jeseds

Hey guys,
Any idea if the A4 (B9) requires premium gas or is this just recommended? Is there any harm in putting in regular gas or is it just a performance issue. Always wondered whether regular fuel is actually damaging to quattro engine. thanks!

Dibiase

The owners manual list minimum 87 octane but 91 recommend for best performance

superswiss

These engines are tuned for premium gas. It can handle 87 temporarily if you can't find premium, but it's a reactive process. The engine will knock and the ECU will retard the timing to stop the knocking. There is really no money to be saved in going 87 over 91. You'll get worse mpg and potentially more wear because of the knocking.

newmoon

The turbocharger compresses and heats up the intake air which increases the risk of detonation and knocking. That's why you should use premium gas of 91-93 octane which has more resistance to detonation.

If you use regular 87 octane and the engine starts knocking, the ECU will have to reduce boost and retard the timing to stop the knocking, but then the engine will also produce less power.

If you want to see if your engine knocks, put it manually in 3rd or 4th gear at a slow roll, or 7th gear at ~40mph and floor it, then listen for a rattling sound.

AMGE36

You can use any octane
With low octane you getting less power and better mpg.
Sample 250 max HP - with regular gas you getting about 240HP
Many drivers never going to know the difference
There is no knocks how someone is dreaming about
Be smart and practical
Read some books or publications on line how industry in usa ripping peoples off.

SYMAWD

Using a lower octane will decrease fuel economy not increase it.

It also depends on the car if a lower octane is noticeable. When my parent's had a Subaru B9 Tribeca, it would run like crap if you put regular in it.

superswiss

Just clarifying the knocking comment. There's no sensor in the car that can directly measure the octane rating of the fuel currently in the tank. The ECU can only measure octane rating indirectly by detecting early detonation aka knocking. So make no mistake, there will be knocking at times with lower octane rated fuel and the ECU will react to it by retarding the timing and decreasing boost until it stops. This may not be noticeable to the driver, but that doesn't mean it doesn't happen. The ECU will then try to advance the timing again and increase boost until it detects knocking again.

Also, as has been said, mpg will be lower. The ECU will try to compensate for the retarded timing and decreased boost by burning more fuel. So while the per gallon price of 87 is lower at the pump, depending on your driving, the increased fuel consumption may more than offset it.

Dibiase

The cost just to get premium and have the car run its best is worth the extra few dollars to me. Where I live it cost me about $8 more per tank for premium. Base on the miles I drive, it this add up to about $300 more for an entire year. Not that significant considering the overall cost of owning the car.

AMGE36

Drivetrain ? Audi Technology Portal

redherring

Whenever this question is asked on here I wonder why, if the questioner is interested in a $40-50k sports sedan, they'd want to compromise the performance capability of it for the sake of saving a few bucks. If you want to save money on gas get a Prius.