SufficingMocha

The 2017 E300 owner Manuel states: “only use 95 RON fuel or higher for maximum performance”. I’m very curious about the term maximum performance that Mercedes used there. So has anybody dyno their car to see the performance difference when using the different mixture of fuels? Specially what are the HP differences when using 95 octane fuel instead of 91?

JTK44

There are many threads on this topic: So I suggest you do a search.

Basically, with electronic ignition there is no need nor is there any damage using something less than 95 RON.

Yes there is difference in performance: It is estimated that there is a reduction in horsepower of between 5% and 7% between using regular vs. premium: But keep in mind at 70 mph you are using between 40 and 70 hp to maintain speed. So whether you have 362 HP, as do in my E450 on premium, or 7% less, 336 hp, makes absolutely no difference. You are only using a small fraction of the horsepower available.

What does that 7% loss of HP translates to everyday driving: Nada, nothing. Unless you are drag racing or pulling a trailer you will never notice the loss of horsepower.

As to fuel economy: I have compared fuel economy, by dividing the number of actual miles driven by the gallons taken - not the mileage indicated in the computers in the cars, in my BMW 740i, BMW 740il, BMW 535, Porsche Boxster, Mercedes E350 (6 cylinder) and my E450.. I have yet to see any mileage difference.

There is always a horsepower race between Mercedes, BMW and Audi: so these manufacturers design their engines for maximum horsepower ratings and that requires premium gas.

By using regular the only real difference that you will see is in your pocket: Now unless you own stock in a major oil company, I prefer to keep the savings using regular in my pocket rather than paying extra for premium and giving it to the major oil companies.

Just my $.02

SufficingMocha

Thanks a lot my friend, you definitely saved me from burning my pocket on unnecessary purchases and lot of time by providing this answer. I have done some research on google but I have not seen any answers, nonetheless I appreciate a lot for your effort.

That E450 sounds sweet!

superswiss

I see you are in the USA. North America and Europe use different octane systems. RON is the system used in Europe and AKI is used in the USA. They have different scales. 95 RON is equivalent to 91 AKI, so you have no difference in performance between 95 RON and 91 AKI. 95 RON is mid-grade in Europe. Premium is at least 98 RON which is equivalent to about 93-94 AKI, which is available in some US states. However, the US spec engines are tuned to make max performance at 91 AKI, because it's the least common denominator. Pretty much the entire West Coast and Hawaii only get 91 AKI and California is the biggest US market for automakers, so they tune the cars for California emissions and fuel quality. We also have the benefit to be at sea level in most parts, so we naturally get better performance then somebody living in Denver for example despite turbo charged engines these days. You are likely not getting anymore performance by filling 93 AKI if available, because max performance as said is already guaranteed at 91 AKI. In a pinched it's ok to fill with 87 AKI, but then you will get a performance reduction and with AMGs engine they recommend not to give it full throttle if using 87.

SufficingMocha

I see, AKI does ring a bell and I must have mixed it up with what was on the owner Manuel. And indeed, I lived in California and I have been mixing 100 octane fuels with 91 octane to get 95 aki mixtures which if I understood correctly. Thanks for clearing things out!

SufficingMocha

But since US version engines are tuned to capped with 91 AKI fuels, then I guess an ECU tune probably would eliminate this problem for good?

superswiss

Yes many aftermarket tunes take advantage of higher octane fuels. They usually come with multiple maps, so you can activate the map that gives you the best performance for the grade of fuel that's available in your area. Many of the aftermarket tunes don't provide a whole lot more power on 91 AKI. To really get the power they promise you have to use at least 93 AKI and switch to the 93 map.

SufficingMocha

Great, thank you!

The G Man

Going from 91 to 95 octane might not be worth while, the ecu will not be able to take too much advantage of the 95 fuel. However, I would use 87 octane in emergency situation only, unless you dont plan on keeping your car long term. The ecu compensate for the 87 octane by pulling back timing once the knock sensor detects knocking, even before the human ear picks it up. Once the timing retards and the inaudible knocking stops, the ecu will start to advance the timing again as it was programmed from the factory. This cycle repeats itself for as long as you have 87 octane in the tank. Over time, this could cause incomplete combustion, hot spots and carbon build up,

JTK44

The timing will only retard to prevent pre-detonation upon hard acceleration: As I posted if you plan to drag race your Mercedes from a stop sign or pull a trailer then use premium. If you drive normally you will be fine with regular.

Remember premium is "recommended" not mandated and by recommended Mercedes means for full performance: to be able to use all available horsepower.

In nearly 30,000 miles I have never floored my E450 from a stop sign and very rarely floor it while driving or passing. I drive "defensively", keep space between myself and the car in front of me and do not accelerate hard or drive agressively.

Before you ask, I choose the E450 over the E300 because of the smoothness and quiet of the 6 over the 4 in the E300. At highway speeds the E450 is quiet and smooth as silk a luxury car.

The G Man

The timing, even at low speed, the timing is longer due to 91 octane’s higher ignition pressure rating which means more advance timing. Knock sensor determines how much to retard the timing when using 87 octane.
From the owner’s manual, “ As a temporary measure, if the recommended fuel is not available, you may also refuel with unleaded regular gasoline with at least 87 AKI,”
In my opinion, high compression forced induction, direct injection engines requies the proper fuel. I use to say to people, don’t cheap out on the gas but that is not the case anymore with the high price of gas.

JTK44

Actually the higher octane prevents pre-detonation. Octane rating is a measure of the fuels ability to resist pre-detonation.

Mercedes are sold world wide with great variance in the availability of fuel: therefore the engines and electronic ignition systems are designed and built to accommodate a wide range of fuels.

As to why Mercedes recommends premium fuel, see post #2 and #10 above: this is meet performance standards: 0-60 times and horsepower ratings.Nothing to with longevity or damage to the engine.

For example in Colorado the highest octane rating I have seen is 88. Mercedes and all other cars run just fine on 88 octane rating.

The G Man

Also, babying an engine is not always the best thing you could do for your car. A babied engine and engine using cheap gas is a dirty engine and an engine that runs at high rpm once a while and using recommended fuel type makes for a cleaner engine.

superswiss

Where in Colorado is this? Just curious. Colorado's highest octane is 91 like California. That's premium. However, Colorado uses lower octane for regular and mid-grade. Regular is 85 and mid-grade is 87. Normally 87 is regular and mid-grade is 89.

JTK44

Sorry to disagree and hopefully last comment:

Normal driving, without flooring it is not babying a car: Flooring the car from a stop light puts stress and wear and tear on the engine, suspension and transmission. It is a myth and wife's tale that your car needs to be run periodically at high rpm to "clean out the engine": Use the UPS driver for an example: they get rewarded for safe driving.

I am surprised that you do not know that regardless of octane rating the same and/or similar detergents are used by all major brands of gas. It is a myth and wife's tale that higher octane gas runs cleaner than regular. In fact regular, mid level and premium all provide the same amount of thermal energy.

see: https://www.google.com/search?q=whic...hrome&ie=UTF-8

JTK44

Steamboat, Vail, Eagle all towns at high altitude

superswiss

Yes, you can get away with lower octane at high altitude. The altitude is a much bigger factor in performance than octane at that point, even with turbo engines.

The G Man

no one is talking about flooring your car at every green light but if your car never exceeds 3000 rpm, you are babying it too much and will actually do more harm than good. Also, your engine needs to get hot once a while for a extended period of time to burn off the condensate from your engine oil.
Yes all gas of the same brand have the same detergents but that has nothing to do with octane or timing.

The G Man

That is one of the reason why turbo engines are so desirable at high altitudes. Turbo charging an engines at high elevation is an efficient way to minimize horsepower loss due to high elevation and lower atmospheric pressure.

JTK44

Yes many years ago, especially if you owned a Ferrari: No longer true. If redlining your car gives you satisfaction and jollies then by all means do it, but it is completely unnecessary in a modern car.

If you drive 15/20 minutes your engine will be at operating temperatures: 250 degrees F..

The G Man

Again, no one is taking about red lining the engine, its more about engine temp. More specifically, oil temp. if you drive 15 mins, your car will be warmed up, another 5 mins or so for the oil temp to come up to operating range, need another 30 minutes or so to burn off condensate in oil. Total about 50 min drive at least once a week or simply change your oil on shorter time interval. If you increase the rpm a bit, put it in sports mode, your oil temp will come up faster.