[proceded1]

I have two gas options near my new house - one is 93 with 10% ethanol and the other is 91 without ethanol. Which would be the better option for a proceeded 335?

[Ilma]

The ethanol additive makes gas a little less powerful, but increases its resitsance to detonation, which is probably more important of the two when running the higher boost pressures associated with a tune.

The thng to be weary of is whether your local station is actually using just 10% ethanol.

Some people have reported samples taken by the dealer which read as high as 20% ethanol and that is definitely beyond BMW's own guidelines and might cause driveability/fuel system issues.

I have been running 94% octane with 10% ethanol for 8,000 miles and not experienced any driveability issues at all.

[dkvby]

higher octane better for the engine/performance/procede, but the ethanol just bad for the fuel pump?

[MaxL]

Originally Posted by dkvby

higher octane better for the engine/performance/procede, but the ethanol just bad for the fuel pump?

+1

But in addition to that ethanol gives you less power (lower energy content in fuel) but in theory higher octane gives you more power - I wonder which effect is stronger. I'd probably use non-ethanol fuel in this case.

[Ilma]

Originally Posted by MaxL

+1

But in addition to that ethanol gives you less power (lower energy content in fuel) but in theory higher octane gives you more power - I wonder which effect is stronger. I'd probably use non-ethanol fuel in this case.

Hmmmm....lets think about this.

Higher octane does not give you more power. It gives you greater resistance to detonation which means you can run higher timing advance, and that is what gives you the additional power - since ignition can now occur under more compression.

Boost and timing are what give you the power......higher octane fuel just allows for higher heat levels that come along with power.

So running a tune = more boost = more power = more heat = more chance of detonation.

Ethanol = less energy content, but higher octane.

Higher octane = more resistance to detonation.

If 93 octane can be sourced without ethanol, I would choose it. But in this case, the OP's only choice without ethanol is 91.

You will make more power and have less knock on the higher octane.

[marty_mcfly]

91 without ethanol

[newbieman78]

http://www.cybergifs.com/faces/Jump2.gif