Running regular vs premium any real world difference ? negative impact ?

With the 1.8t i could see how you would feel the difference for sure. But with some other motors and that fact the ECU can change to meet the demands of lower or higher octane, i think its a fable.

you answered your own question

Of course it runs better on premium; that's why the manual calls for it. Yes, it retards timing if you put regular in so as to avoid engine damage due to knock.

LuckySeven said:

Am I imagining this or is there a real world difference to the average driver ? Does the computer retard the timing when using lower octane fuel or ?

Click to expand...

The computer will absolutely retard the spark and reduce boost when running low octane fuel. This will yield less power, and - in my experience - poorer mileage, though some people dispute the latter.

And with all the negative impacts your only saving like $2.50 at most which is not worth it.

I run 89 octane all the time in my '99 1.8T and I have not experienced any lack of power or significant reduction in mileage. However, I would never consider using 87 octane. VW calls for 91 octane fuel, which is not available from the vast majority of gas stations. Local Shell stations in Maryland offer premium gas for $0.25 off on Tuesdays, which is the same price as their mid-grade 89 octane, so I'll get premium whenever I have to get gas on a Tuesday. So far, I haven't noticed any difference in the way the car drives and any difference in mileage is negligible (i.e., less than 1mpg per tank). I tend to run my car until the needle starts touching the red bars on the gauge and sometimes after the dash light comes on so there's very little mixing between grades when I fill the tank.

When you look at the poorer gas mileage and the cost of premium it comes out to a wash as far as money is concerned .Use premium and enjoy the performance .

Watch the additive pack. With some brands, the higher-octane options also have more effective detergents. You may end up carbon-fouled with their lower-octane fuels.

I use 91 octane Shell in my 1.8T and 89 octane (which the gas station creates on the spot by mixing 87 and 91, since there is no underground 89 octane tank) in my 2.8 12-valve.

I wish I saw this earlier. Closed. Just read the umpteen million other threads on the topic. Since I am here....you'll probably notice the performance difference more in warm weather vs cold.