I agree that they recommend it for a reason. I don't necessarily agree that the reason is correct. As I understand the automotive industry, 91octane is RECOMMENDED, it's not required. They're supposed to design cars to work on the 87.

And I ran the first 10,000 last summer on 91-93. I was getting 32 mpg. I'm getting 33-35 mpg now with 87 on the highway. That's probably just from breaking the car in a little. I'm a highway cruise control driver in general.

20-40cents per gallon for 1000 gallons a year is a good savings. Now if I'm damaging the engine or turbo.. sure... a $4000 repair bill is going to suck.

 

You need a to custom tune to run 108 octane but, you'd definitely see more power because you can safely run higher boost on race fuel with out your EGTs getting to high.

 

I'm reviving this thread because I just got my A4 and was debating what fuel to run in it.

There aren't many mass market vehicles that REQUIRE premium fuel anymore. From the research I've done, RECOMMENDED octanes are a 'cheat' for manufactures. Higher compression engines can eke out a little extra horsepower with premium gas, so manufactures get to advertise their 'inflated' power numbers...but at a cost to the buyer because ultimately they will be shouldering Premium's 'premium'. Near me that amounts to $5 per fill up. Why **** $5 a tank away for a couple hp if you aren't mashing the accelerator full tilt everyday? (I never do)

There is also some debate that Premium gas typically contains more ethanol and could therefore contain less energy overall when compared against the same volume of gas with less ethanol content. Premium could actually return less MPG than Regular.

Top Tier is, as everyone probably knows, related to detergent/additives, not octane. Regardless I'll stick with TT. It usually isn't much, if any, cost difference anyway.

So for the time being, I'll be sticking with 87. I don't know if I'll miss the 5 or so peak HP as a result, but I suspect I'll be just fine.

 

your car will not knock with 87 octane fuel. most (all?) modern cars won't. that is correct. so it doesn't require high test. However, your engine will retard timing with lower octane levels. This will result in not only less horsepower and torque, but you'll also get less gas mileage. i speculate that your 02 sensors and mafs break down faster with the lower grades too, but I have no proof.

in any case, ironically, if you go with the lower octanes to save money, you will spend more in the long term. and you'll go slower. make a chart. run a full tank of 87 and plot your mpgs. then 89. then 91. then 93. run a standard route. If your experiment is somewhat scientific, I promise you'll spend less money on gas with 93 than you will with 91, and less with 91 than with 89, and so on. your car will run better with higher test too. and it will last longer.

For example, I would save about 3.50 per tank if i went with 87 instead of 93. But with 93, I can travel 31 miles farther. My car gets 21 mpg AT BEST but usually it's more like 14. So I'll go with 14 to make the point. Follow closely now: were I running 87, I would have to stop to add another 2 gallons in order to go the extra 31 miles. At $3.10 a gallon, that's $6.20. So I went from saving 3.50 at the start of the tank, to being down $2.70 only 31 miles after that tank dried up. wrap your mind around that stuff there, my friend, and you'll be in good shape.

keep in mind, with the example, my car is a little extreme, so the difference won't be as great with yours, but it's there. I've charted an A4 too. Also, as you go higher and higher in the octane levels, things get a little different. so stop at 93 or 95 for this experiment.

I dunno about the ethenal content. i hate that crap. around here, no octane level can have more 10 percent. it probably does have some effect on mpgs, but i would think it is negligible between octane levels.

 

I read an article in car and driver (or one of those magazines - I get them all) and they were testing octane vs power output. I don't remember if it also compared mpg. Anyways, they had a 2.0t from an Impreza and a supercharged six from BMW and when the car sensed the lower grade fuel the computer lowered power output dramatically for the 2.0T and little less for the super six. 2.0T was reduced 10% and the super six 5%. If our engines were limited by 10% that would be a 21hp and 26ft-lb loss. In my opinion that takes the fun out of the drive for me. I do like to mash the gas a lot though. I have been using 93 since day one and plan to for the life of the car. I only fill up about twice a month so an extra $10 a month doesn't bother me. I hear that there are quite a few people that don't use 91 or 93 so you will probably be okay if you choose not to as well.

 

In moving to the A4, I've already given up over 100 hp from my last car. Granted only 50 lb-ft torque and about 300# too.

As I look back, I recognize what type of power I really utilize, and frankly, a 100hp car would suffice.

Now I do like a bit of luxury and ergo I now have the A4. If they had offered a smaller engine (or a diesel at a fair price) I would have jumped on it. I don't know, i guess I have a true european mentality when it comes to cars: I want nice appointments and good economy.

I am open to premium gas though. If regular gives me a 10% drop in fuel economy, its a wash (mpg wise) and I'll take the premium for the extra horses (why not if they are 'free'). If the MPG drop is negligible (which I suspect it will be) then regular will remain in the tank.

A 10% impact on hp is higher than what I've generally read, but if true, I'll concede is likely noticeable. However, I think I've pressed the throttle more than half way maybe 3 times so far - no exaggeration. I'm just not a jack rabbit.

I know many are into performance and will find my mindset puzzling.

 

Using regular instead of premium gas would save me less than $100 per year, which is certainly not enough to sacrifice any performance. For those who drive far more than I do, the temptation to use regular instead of premium would be much stronger.

 

Back to the original question. So far I am not blown away by economy from the 2.0t. Seven years later, and I think my old 1.8t manual got the same mileage as my new 2.0t 8 speed. When I storm back and forth on the highway to the airport, I get 26 to 29mpg. (of course my wife did a trip this weekend, and got 31.2mpg.... She ambles). Yes I use premium gas - just always have for my euro cars.

 

You bring up a good point about the O2 sensor and MAF.

My mom has a 2007 Lexus RX350. Bought it brand new. She's been using 87octane for the last 2 years. The O2 sensor on the exhaust whatever went out last year. While it was still under warranty. Lexus replaced it, free. This year, the same sensor is dead again. It's going to be a $550-600 repair.

She's driven, maybe 30-35,000 miles in that 2 years. Certainly didn't save $600 to offset the price of the sensor.

I was putting 87octane in my Audi, have been for about a year (25,000 miles), and I stopped. I switched back to paying for Premium 91-93 octane. And I dumped in a few bottles of engine cleaner & fuel injector cleaner, etc. It's not worth the lost car time, repair costs, day off of work to go get the O2 sensor fixed, versus the $200-300 I save a year on gas.

 

your 1.8t may have gotten about the same mileage, but the power was much much less. so to get the same economy with more power is kind of a feat, ya know. And it's really what audi has been all about the last 6 or 7 years, trying to make cars go faster and burn less fuel. look at the r8. it's not just a cool looking fast car, it gets pretty damn good gas mileage for such a car. And that's why it was so dominate early on at la mans. though it wasn't necessarily the fastest car on the track, audi had to pit less than its competition, and that results in shorter laps. now the same is true of audi with the 10 cylinder TDI engines. Amazing performance and supurb fuel economy means audi continues to be the team to beat at la mans.