Ramsino

I understand how octane works but I am not sure if my stock 2020 C43 would reap any benefits from higher octane. I live in California and can only get 91 octane from the pump. If I were to travel to other states that have 93 octane, can I fill up with this and actually notice a positive improvement in performance?

With other cars that I have owned, I can find resources that say that there will be no performance gains since the car was tuned specifically for that octane rating. However, I know the C43 can run higher octane, stock, in other countries. Does anyone know for a fact or can point me somewhere that states what the C43 is tuned for? It doesn't make sense to me that Mercedes would tune the car for 91 octane for California and some other states in the US. I'm sure they just tune it for 1 octane and rely on the ECU to adjust for the rest (if it's not too far off).

Is the C43 actually tuned for 93 octane from the factory and it just happens to be "okay" with 91 octane, but that's not the optimal octane for the car?

Trekt43

The car will adjust for a better octane in that it may improve its timing, but a better way to think of this is that it will un-reduce its timing. The car keeps track of your average octane rating over time as well as its best guess at your current octane, based off pre-knock detection. You will most likely not notice any significant performance gains using a higher octane without a tune, unless, your performance is currently reduced due to lower octane, or perhaps a very warm day. The car will improve its performance up to its ideal stock-tuned amount and pretty much stop there.

Ramsino

Do we know what the stock tuned octane for the C43 is? I would think it's 93, but not sure.

Trekt43

I believe you need to think of it more in terms of the car is designed to make certain power given a combination of boost, timing, throttle, etc. given certain external factors such as temperature, octane, density etc. The car is designed to make that power safely given reasonable conditions on 91 octane. You might hit that power more often in less than ideal conditions using a higher octane, but it won’t be noticeable.

19’43s

@Ramsino yes the car does pick up on 93/94 octane as on the fuel handle it says 91 minimum so the cars ecu automatically adjusts and you may have like 10-15 whp more w 93+ octane then 91

superswiss

First off US spec cars are tuned for full power at 91 octane. I did European Delivery, and the ECU was tuned for the higher octane ratings in Europe. 91 if you convert it to the European RON is only about mid grade. Once the car arrived stateside, the VPC reprogrammed the ECU for 91 US octane. Contrary to what some people may think, the ECU can't actually measure the octane of your fuel. Instead it starts to retard ignition timing if it detects knock. If no knock is detect, then the timing is as optimal as it gets. The ECU is tuned to not knock with 91, so it has no reason to advance the timing if you fill it with 93 or higher. It only retards the timing if you fill it with 87 or 89 and it starts knocking. Generally knocking occurs under high engine loads, that's why if for some reason you can't fill with at least 91 the manufacturer may recommend not to use WOT and don't drive the car hard until you can fill up with at least 91 again. For example this is the case with the C63 and specifically stated in the owner's manual.

BTW, higher octane is not necessarily better, because octane indicates how easy the fuel is to combust. Higher octane means it's harder to get it to combust.

1Gunner

I have run 94 in my wife's 2020 C43 both before and after tuning with JB4 without issue.

19’43s

@1Gunner ive been putting 94 since the day I got it, @ the guy who’s talking about 91 being the best, it says 91 minimum on it lol don’t you guys realize that turbo cars love high octane fuels, the higher the octane the better essentially but if it’s stock then tbh you can put 93 and it should work at its peak on stock everything and a little 10% ethanol ain’t never hurt nobody it burns cleaner and works as a octane booster , 94 is a little overkill but in Canada petro Canada has 94 and its readily available so good for us I guess ? lol it’s a nice Benz w turbos on it treat it well now if you’ve already spent a a **** ton of money buying it, maintain it

superswiss

I must respectfully disagree. You might be referring to me here. As I said above, the goal here is to have a combustion w/o knock. At 91 octane, there should be a knock free combustion if your engine is healthy, so increasing the octane really doesn't do anything, unless for some reason your ECU decided to retard the ignition timing with 91, but then I would say there's an issue with your engine. However, a lower octane rating can lower your mpg. Knock occurs in the combustion chamber if the temperature gets too high. This is particularly likely with turbo charged engines, because the compressed intake air is hotter. To combat that, they inject a rich fuel mixture. The fuel as it evaporates has a cooling effect and brings down the temperature in the combustion chamber. With higher octane rating the temps can be higher before the fuel self combusts, so there is less need of a rich fuel mixture and hence less fuel is consumed. This is why many say trying to cheap out by filling with 87 or 89 while the ECU will adapt results in lower mpg and essentially wiping out most of the savings of filling with cheaper fuel. There's no harm putting in 93 or 94 if that's what goes for premium in your neck of the woods, but the car won't make more power than on 91, unless you run an aftermarket tune for one of the higher octane ratings. The same goes for cars that only require 87 or 89 minimum. Filling them with premium is a waste of money.

DLAMG_1979

Lucky for us all, someone tested this theory: https://www.caranddriver.com/feature...dodge-charger/

And yes, octane made a difference.

PortC43

I ONLY use 93 and up octane since day one ! Had my C43 for 2.5 years no issues whatsoever !

gg_monogram

NYC here we only have 93 > 89 > 87

19’43s

Dude your spitting text book facts but tbh the shifts and the car feels smoother and wayyy faster w higher octane so that’s not gonna stop me from putting the best for my amg

GuardianVA

You're both right (or wrong, depending on perspective). The ECU in these cars has a max timing advance in the stock tables. 32* at WOT I believe, but don't quote me. What timing you actually get is first dictated by IAT, not octane rating. So at the same IAT, 91 and 93 (hell, even 104) is going try for the max target in the table, adjust down for the seen IAT, add it's fuel, and there it goes. So at higher intake temps, higher octane isn't always going to make more power, just because the timing target is going to end up lower than what 91 or 93 could support. However, if the intake temperature is below a certain point, 93 will give more power than 91. A tune changes all of that, as it adjusts up targets across the table. A separate component is the difference between ACN 91 in Cali and many 93 offerings, is the amount of additives and the wildly inconsistent Ethanol levels in Cali 91. Higher octane isn't always going to give more power as an end result...there will be other factors that will go into it.

superswiss

Yeah, I didn't feel like getting into the nuisances. My simple point that you are doing a better job at explaining was that if you are already getting max possible timing advance with 91, 93 or 94 isn't gonna give you more, but there are certainly situations where it could. IAT is a whole other factor by itself. Colder air is denser and packs more oxygen, so more fuel can be burned, hence more power. I would say across the board on average you'd be hard pressed to see more power with 93 unless you live in really favorable climate. We can also add altitude to the mix, although not as big of a factor with turbo charged engines as with naturally aspirated engines, but here in Cali I'm at sea level, so I have quite an advantage over somebody in Denver for example, even if they are running 93. I can say this much. My C63S feels faster here with AKI 91, than it did in Europe with RON 100 at averge 1200 feet or so.

Ramsino

I live in Cali too. I thought all cars are tuned up a bit when ever they are sold to a buyer in Cali because we have to deal with the fact that 50% of the cars on the road are Teslas and the $50k Tesla gives us a run for our money. So the cars we get come from the factory tuned all the way up to compensate for this. I don't think it has anything to do with our AKI 91 vs Europe's RON 100 or whatever.

gpouliniii

In high compression engines like ours, higher octane is always better, burns cleaner, which creates more power and better gas mileage while doing it. My girlfriend was told she could use 89 by some idiot because he had a Honda and those cars run no different on any octane because the Japs know how to build an engine better than anyone, they just don’t make their cars luxurious like MB does. Needless to say her car started running like one of the coil packs were unplugged and like it had a serious miss in it. I couldn’t figure out what was going on with it and then she finally asked me if the gas would matter lol. They say the more things cost, the better it is. I don’t think that’s the case with everything, but when it comes to you’re car, it is.

Does anyone know when the price difference started went from being .10 higher per option to .30 more per option? Lol. The gas here in Cincinnati Ohio is $2.09-89 octane $2.39-91 $2.69-93. It used to be in .10 increments years ago, but after driving a Honda for 9 years, I never really paid attention because I only had to run the cheapest octane in it lol.

White One

C450 AMG here...The ECU will adjust timing to the signal from the Knock sensors..No knock = more timing..More octane = less knock and more timing available which gives more performance. That is how it was explained to me years ago...The 91 recommendation is probably based on wide availability..Detonation or "knock" is an engine killer.

White One

The components used to produce octane in gasoline are more expensive to produce, ship and blend..The gasoline business isn't very healthy right now, and octane increases aren't cheap..There are mandated limits on aromatic content in gasoline, varying from state to state, country to country..This historically has been the "cheapest" octane source available for blending. At this point there is more competition for these components, therefore the price goes up.

19’43s

@White One yessir let em know