keithl

Almost all gas in a region icomes from the same distribution depot and then the only differences are any brand specific additives that are put in, that is what leads to top tier qualification. In the end all gas starts out good, but if you get it from some station that has low volume or issues with its underground tanks or water drainage. I have used Quik Trip for 10 years and never had as much as a knock, or any other issue with the fuel.

snagitseven

Why does Audi bother to recommend Top Tier Suppliers by brand name if that were true? I've been using Shell V-Power premium for years in all of my Audis, including my '01 A6 which had 100K miles and my wife's current allroad purchased in 2002, with no carbon build-up, power loss or knocking whatsoever. Other than your personal observation, I would be interested to read any specific data you can share to support your claims.

AUDIQSS

ALL modern engines, incuding Audi, use knock sensors to adjust ignition timing to stop engine knock. If the engine begins to knock, the timing will be retarded to stop the knocking. Therefore, using lower octane itself will not damage an engine. Fuel mileage and power will decrease but not necessarliy in a direct ratio to the cost of the gas. Therefore, it may be more economical to use. So if you are not racing or tracking your vehicle do as the Life cereal commercial says, "Try it, you'll like it." If not, go back to the hi-test.

I have only used mid-grade (89) in All of my Audis and had no problems with knocking or carbon and my mileage has been in line with that most others are reporting. Most of my gas has been purchased from WAWA which is normally close to the cheapest in my area. Who supplys it I have no idea.

My Audis which have been in the shop many times, but NEVER for an engine problem even remotely connected to fuel quality, include:

1998 A6 with 2.8L V6
2001 allroad with 2.7L Turbo (still in the family with well over 100,000 miles)
2002 A6 with 2.7L Turbo (also still in the family)
2004 S4 Cab with 4.2L V8
2007 A6 with 3.2L V6
2010 S5 Cab with 3.0L SC (3.0T)
2011 S5 Cab with 3.0L SC
2013 A6 with 3.0L SC

Mike_L

How do you know there was no build up or knocking? Did you pull the engine apart or log the knock retard? In this day and age of knock sensors, you will never audibly hear knock. It will pull timing way before then.

I've done several teardowns, and logged KR on tons of vehicles. Additives cause knock. The V-power additive is among the worst. Techron ain't much better. Both knock about as much as much as an off the shelf injector cleaner.

With the 3.0TFSI being so neutered in the A6, I don't see it knocking on anything. But once its tuned and allowed to make the boost it can make, then it has the potential to knock. Direct injection quenches some, I was running over 22psi on the X5M, but it can only do so much.

And for those that don't know, this is the result when a motor knocks. Absolute chaos.

snagitseven

Ok, so how do you know from looking at an engine tear down what specific brand of gas was used over the life of the car and are "several" examples enough to draw statistical validity? I've done quite a bit of searching and haven't found anything but positives about V-Power and the additives they use. Again, I'm simply looking for some hard test data to support your assertions that Shell V-Power or the other brands you mentioned are harmful to an engine.

While I don't claim to be an expert, I've always thought too low an octane is the primary cause of knocking. There are other causes but I've not seen that additives are one of them. In fact, I've read where additives can reduce knocking as this article explains.
http://www.carsdirect.com/car-repair...f-engine-knock

Mike_L

The only hard data I have is what we've seen. Whenever we get somebody complaining on the forum that their motor is knocking, or that they have no performance increase, the first question is always about which gas they're using. Almost always, the answer will be Shell. Thats caused most of the Domestic Tuners (DS, SuperChips, Hypertech) to not recommend using it. They recommend just Exxon-Mobil, BP or Sunoco. Personally, even though I have stock in XOM, I exclusively use BP in my cars.

Don't get me wrong, I don't care what you guys use. I'm just sharing data that my experience has shown. On these cars it really doesn't matter unless you're tuned.

Can VCDS log knock retard? I'm driving to Florida next week and I'm sure I won't be able to get BP in all the states going down the coast. If I can log it, I'll log the KR on all the different brands I use.

Mike_L

Too low an octane is the primary cause of knocking, or the wrong ignition timing.

Additives are definitely another big cause. Not all additives though, just cleaners. Cleaners will not burn, so they reduce the AKI. Dyno a car with just gas, and then dyno it again with a cleaner in the tank. You'll lose 3-5% of your horsepower due to a less energetic burn in the cylinders.

snagitseven

Well, all said and done, after 13 years and 300K miles of using them with no apparent ill effects and no plans to chip my engine, I think I'll stick with Shell premium and other Tier 1 brands with built-in additives until or unless I start to read testing or multiple experiences of others that shows it to be harmful.

AUDIQSS

Let me say it a different way. If you are not tuning your vehicle and/or subjecting it to extreme operating enviornments, then it doesn't really make much difference, within limits, which gas you use. Just don't try kerosene.

Tuning = Over stressing what the manufacturer built, hopefully, without breaking it.

in2dwww

I read a few years ago on a Mercedes forum about a chemical engineer who explained that while most fuel comes out of the same refinery and each brand of gasoline uses its own additives, the "cheap" gas stations often buy the fuel from the refinery that is stuck in the pipes between the refining process...

So when the refinery switches production, the pipe will still carry fuel and that's what you get from the cheap gas stations.

It's not just the additives you're paying for... it's the quality.

And octane ratings are the minimum ratings. In theory, you should be getting no less than the stated octane rating from that fuel and it would be nice to net slightly more than what you're paying for.

And then let's not even get started on the farce that is ethanol blends and winterized fuel.

This is why I have a diesel.