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Outstanding Contributor
1990 500SL, 1986 500SEC
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1,799 Posts
Discussion Starter #1
Anyone else run this, ever? Any reason to, or not to?

I put about a half tank in this morning, seems to have helped a slight idle lumpiness. It was never enough to show on the tach but it could be felt, now it feels slightly less (or is it just my wallet that has diminished?)
 

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1988 560SL (California Model)
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5,104 Posts
In Vegas we have 100 octane at some Rebel stations. Usually about 6-8 bucks a gallon. Would have to admit it's tempting to try it. If I did I would probably temporarily remove the little timing resistor (retards timing) under the hood. Can't imagine any pinging with that high of octane.
 

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560SEC / 850CSI / 525i
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73 Posts
Ive read that no US spec W126 came with Knock sensors, so there cant really be any benefit in putting such high octane in such an old, low compression engine. Higher Octane = lower calorific value. If you arent gaining efficiency via Timing adjustment, then its a net loss.
 

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Outstanding Contributor
1990 500SL, 1986 500SEC
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1,799 Posts
Discussion Starter #4
Ive read that no US spec W126 came with Knock sensors, so there cant really be any benefit in putting such high octane in such an old, low compression engine. Higher Octane = lower calorific value. If you arent gaining efficiency via Timing adjustment, then its a net loss.
Thanks! I should have mentioned that I am putting it in a Euro spec 560 10:1 compression with electrically adjustable timing.

Still trying to get a handle on the adjustment dials and how to use them properly though.

Here is what I have found so far (quoting a post from Bondavi I believe):

"The EZL dial - what's the best numerical setting to retard timing for optimal smog numbers - I have mine apparently at the premium performance setting of "1".

UPDATE: Answered my question w/ a search:

Nr. 1 = Open circuit | 0 degree retard | 92+ Octane
Nr. 2 = 2.4 kOhm | 2 degree retard | 90-91 ?
Nr. 3 = 1.3 kOhm | 4 degree retard | 88-89 ?
Nr. 4 = 750 Ohm <- "S" | 6 degree retard | 87-89 ? (possible 85 - NOT RECOMMENDED, SEE OWNERS MANUAL)
Nr. 5 = 470 Ohm | 8 degree retard | Unknown
Nr. 6 = 220 Ohm <- "N" | 10 degree retard | Unknown
Nr. 7 = 0 Ohm | 12 degree retard | Unknown"
 

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560SEC / 850CSI / 525i
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73 Posts
Hmm, good info, I have the same setup. Bit sad none of the settings advances timing at all though! Presume the top notch is the "set" position marker?

EDIT: Why is S (Super Unleaded) not recommended? I found an alternative guide on Peachparts forum, contradicts the above. Ill have to check my units markings in the morning, the numbers replaced by letters is diff to the above.

SWITCH: RESISTANCE: RETARD: OCTANE:
S infinite 0 degrees 98
2 2400 ohms 2 95
N 1300 ohms 4 93
4 750 6 91 (the US setting)
5 470 8 89
6 220 10 87
7 0 12??? ???
 

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96 and 08 911 turbos
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2,988 Posts
dicking around with the timing without a knock sensor, dyno, or EGT gauge is dangerous business.

That said, if the adjuster you are using does not offer any advance past 91/93 octane, and you aren't currently getting detonation, then the 100 octane offers no advantage, and actually will likely cause you to lose power.

The important thing here is to determine if you are getting detonation or pre-ignition.
 
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