I have a few of these too 
100 octane fuel question
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Joined: Aug 2004
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From: NJ
2005 E55
I have used 100 octane from time to time at the track because I needed gas, not because I ever thought it would increase performance. The only way that I could see it being beneficial on a stock tune is if you are running on a hot and humid day. But that begs the question - why go to the track in the first place?
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211-55
No difference for me, but my only gauge is my 50-70mph stopwatch tests I do every other morning - same place, same time, and almost same temps. I filled up half tank 100 octane along with 1 gallon of 91 octane and even let the ecu adapt for over a hundred miles of driving. Best time with 91 octane: 1.49, best time with VP race gas: 1.76 
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Joined: Jan 2005
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From: Bay Area
2015 E63S, 2018 E63S
No difference for me, but my only gauge is my 50-70mph stopwatch tests I do every other morning - same place, same time, and almost same temps. I filled up half tank 100 octane along with 1 gallon of 91 octane and even let the ecu adapt for over a hundred miles of driving. Best time with 91 octane: 1.49, best time with VP race gas: 1.76 .
.Last edited by Hammer Down; Oct 9, 2009 at 11:49 PM.
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211-55
That makes sense. Another time I dyno'd with near 100 octane fuell and the tech said I was running too rich up top. I'll try using less race fuel next time I'm hitting the dragstrip or dyno.
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Joined: Apr 2009
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From: Tacoma WA
Bicycle
Running rich has nothing to do with octane of fuel, Being "rich" means the ratio of air to fuel is not correct.
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Joined: Apr 2009
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From: Tacoma WA
Bicycle
Race fuel or higher octane will only show an improvement if the engine can use that level of octane, this is going to be subjective because the 55 computer is an adaptive and it seems to be kinda slow on the adaptation? throw in 100 oct fuel without resetting the computer and you’re not going to see any change, reset the computer and make several hard pulls and that when you should see a difference. It’s been my experience that a rest of the ECU is not the most aggressive tune the ecu can produce, If I reset the ecu at the track the car will go faster and faster every pass. My fastest times have always been my last few. That’s been my experience anyways.
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Joined: Jun 2004
Posts: 1,880
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From: Seattle
05 E55
Race fuel or higher octane will only show an improvement if the engine can use that level of octane, this is going to be subjective because the 55 computer is an adaptive and it seems to be kinda slow on the adaptation? throw in 100 oct fuel without resetting the computer and you’re not going to see any change, reset the computer and make several hard pulls and that when you should see a difference. It’s been my experience that a rest of the ECU is not the most aggressive tune the ecu can produce, If I reset the ecu at the track the car will go faster and faster every pass. My fastest times have always been my last few. That’s been my experience anyways.
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MBWorld Fanatic!
Joined: May 2009
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211-55
MBWorld Fanatic!
Joined: May 2009
Posts: 1,044
Likes: 2
211-55
Race fuel or higher octane will only show an improvement if the engine can use that level of octane, this is going to be subjective because the 55 computer is an adaptive and it seems to be kinda slow on the adaptation? throw in 100 oct fuel without resetting the computer and you’re not going to see any change, reset the computer and make several hard pulls and that when you should see a difference. It’s been my experience that a rest of the ECU is not the most aggressive tune the ecu can produce, If I reset the ecu at the track the car will go faster and faster every pass. My fastest times have always been my last few. That’s been my experience anyways.
MBWorld Fanatic!
Joined: Jun 2004
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From: Seattle
05 E55
I found a Shell station this weekend and filled up 1/2 of 100 and 1/2 of 92. I don't know, but immediatly after I left the station, the car felt sluggish....like I had four passengers in it. So I drove it about 50 or so expensive miles 
and the car seemed to feel a little bit better. But the weather was in the 30's, so I'm not sure if that had something to do with it. But it just wasn't itself.
Anyway, it scared me enough to not consider doing that again. I found this thread where Marcus Frost actually dynoed his car with different octanes..
https://mbworld.org/forums/w211-amg/...ctane-gas.html
Anyway, I'm with the school of thought that if you car is not tuned for it, anything over 93-94 is a waste of money.....and possibly power. I filled back up with 92 this morning and the car feels right as rain.
And with saving $7.50/gallon of 100 octane, I feel right as rain as well.
and the car seemed to feel a little bit better. But the weather was in the 30's, so I'm not sure if that had something to do with it. But it just wasn't itself.Anyway, it scared me enough to not consider doing that again. I found this thread where Marcus Frost actually dynoed his car with different octanes..
I've tried this with my E55 and documented it - ZERO HP gain, and the car actually runs worse on anything above ~93ish octane. The ECU mapping just does not give headroom for extra timing or anything above that octane, so it is a total waste.
Remember - the rule of thumb on octane is you want to use the LEAST amount of octane before the car detonates/preignites/etc - higher octane is harder to burn (ie, requires more ENERGY) and unless you can actually take advantage of it, will net LESS HP all factors BEING EQUAL.
Good luck,
-m
Remember - the rule of thumb on octane is you want to use the LEAST amount of octane before the car detonates/preignites/etc - higher octane is harder to burn (ie, requires more ENERGY) and unless you can actually take advantage of it, will net LESS HP all factors BEING EQUAL.
Good luck,
-m
Anyway, I'm with the school of thought that if you car is not tuned for it, anything over 93-94 is a waste of money.....and possibly power. I filled back up with 92 this morning and the car feels right as rain.
And with saving $7.50/gallon of 100 octane, I feel right as rain as well.
MBWorld Fanatic!
Joined: Jan 2005
Posts: 4,276
Likes: 28
From: Bay Area
2015 E63S, 2018 E63S
I found a Shell station this weekend and filled up 1/2 of 100 and 1/2 of 92. I don't know, but immediatly after I left the station, the car felt sluggish....like I had four passengers in it. So I drove it about 50 or so expensive miles and the car seemed to feel a little bit better. But the weather was in the 30's, so I'm not sure if that had something to do with it. But it just wasn't itself.
Anyway, it scared me enough to not consider doing that again. I found this thread where Marcus Frost actually dynoed his car with different octanes..
https://mbworld.org/forums/w211-amg/...ctane-gas.html
Anyway, I'm with the school of thought that if you car is not tuned for it, anything over 93-94 is a waste of money.....and possibly power. I filled back up with 92 this morning and the car feels right as rain. And with saving $7.50/gallon of 100 octane, I feel right as rain as well.
and the car seemed to feel a little bit better. But the weather was in the 30's, so I'm not sure if that had something to do with it. But it just wasn't itself.Anyway, it scared me enough to not consider doing that again. I found this thread where Marcus Frost actually dynoed his car with different octanes..
https://mbworld.org/forums/w211-amg/...ctane-gas.html
Anyway, I'm with the school of thought that if you car is not tuned for it, anything over 93-94 is a waste of money.....and possibly power. I filled back up with 92 this morning and the car feels right as rain.
And with saving $7.50/gallon of 100 octane, I feel right as rain as well.
MBWorld Fanatic!
Joined: Jun 2004
Posts: 1,880
Likes: 9
From: Seattle
05 E55
MBWorld Fanatic!
Joined: Jan 2005
Posts: 4,276
Likes: 28
From: Bay Area
2015 E63S, 2018 E63S
MBWorld Fanatic!
Joined: Jun 2004
Posts: 1,880
Likes: 9
From: Seattle
05 E55
Well I do know that my first two times to the track I used 95 and my best trap was 117.7 and my third time at the track I tracked 118.6 and you know the story with the last vist 118.2-119.2 the 3rd & 4th visits to the track were on 101/91 mix down to 96. So with my car I got better results both quicker & faster off of 96 versus 95
Thanks again for that. Regarding the gas, I just realized that what I put in was "Trick" gas and rated at 101. So that means I was averaging 97! I went to the track with that and two of my passes were lower than a stock car! And the track/weather conditions were perfect. Maybe 93-95 is the highest tolerance....after that all we get are diminishing returns.
