I've been running Sunoco's 94 octane ethanol blend all summer and with the coming colder temperatures, have been thinking of going down a few levels, 91 or 89 octane - low enough to not experience pre-ignition (knock/pinging).

What are your opinions on this strategy? The idea is to achieve more complete combustion in colder operating temperatures. Benefits would be reduction in unburnt fuel, less fuel in oil contamination, fuel economy = money in the bank.

PS - the lower the octane, the less pressure/heat required for ignition. And I'm unchipped.

Since you said you are unchipped, I'm assuming you have a turbo motor. From your sig, it looks like you have a B6 body so I guess you have a 1.8T?

Under this assumption, I doubt you will see any real gain in fuel economy going to a lower octane fuel. In general, your fuel economy will be worse in the winter given the increased time it takes for you engine to get up to operating temperature. For example, cold engine oil is more viscous and will increase frictional losses. Beyond this, our cars are designed to reduce timing when it gets really cold to compensate for the denser air charge. By using lower than recommended octane gas (I think 91 is the minimum), you will be forcing the ecu to reduce timing even more. This will further reduce available power for little to no benefit. As long as there is enough oxygen in the cylinder, combustion of 94 octane fuel will be as complete as combustion of 91 octane fuel. The only difference is how much activation energy is required. This also means there will be no difference in fuel in oil contamination.

Even if you don't believe me up to this point, consider the $0.02 cost difference between a litre of 91 & 94 at Sunoco. Assuming you have a 60 litre tank, that's a $1.20 savings per tank for lower octane gas. It just doesn't seem worth it to me since there are no other obvious advantages to using 91 compared with 94.

--RGL

the fact that in winter you can get away with running low octane fuel. its the same when you live close to the sea level (you dont' need high octane fuel).

so going with a lower octane will help the engine warm up faster; as well as maintaining that optimal temperature when its -20C versus 20C. The added effect is less engine wear given that the engine will warm up faster.

I posed this question because my previous car used regular 87 octane. So this is a pointless strategy. Seeing if Audi owners in Canada have tried switching gas during the winter.<ul><li><a href="http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html">Gasoline FAQ section 7.10 What is the effect of air temperature?</a></li></ul>

ECU swap requires dealer participation.

and i was putting 200km/day on my car.. (i was working quite far).. so i did a research and thats what i found (abour running lower octane in cold climate)... u can safely go down to 89 or even 87 if you want.. really.. may be you can look up in the archieves of AW... but again like Ryan in TO said, savings aren't gonna be that significant, unless if you were putting 200km/day like i was last year... of course i only did that for really really cold winter months. I run 91 or 94 right now. mine is 2.8 btw... but i think u should be better off with running premium gas and dont' get those bad carbon deposits!!

Colder air temp can reduce knock, but I wouldn't go below the recommended 91. 94 is probably overkill if you're not chipped with 93/94 octane program anyways, unless you track you car on a hot summer day.

Sulphur!!! Sulphur creates pollution both directly in the form of emissions and indirectly by slowly redering your catalytic converter useless. Put enough sulphur in your cat and even non-sulphuric pollution rises.

The Suncor refinery in Ontario produces fuel with a comparatively low 200ppm of sulphur. The 94 octane is further refined to 50ppm. The only other thing in this range is produced by Irving Oil in the maritimes and isn't available around here.

Sulphur reduction alone is worth at least a $1.20 a tank.

Too bad the best we Calgarians get is 91 craptane :-(

When it comes down to AoA versus little me, EPROM changes are easy to detect.

Yes, cleaner gas is the #1 reason I fill up at Sunoco and avoid Esso.

Will have to stage some real world tests with 94 versus 91, versus 89 octane to see how the engine performs in sub temperatures.

maybe I'm wrong but I thought I read in the 97 manual

but if it a blend of gasoline and menthanol
87 or higher is ok and no more than 3%

the minuim is 87 AKI or 91 RON

but better safe the sorry

Initially the Auto Makers' Choice^TM gasolines will be sold at three Ottawa-area MacEwen stations and will be monitored for consumer demand. The three MacEwen stations that now offer Auto makers' Choice gasolines include Bank and Catherine in Ottawa, 1741 Cyrville Road in Gloucester, and 3420 Carling Avenue in Nepean. The Canadian Vehicle Manufacturers' Association's "happy pump and happy car" logo will be prominently displayed at these three stations to let the customers know it is available there.

Wow!

Please let me know all of the specifications of your rims &amp; tires and brakes including where you got them from.

TIA