220S

Just to add more confusion, the minimum is 93 RON octane rating, not 93 AKI octane rating. The minimum AKI octane for these cars is 91. The USA uses AKI (anti-knock index) and most of the rest of the world uses RON (research octane number.)

The E63 (same motor) owner's manual says:

"Only use premium unleaded gasoline. The
octane number (posted at the pump) must be
91 min. It is an average of both the Research
Octane Number (RON) and the Motor Octane
Number (MON): (RON+MON)/2. This is also
known as the ANTI-KNOCK INDEX.
Reformulated gasolines (RFG) and/or
unleaded gasoline containing oxygenates
such as ethanol, TAME, ETBE, IPA, IBA, and
TBA can be used provided the ratio of any one
of these oxygenates to gasoline does not
exceed 10%; MTBE must not exceed 15%."

In Germany there is: "Normal" 91 RON, "Super" 95 RON and "Super Plus" 98 RON. 95 RON is the equivalent of 90-91 AKI (in the USA.)

In Europe "Super" (95 RON) is "premium" for the AMG motors. That's closer to 91 AKI in the US.

My car says minimum 93 RON on the tank filler door. And 91 AKI doesn't cause me any knocking (fwiw, I use 'top tier' gas like Chevron and add some extra Techron once in a while.)

MBH motorsports

+1

If I may add, You never see the letters "AKI" printed on the pumps. Instead you see this "(R+M)/2)" In turn that means "AKI". Or an other way to put it is they take the RON # and average it with the MON #. So when you see 91 or 93 octane in the USA. That is an averaged number from the RON # and the MON #

I always like to know what the MON number is a race fuels. I was having a conversation with the fuel guy at the local strip about a year ago. His Torco 100 octane had a MON # of 100. where as his 110 octane had a MON number if 104. Is this true for all race fuel? I have know idea

One last tid-bit: My C55 ran 100 octane very day. Its all I put in. I could only use like 3 gas stations in my area. Most of my driving revolved around being close to those stations. One station I used kicked butt. It was great fuel. Then all of a sudden the other station I used caused my C55 to pull timing. The used (or said they used VP street Blaze). I learned to stay away fromt hat station after myself and a few other seen bad things happen on the dyno. We all got our race fuel from that station. I dont think it was VP Street Blaze fuel that caused the issue. I think it was some other brand they were selling as VP.

If I had to make a call for the best race fuel, I would say Sunoco is were its all for me. never an issue for me on m very aggressive race map.

E55AMG99

The variances in Octane numbers on race fuels is usually because of the difference in testing fuels over 100 octane. Remember that Octane the hydrocarbon has an octane rating of 100. MON and RON numbers are generated on a single cyl test engine with variable compression. The fuel being tested is compared to a blend of Octane and Heptane which has an octane rating of 0. The ratio of these two hydrocarbons is varied until it matches the anti-knock properties of the fuel being tested. If that ratio is 5% Heptane and 95% Octane, the octane rating is 95. MON and RON values are generated by running the test under two different conditons. Since pure Octane is only 100, the test for fuels over 100 is run to guage power increase instead of resistance to knock. They use a supercharged engine with variable timing. If power output increaese 10% then the octane rating is 110. So, it is possible for one fuel to have MON of 100 or less generated using the knock test on the standard single cyl engine and RON of 101 and higher generated using the power test superchaged engine. Unfortuantely, there is no standard for race fuels. BTW, over 100 and they call it Performance Number instead of Octane Rating just to add to the confusion.

Forgot to add that another thing that causes the difference is the chemical make-up of the fuel. Not all 110 RON fuel will have the same MON. Depending on the package, the Sensativity (difference between RON and MON) will vary greatly.

SonnyakaPig

I was hoping someone was going to read my post carefully and correct that sentence if it was wrong. haha

Thank you for the correction. And also for the great and detailed information. I'm going to review what you wrote for future reference.

Btw, I use only Shell and Chevron. But even with them, I have gotten bad batches of gas. I noticed it more when I had a F/I car some months back.

SonnyakaPig

I also like Sunoco 100 octane. Fortunately, they sell it at the pump about 20 mins from me.

AgSilver

And now we have 102 RON available in Germany.

Also, the six port SLR injectors will provide a noticeable improvement.

I still recommend regular doses of Techron concentrate. It will absolutely eliminate carbon buildup, a major cause of pre-ignition.

That said, it seems to me that the motor electronics of the 113's and the motors themselves are remarkably robust considering the limits they have been taken to and how infrequently (if ever) they experience catastrophic failures.

Oh and if you want to play with numbers, here's a good url:

http://www.wallaceracing.com/Calculators.htm

Benz-O-Rama

All this octane talk persuaded me into putting a few gallons in the SL600, that has a OE Tuning, 93 octane box tune.

Car had roughly a 1/4 tank of 93 octane in her when I pulled up to the Sunoco 100 pump. I added 5 gallons ($30.00 cha-ching) of the 100 and added 5 more gallons of 93. Hell if I know what octane I ended up at, but the car certainly felt stronger on the way home. Placebo? Possibly. But once I got out of the rinky-dink town the pump is in, and on the highway (6 miles or so), I opened her up and the car felt super strong on full boost. It should also be noted that many of our roads have pre-treatment chemicals still on them, from a snow storm that never came. That could be another reason why I was breaking traction at 60+ MPH.

Anyway, with the uber cold weather we've been having, it's never a bad idea to add some octane for detonation insurance.

I'll probably try it again for our next MIR rental.

LZH

Here's and example of the equation for mixing octane - it's very simple.

100 (octane) x 5 gal = 500
93 (octane) x 10gal = 930

(930 + 500) / 15 (total gallons) = 95.3 octane

Benz-O-Rama

Didn't realize it was that simple, thanks. I thought for sure there would be some complicated formula to figuring it out.

AgSilver

We pay that much for regular here in Germany and about $8/gal for 102 RON or about $150 to fill the E55, but it's worth it - - - super smooth roads and no rim-cracker potholes. It's always a kick to pull up on the police at 140+ and have them move over for you. No where else on the planet can you do that.

cal1

I'm glad you brought up the notion of a bit of no-knock insurance. Putting the performance discussion aside, doesn't it make sense to run a mix of higher octane on track days for that reason alone?

LZH

AFAIK warmer ambient temps increase the chance of detonation/knock...not cooler temps. Colder temps actually decrease the chance knock.

Benz-O-Rama

Yeah, you're right. Colder intake temps should help decrease knock.

I was thinking more along the lines of a car being tuned at say 80* ambient, with an increase in timing. Not a huge problem since these cars will retard timing as IATs increase. But, as ambient drops below freezing, IATs will also drop, causing a decrease in timing retardation, increasing your chances of
something bad happening. Running a bit higher octane in that circumstance will help combat that, no?

MRAMG1

Gentlemen:

I have ALWAYS run a little extra octane for ANY track event. Road race/autocross/drag.

YES your car may not need it, and YES it could actually cut down on performance a little as the higher octane gas USUALLY burns slower. But it is cheap insurance and I have NEVER had an engine let go on me at the track in over 20 years of racing.

I usually just use a can of 104 black label, and have found via track running, mainly road racing, that it is as good as 5 gallons of turbo blue, 110 octane.

Again, I ONLY use it for insurance, and mainly in my old Supercharged stang.

I have used it in my old C32 for road days, and in the S600 for draggin. It was simply nice to know that regardless of the weather conditions, aka high humidity or temps, it was in there

Arrie

Yeah, and the polizei in Germany really moves over too.

Here in US they don't and if you get close enough then they will just to let you pass and then come with the blues on and give you a ticket for tail gating.

Quadcammer

folks, this doesn't make sense.

what you all are suggesting is that the car is seeing knock retard on 93 octane. In other words, the knock sensors are active using the highest octane fuel that you can regularly purchase in the U.S. and likely europe as well. Given how OEMs are concerned with longevity, that would not make much if any sense to have a car even close to detonation on 93. Maybe on 91...maybe.

The ECU and motor in the 211 is nothing fancy. It has no clue what octane is in the car. All it knows is whether the car is detonating or not. If the car doesn't detonate on 93 (which I'm pretty sure it doesn't), then 95 octane or above is a waste of money.

Furthermore, remember that race fuel has a different stoichometric a/f ratio than standard gasoline, which can cause further havoc to the vehicle's performance.

In my opinion, people who say the car is faster or "makes more noise" are experiencing the wonder of a placebo effect. Like that imaginary 5rwhp gain is gonna make the car louder.

come on now folks...if you want to pay $7/gallon for race fuel, do so at your leisure, but don't think you are gaining much if any performance.

Quadcammer

What you're saying makes no sense.

As you correctly note, the car will retard the timing as the IATs increase. Hence, it will feed in more timing as the temps get cooler. But this is not for some arbitrary reason. The car is less likely to detonate at cooler IATs, hence it can handle more timing.

There is no need for additional octane here.

skratch77

Stock car aside...a modded e55 in the summer will trap higher on race than pump.tried it my self at the 1/4 and picked up 2 mph that day.

Oliverk you do know in star that you can set the car up for 91 and 93 base oct right?

Quadcammer

then that modified e55 in the summer is pulling timing from the knock sensors. Log the run and you'll see the knock sensors active.


Yes, you can set it up for 91 or 93...notice how there is no 95 octane option.

Those two options will have different timing maps. But that will be the commanded timing in WOT open loop. The computer is not going to add in more timing than the value commanded here because the car assumes thats what fuel you're using. IF the knock sensors aren't active on 93, it won't know that you're running 95 or 105.

skratch77

E55s pull timing big time in the summer and most of us with tunes will take advantage of the extra knock protection.

I know how it works bud iv dynoed and tweaked my own car.even stock 55s with 93 will still pull timing and you will notice 100oct all day

Quadcammer

so what you're saying is that Mercedes has designed a car that will detonate all day long with the factory tune and gets the joy of having its power ripped out by a knock sensor that constantly active.

That would be pretty dumb, but I guess MB does do some dumb stuff.

skratch77

Do you have an e55?our supercharger setup is known for not being efficient and on boost the temps skyrocket real fast.

80 out and one quick wot to 130 and the intake temps are over 140 and the car dumps fuel and pulls timing.

Heat is a huge issue with our platform.

Quadcammer

no I sure don't, although I have first hand experience with an SL55.

Then again, if the car is pulling timing solely due to high IATs, then knock sensors would be irrelevant, and fuel type would again not matter.

I guess this brings up the question:

Does the car pull timing if IATs are high, even if the knock sensors are not active?

If it does, then fuel type doesn't matter.

AgSilver

In Star DAS there is a test for the "knocking tendency of engine." The possible causes listed are in the following order: "poor fuel" "carbon deposits." Nothing said about high IAT's. I suspect when the IAT gets to a specified limit the ECU shuts down the supercharger as is the case when the IC pump fails. Why should it be any different than any other modern engine?

There are certainly limits to the advance curve regardless of fuel, but with the adaptive ability of the ECU, a few WOT, high rpm runs should get you pretty close to best power for current conditions whether you have a stock or modified ECU.

cal1

It seems like poor fuel and carbon deposits are ever present posibilities. Given this, doesn't running a bit of unleaded race fuel when you plan to push the motor make sense or is it truly not worth the extra cost of the fuel?