mbuskuhl

True or not true, can it be done? I've read that it may be possible to use Star and change the octane setting to 93 and improve performance? I use 93 octane right now anyways, it's readily available where I live.

This is not a "is regular gas okay to use in the W211 debate" thread but rather can performance gains be realized with 93 octane and a little coding?

Other reading material: https://mbworld.org/forums/w211-amg/161184-how-do-you-change-93-octane-setting.html

https://mbworld.org/forums/showpost....37&postcount=7

lkchris

Your car is designed for high octane, i.e. premium fuel.

It has a knock sensor that will retard timing when it encounters pinging caused by use of lower octane fuel.

You seem to think this system computer has a built-in maximum ignition advance that can be overcome by manual programming and that the difference between 91 and 93 will be noticeable should more advance be applied.

Octane by itself makes no difference as to how much power your engine develops. It only allows performance enhancements to be feasible by preventing knocking. The only change that can be made electronically is ignition advance, and you seem to think more is possible and that the advance provided for 91 octane is not the maximum feasible.

Interesting.

mbuskuhl

I'm just trying to verify what I read elsewhere. I have no idea if this is true, can be done or even makes any difference on performance.

Is something that can be done on the E55 or are people just misinformed including the quote from Kleemann?https://mbworld.org/forums/showpost....37&postcount=7

sgaar

Strictly speaking that is not entirely true. The higher octane gas the more additives and less gas per volume. Gas burns better than additives, so on a theoretical level you should get more bang with lover octane gas.

With that said the reason for engines needing higher octane is that they have a higher compression ratio. If you run low octane gas in a high compression engine you run the risk of the gas/air mix ignites before the piston reaches the top thus demising the output and ruining the internal components most noticeably the piston. In modern engines you have a sensor that detects if the mixture ignites before reaching the top and it will make the computer change the ignition cycle to try to compensate. The problem is that even with knock sensors the problem will not completely go away and it gets even worse when the engine gets warm. With a warm engine the gas/air mixture ignites even easier.

So the only way you can get the engine reliably to run on lower octane is to lower the compression ratio. This is not something I would recommend that you do for obvious reasons.

mbuskuhl

Any experience? Performance improvement? I found these screenshots which appear it can be done.

http://www.infopages.net/renntech/fu...ings/index.htm

MB-BOB

As mbuskuhl points out, premium in the Dallas area is 93 octane at virtually all stations. Can't remember seeing 91 octane anywhere in this part of the country.

The owner's manual says to use 91 octane for best performance, so I suppose it's logical to wonder if 91 is recommended, can 93 be better if the car is tuned to use it. But, other threads on this topic concerning people using 100 octane show no change, other than a faster and deeper drain from the wallet.

At times, I have added 1/2 tank of midgrade (89 octane here) to an existing 1/2 tank of 93 octane, thinking the mix will yield something in the middle (closer to the recommended 91 octane). I see no less performance than a full tank of 93.