explain. This is contrary to what every one else says. I would agree if the car was designed to run on 87 or even 89, but it's not. Where I live, 91 is not available, only 93 and sometimes Sunoco's Ultra 94. I'm assuming you mean running race gas or 100+ octane on a stock car is a waste.

[B6_Rakete]

I heard some guy on CNBC this morning talking about how oil prices will be at $225 a barrel by 2012.

$9/gallon premium, here we come!!!

**rethinks decision to buy an S4 instead of a Lotus Elise**

[b spot]

Please explain. This is contrary to what every one else says. I would agree if the car was designed to run on 87 or even 89, but it's not. Where I live, 91 is not available, only 93 and sometimes Sunoco's Ultra 94. I'm assuming you mean running race gas or 100+ octane on a stock car is a waste.

91 isn't available? I wish I had your problem! Finding 93 here is impossible. Actually, all we have for high octane at the pump is Mohawk/Husky 94 wich is a methanol blend (ie. it sucks).

But anyways, recommended for our cars is 91. Running on less than 91 is a bad idea for sure, but if 91 is available, it's the best choice. Higher octane gas resists combustion, and actually has less energy per volume than lower octane gas. In high compression engines with advanced timing, you need the higher octane to resist detonation. Going above the level of detonation resistance required does nothing for you though, besides filling with a liquid that overall has less energy in it.

Less energy, less performance, less fuel economy. Always go with the minimum possible.

[FastB7S4]

91 isn't available? I wish I had your problem! Finding 93 here is impossible. Actually, all we have for high octane at the pump is Mohawk/Husky 94 wich is a methanol blend (ie. it sucks).

But anyways, recommended for our cars is 91. Running on less than 91 is a bad idea for sure, but if 91 is available, it's the best choice. Higher octane gas resists combustion, and actually has less energy per volume than lower octane gas. In high compression engines with advanced timing, you need the higher octane to resist detonation. Going above the level of detonation resistance required does nothing for you though, besides filling with a liquid that overall has less energy in it.

Less energy, less performance, less fuel economy. Always go with the minimum possible.

Ok, yes. I agree with that. Run the minimum that is required of the car. I thought you were saying that running 91 is a waste and should be using 87 or 89. Believe me, if we had 91 available and was cheaper than 93; i'd be all over it.

[mus27]

So 91 is the recommended octane level in our cars? I have been putting in 93 since that's what my dealership told me.

[Speedymon]

The recommended is on the fuel door. Anything less and the ecu may pull timing if it senses detonation. B-spot is correct. Anything more than the minimum is a waste if you are not tuned for it.

[Alec07S4]

Sorry for the late reply..i really appreciate all the input guys. I probably will be sticking to 93. thanks!

[4-tified]

So 91 is the recommended octane level in our cars? I have been putting in 93 since that's what my dealership told me.

No. What is "recommended" is on the inside of the gas door, or in your manual. In certain markets, like California, they don't have above 92-93.
Thus, car makers either detune the engine or they let the ECU control anything that happens with the lower than optimal octane fuel.

So, in Canada where you can't get above 91 and the recommended fuel is 91 octane, then all is well. However, if you were to use 93 octane you may actually see a boost in performance, if you're ECU is controlling engine operation with 91 octane.

Point is, using higher octane DOES NOT give you more power. Tuning an engine to achieve higher performance may require the advantages of higher octane fuel so that it can run at that tuning level. It's NOT the fuel that creates more power, it's the tuning.

I'm in the Chicago market where we get 92-93 pretty much everywhere.
91 would work just fine too.

To the OP:
Typically gas stations have 3 octane grades; regular, mid, high.
The difference it "most" stations is about $.10 between each one.
If you were to go with regular, you save $.20 per gallon.
Your Audi takes about 16 gallons to fill up the tank.
16 X .20= $3.20
mid grade: 16 x .10= $1.60
There is your answer.
Use the recommended octane.

[mus27]

No. What is "recommended" is on the inside of the gas door, or in your manual. In certain markets, like California, they don't have above 92-93.
Thus, car makers either detune the engine or they let the ECU control anything that happens with the lower than optimal octane fuel.

So, in Canada where you can't get above 91 and the recommended fuel is 91 octane, then all is well. However, if you were to use 93 octane you may actually see a boost in performance, if you're ECU is controlling engine operation with 91 octane.

Point is, using higher octane DOES NOT give you more power. Tuning an engine to achieve higher performance may require the advantages of higher octane fuel so that it can run at that tuning level. It's NOT the fuel that creates more power, it's the tuning.

I'm in the Chicago market where we get 92-93 pretty much everywhere.
91 would work just fine too.

To the OP:
Typically gas stations have 3 octane grades; regular, mid, high.
The difference it "most" stations is about $.10 between each one.
If you were to go with regular, you save $.20 per gallon.
Your Audi takes about 16 gallons to fill up the tank.
16 X .20= $3.20
mid grade: 16 x .10= $1.60
There is your answer.
Use the recommended octane.

and that's why he has four rings