dmatre

If this is, in fact, true; then either the M276 doesn't REQUIRE 91 octane, or Arrie's lying to us in the post just above yours. No?

Left Coast Geek

if you drive like the proverbial little old lady, never apply even half throttle, not accelerating up steep hills, etc, you might never get into the region where the engine will ping, whereupon, sure, 'regular' low octane gas will be 'ok'. you'd also probably be happier in a 4 cylinder Toyota instead of a high performance Mercedes.

MBNUT1

Explain that given that I think that we agreed that if the engine is not loaded to the point that the knock sensors retard the timing then there will be little if any reduction in mileage. Just to state it 87 has the same fuel heating value as 91.

Arrie

I have no need for lying. Just always wondered why would a DI engine require high octane fuel as fuel-air mixture does not get compressed together like in port injected engine, i.e., there should be no risk for pre-detonation. DI engine works close to the same as diesel other than it still uses spark for ignition but fuel is introduced in the cylinder just at about the time it needs to ignite. So how could it even knock?

Makes me wonder if MB just missed to look at this both in the manual and filler door sticker when changed to DI engines. No, that just could not be possible…right?

Left Coast Geek

Even with DI, the injection and ignition isn't simultaneous, its inject, then ignite.

you don't want the fuel igniting before the spark, and you don't want it igniting anywhere but the center of the head where the plug is. DI engines *can* ping, and the timing is set for high octane gas as that gets you more horses.

my Ford Ecoboost 3.5, which is also DI, the exact same engine in a "Platinum' or Lincoln is 400HP, in my "Limited", its 375 HP. Mine specs 87, the Platinum and Lincoln version specs 92.

pierrejoliat

No, he hasn't compared the mileage yet, he mentioned he didn't notice a performance difference, which is entirely possible, doesn't mean it doesn't exist or it's a good idea to run regular in a car designed for premium fuel

Arrie

I did mention the MPG being exactly the same.

I filled it with 93 octane yesterday and driving it 219 miles today on the same road as yesterday in opposite direction I get 26.4 MPG but I had some traffic jam so I would not call it worse MPG yet but tomorrow I will be driving without traffic on the same highway as on Monday in opposite direction so I will get a better more comparable MPG value.

Left Coast Geek

if you don't enter the operating ranges where pinging would happen, then you will likely get the same MPG.

Chevota

You wont lose 10% mpg, and if you use the mpg the car spits out youre wasting your time.
Yes DI can ping just like a regular car, they are not magically immune.
What octane the car needs and what is ideal will vary, regardless of what the mfg claims is minimum. Plus, gas varies, so 87 from one place can run different than another. If you want to get actual answers you need to data log the ecu and measure the actual amount of gas used. its easy to do and costs maybe $15, then youll know the actusl answer

Arrie

Did you actually read all posts I did in this thread?

Chevota

I skimmed, and read the part where you thought a DI shouldnt ping. Why do you ask?

Arrie

I had already posted the actual MPG based on true miles driven and fuel used.

Chevota

oic, so Im being attacked as if my message was directed at you. The DI ping part was for you, but not the rest, unless you claim 87 reduces mpg 10%. That one is the main reason i replied, then i tossed in other comments while i was in there.

Arrie

Further "trial" added to this same post to keep it together.

Drove my trip back thru the same roads in opposite direction. Started back with the full tank of 93-octane fuel that I filled it up after running the 87-octane fuel empty.
Result is in the below pictures.

There is lots of nay-sayers in this forum about this all, but I am displaying the real values from my drive.

Driving conditions thru all driving was very similar without any wind at all in any direction. The only change was some outside temperature difference.

Why the overall MPG values are so good is because the temperature was cool enough, so the A/C compressor did not run at all. It takes about 15% engine power to run but this trial was not about the total MPG, it was to see if fuel octane makes any difference in MPG in my 2012 S550 CGI engine.

Based on the two days of driving 1200 miles I can say MY CAR gives better highway fuel mileage with 87-octane fuel compared to 93-octane fuel, like it or not. And I also did two very heavy-footed accelerations and the car felt just as strong if not even stronger with the low octane fuel. Did not hear any kind of weird noises from the engine either.

These are true results not doctored in any way. The 93-octane fuel that I started the trip with was from Fast Track, the return trip 93-octane fuel was from some no-name station next to Hampton Inn in Warner Robins, GA. These are not big-name gas stations but when it reads 93-oct on the pump you could assume it is at least something higher than 87, right?

The 87-oct fuel was from the same Shell station both ways in Gulfport, MS at the hwy 49 exit, the one on right side at the light coming from I-10 if someone would be interested in the area. Based on this MPG test this became my favorite gas station going forward when traveling thru the area


Total from fill-up with 93-octane fuel. 21 gal used, gives only 21 MPG true fuel mileage.

Highway MPG value with 93-octane fuel with cruise set to 79 MPH.

Highway MPG value with 87-octane fuel with cruise set to 79 MPH.

This is the values driving from fill-up with 87-octane fuel. Obviously, I cannot calculate the true MPG as I did not run the tank empty, but the MPG value shown is significantly higher than with the 93-oct fuel.

dmatre

Your results are similar to results my father and I got in the 90's in his Caddy with the Northstar V8.

He got 1-2 mpg better with 87 than with 91 octane.

I recall reading that the flame front moves faster across the combustion chamber with lower octane, and goes slower as octane increases. I believe that the article I was reading came to the conclusion that it was beneficial to run the lowest octane fuel which the car did not have problems with. But that was almost 30 years ago, and my memory isn't getting any better....

Arrie

Further "trial".

Drove my trip back thru the same roads in opposite direction. Started back with the full tank of 93-octane fuel that I filled it up after running the 87-octane fuel empty.
Result is in the below pictures.

There is lots of nay-sayers in this forum about this all, but I am displaying the real values from my drive.

Driving conditions thru all driving was very similar without any wind at all in any direction. The only change was some outside temperature difference.

Why the overall MPG values are so good is because the temperature was cool enough, so the A/C compressor did not run at all. It takes about 15% engine power to run but this trial was not about the total MPG, it was to see if fuel octane makes any difference in MPG in my 2012 S550 CGI engine.

Based on the two days of driving 1200 miles I can say MY CAR gives better highway fuel mileage with 87-octane fuel compared to 93-octane fuel, like it or not. And I also did two very heavy-footed accelerations and the car felt just as strong if not even stronger with the low octane fuel. Did not hear any kind of weird noises from the engine either.

These are true results not doctored in any way. The 93-octane fuel that I started the trip with was from Fast Track, the return trip 93-octane fuel was from some no-name station next to Hampton Inn in Warner Robins, GA. These are not big-name gas stations but when it reads 93-oct on the pump you could assume it is at least something higher than 87, right?

The 87-oct fuel was from the same Shell station both ways in Gulfport, MS at the hwy 49 exit, the one on right side at the light coming from I-10 if someone would be interested in the area. Based on this MPG test this became my favorite gas station going forward when traveling thru the area


Total from fill-up with 93-octane fuel. 21 gal used, gives only 21 MPG true fuel mileage.

Highway MPG value with 93-octane fuel with cruise set to 79 MPH.

Highway MPG value with 87-octane fuel with cruise set to 79 MPH.

This is the values driving from fill-up with 87-octane fuel. Obviously, I cannot calculate the true MPG as I did not run the tank empty, but the MPG value shown is significantly higher than with the 93-oct fuel.

BenzV12

Thanks for posting those results Arrie
I said earlier I run premium fuel ,it's not that I'm a fuel snob (if such a thing exists lol ) . I just use premium fuel because turbo engines perform better , accelerates faster from my experience and the difference is dramatic compared to non turbo engines .
I had driven those friggin' Northstar engines , fuel cap said " USE PREMIUM FUEL ONLY' but those cars had come with the knock sensors to compensate lower octane I believe .
When you use premium fuel your mileage also improves ? I thought that way but I have not put it to the test

S-Prihadi

Well, my engine octane rating is European value called RON and is not the same as US MON. US MON while value is lower say 91, its equivalent to RON is higher than 91.
Per my fuel tank door, I am supposed to use 95 RON. I choose to buy 98 RON.
Why 95 RON for a 2014 car was because, in early 1999 to 2016 Indonesia does not have higher than 95 RON unleaded after the leaded fuel gone , only like 2016 and up or so we get 98 RON unleaded.

I use only 2 kind of fuel.
1 is Shell V-Power Nitro Plus 98 RON or 2nd is the government fuel brand called Pertamina, 98 Turbo.
Outside Jakarta, Shell is very very very hard to find. So government fuel brand called Pertamina, 98 Turbo is when I do outside Jakarta run.
My logic is simple. I use 98 RON because if the blending was bad as is "corruption", and a 98 RON becomes a 96 RON from my government fuel brand, I am still safe.

It only cost a bit more money for 98 RON vs 95 RON for my country, like 2.1 USD cents per 1 liter or 8.3 USD cents per US gallon.
So who cares.......

Higher octane is important for my hot climate. Besides our engines have 2 knock sensors which will adapt...up to a limit.
Surely my turbocharged 3.0 is of higher risk if I get lower than 95 RON fuel.

Arrie

But the thing is with the difference between Direct Injection and Port Injection or carbureted engines. DI engine does not compress fuel with air that heats the fuel/air mixture before ignition timing and allows pre-detonation if too low octane fuel is used. In DI fuel enters in cylinder in cold temperature with compressed hot air present and is injected in it essentially at the moment when ignition is to happen so knocking will has much less chance to happen.

It is interesting also when thinking about some comments mentioned that lower octane fuel burns faster or easier. If true this could be the reason why I get results that I got.

I will do some more “trials”.

jmattioni

Interesting thread. Depends on your car and how you use it, but with my SL65 I always use premium (93 min). I'm not worried about gas mileage though it's pretty decent considering. I drive maybe about 3K miles per year in this car.

Also, on the topic of fuel -- where do you buy your gas? For years, I've been using the local convenience store and grocery store gas having bought into the view that "gas is gas and it all comes from the same source". But what I'm learning is that the additives in fuel are as important as the octane. Without those additives your engine builds up carbon and other junk that the additives help clear out.

I recently switched to a name brand gas (Exxon) to see if there's any difference. The immediate effect was that I got a check engine light! LOL My handy diagnostic tool reported that the secondary air system valves were stuck. I managed to free the valves up and clear the code. I continue to use the name brand gas and the problem never returned. My best guess as to what happened is that the name brand gas had more and/or better cleaning agents and they caused a load of built-up contaminants to break loose which clogged the valves. I will continue to use a name brand gas from now on.

If you're in the habit of adding a bottle of cleaning agent to your tank at a fill-up it probably doesn't matter where you get your gas. But I think that probably costs more than just paying a few cents more per gallon for the "better" gas that already has a proper dose of cleaning agents.

The EPA specifies a minimum for additives in gas so even the cheap gas has some additives (probably the minimum). The industry, from what I've read, thinks the EPA set the minimum too low. As a result, there is now a "Top Tier" brand for gas that sets a higher minimum for cleaning agents. All name brand gas meets Top Tier standards from what I could tell on the Top Tier web site. I didn't find any convenience/grocery store gas stations on the list, at least not in my area. Not all but some of the name brand stations will show the Top Tier logo on their pumps.

Chevota

Arrie; I liked the nay-sayer comment. Yes, I am a nay-sayer, or perhaps "the" nay-sayer, and you're still killin me. You still believe DI magically eliminates ping and the dash tells you your real mpg.
What I see in your 90whatver to 87 octane post is; you "think" you got better mpg with 87, the end.
Even measuring actual gas used, like I do, it varies too much tank to tank to make such a claim. I could do the same test, but the only change is the color shirt I wear. If my mpg goes up, which is basically a 50-50 shot because it will be different, it's proof it was the shirt? If I avg the last five tanks compared to the five prior to that, the latter five avg 4.6% better mpg. Maybe I should start documenting what color shirts I'm wearing because it sure as F isn't the gas... I'd imagine it's mostly the air temp, but just a guess. All you can hope for is an inaccurate estimate, just like ever car I've ever owned. Even if you documented mpg for the rest of your life I doubt you could measure the difference caused by 87. And of course you're ignoring the negatives, but like any twin turbo V8 driver you are far more concerned about mpg than anything else. I understand testing just to see what happens, if that was the goal, but the test is still void. Make another ten trips at the same temp on the same tires and lets see if there is a pattern. Exact same stops, same idle time, no differences at all, because any gains from 87 are going to be teeny and even a slight wind change will upset your data. This is lab environment test if I ever saw one.

No you can't hear the ping, see where I previously mentioned data logging. You look for it, not listen. No DI fuel is not cooler, or whatever else you said to justify the claimed magic. The magic that clearly does not exist if you were data log and verify for yourself. I was surprised when I first checked mine, and wondered wth is wrong with this engine? But it's normal, normal to have very retarded timing but still ping, which is the direct opposite of your DI claim.
Data log and see for yourself. Do it on 87 too, and post it, because I'm curious if it pings as you pull out of the driveway.

Imo our cars might as well have a carb on them, and I'd imagine they'd ping less too. At the very least I could get better throttle response and throttle control from it. My truck has a carb, and higher compression, yet it runs about 20 or more degrees advance than my car, and no pinging on 91. When I say that I mean my car with no boost, since the truck has none, to compare the car more fairly. Perhaps it's because the fuel in the truck is cooler. It can run ideal timing, but our cars cannot, hmm....
I wonder what octane we would need to run ideal timing? Guess we'll never know because I don't have access to that much octane. Maybe if it had that miracle DI thing you mentioned I wouldn't need octane Do they make that for an M278? Ok, now I'm poking you with a stick, try not to get too upset, just teasing.

Arrie

A couple of things:

I couldn’t care less about the gas price/savings with the cars I have. If I was worried about that I would drive a Prius.

I’m an engineer who is just curious about this fuel octane rating for the DI engines as it is “set” to the same as with port injected engines but as the engines are so different for the fuel delivery method I’m thinking the required octane rating might be just a bit different regardless what it reads in the filler flap. Easy way for the engine builder to leave octane rating to what it is with port injected as it is the safe way to do it. Does not mean it is the only way.

You are wrong about the fuel temperature. In DI engine fuel entering the cylinder is in a lot cooler temperature at the moment it is sprayed in just a fraction of a millisecond before spark compared to fuel that comes in with suction mixed in air that then heats up during compression stroke. At the time of the spark compressed air/fuel mixture is very hot and fuel octane rating plays an important role to keep fuel ignition under control. Too low octane fuel will lead to ping and engine needs to adjust timing and perhaps amount of air intake for control. DI engine gives much less chance for pinging simply because fuel is not present in the cylinder before it needs to ignite.

You missed the point about the MPG values I displayed. I had values from RESET and START. RESET I use every time I fill up. Then true MPG is calculated from miles driven and gas used.

START during my test is with pure driving, i.e., when I got back on the road on speed I zeroed the START values so it measures just driving MPG and sitting in lights etc. other idle times do not distort the values. This is why the START MPG values are better.

I also mentioned there was no wind during the whole drive in any direction. The biggest difference was with outside air temperature but this was pretty much the same both days during low and high octane runs.

We all have our opinions but my test was not an opinion. It was true values from my car during long highway drive. Yours so far is an opinion, only that.

Go do your own test and be amazed. Sometimes the truth and facts are not what the general opinion is, which so often is “just because it has always been so”.

Chevota

I actually do test, I've data logged my car every moment its been on for nearly two years. Have you logged even once? Check it and you will be amazed, as you say.
My mpg, per the dash, was down ~ 15% today, despite being colder. I'm wearing a blue shirt, will try another color tomorrow DI fuel is hot, Id imagine 200f, then gets hotter after after injection. If my carb fuel was 200 it would have serious issues. Yes it gets hotter in the cyl, so does the DI, which is not immune to that. I know what you're saying, but it simply isnt working out in real life. If it worked like you said then why does it have so much trouble and need such retarded timing to prevent ping? Yesterday for example, I pinged at 2800, zero boost, spark retarded 1.5 less than stock at 11 degrees. Also running 96+ octane. Thats just one example but Ive never seen a car do that and I dont know why. My truck would be 28-32 at that point, and even on 87 it wouldnt ping, because I used 87 often. Just look at the data and see. And, of course, check mpg over months as well.

pierrejoliat

Actually Surya we use RON plus MON divided by two to get our octane number in the US

Chevota

I couldn't help but think of this post when I noted these mpg #'s. The left side is in the AM on my way to work, the right is PM going home that same day.
Since AM was colder, more downhill, and less hotodding and traffic involved, why is my mpg worse?