MB gasoline - regular vs premium

[antonmnster]

I run 87 in my 335i pretty regularly, especially on road trips when premium on the interstate is over $1 more per gallon.

Have 191,000 so far with turbos and DI. The mileage takes 1-3 mpg hit but that's it. No pinging or noticeable performance loss, but I generally use less than half the power the n54 makes.

If the price difference is g, I go for 91 instead of 87.

 

[camrydriver111]

Originally Posted By: antonmnster
I run 87 in my 335i pretty regularly, especially on road trips when premium on the interstate is over $1 more per gallon.

Have 191,000 so far with turbos and DI. The mileage takes 1-3 mpg hit but that's it. No pinging or noticeable performance loss, but I generally use less than half the power the n54 makes.

If the price difference is g, I go for 91 instead of 87.


Interesting, I might give 87 another shot.

 

[edyvw]

Originally Posted By: UG_Passat
Originally Posted By: edyvw
Originally Posted By: MaximaGuy
Concur its not breaking my wallet.
BTW knock and retardation is under load or heavy acceleration and regular driving conditions one never knocks under normal loading.
Curious if the vehicle is designed to only take premium, my Lexus takes regular


Because MB is designed by people using autobahn everyday, while Lexus is designed by people riding train everyday.
Joking on a side (well, still staying behind statement about Lexus), ALL Euro cars require higher octane rating. Europe long time ago decided to use higher octane fuel due to higher compression ratio in their engines.


Europe octane rating is not the same as the US octane rating.

European 91 octane isn't the same as 91 octane in the US.

Due to Research Octane Number vs Anti-Knock Index.

But yes, the highest normal octane available in Europe is 98 RON, which is roughly equivalent to Sunoco 94, which is not available everywhere.

I know it is not. It is different methodology. But, 95 (91 in US) is lowest in Europe (there was long time ago 91 or US 87 in Europe, but that is gone).

 

[edyvw]

Originally Posted By: slacktide_bitog

worth posting this again

European vs US octane sales

type —— US -- European RON
—regular 87 -- 91 (this is not available in Europe)
premium 91 -- 95 usually the lowest grade available in Europe
premium 93 -- 98


I know that, though Europe had 87 or their 91 long time ago. That disappeared with ban of lead in gasoline.

 

[edyvw]

Originally Posted By: antonmnster
I run 87 in my 335i pretty regularly, especially on road trips when premium on the interstate is over $1 more per gallon.

Have 191,000 so far with turbos and DI. The mileage takes 1-3 mpg hit but that's it. No pinging or noticeable performance loss, but I generally use less than half the power the n54 makes.

If the price difference is g, I go for 91 instead of 87.

I must ask: BMW 335i and concern over $1 per gallon?
Geeez.
I can find much cheaper diesel for BMW then Shell, but guess what, DPF regeneration interval with Shell diesel is twice as long then Phillips66 etc.

 

[antonmnster]

I used to drive to Chicago a few times per month. At nearly 1000 miles per trip the dollars added up. Since I was just cruising along at 78 mph under light throttle, I didn't have any regrets.

 

[Tahoe4Life]

Originally Posted By: slacktide_bitog
It's DI. Use premium


I only use 87 regular [Mobil] in my 5.3 DI Tahoe. A friend does Livery in a 2015 DI 5.3 Suburban and uses only 87 octane fuel. He has 180K miles on it and all is well plus he does a ton of idling to keep the Suburban nice and cool in this Miami Beach jungle heat. Everyone I know uses only 87 octane in their DI vehicles with no issues and most of those have way over 100K miles on them.

I really do not think Premium is necessary. Just IMHO but to each their own.

 

[Wrenchman798]

I can tell you as an owner of an Acura, that premium is required, only big difference I can tell is the engine has less power, most noticeable when climbing a big hill or when you need to pass or pull out in traffic. Also using regular 87 causes the MPG to drop 2-4, I have tried this several times and get the same results. So for me in my case using regular cost just as much if not more than using premium due to the loss of MPG. Why? I cannot answer that. If someone can explain why I would love to hear an explanation.

 

[camrydriver111]

Originally Posted By: Wrenchman798
I can tell you as an owner of an Acura, that premium is required, only big difference I can tell is the engine has less power, most noticeable when climbing a big hill or when you need to pass or pull out in traffic. Also using regular 87 causes the MPG to drop 2-4, I have tried this several times and get the same results. So for me in my case using regular cost just as much if not more than using premium due to the loss of MPG. Why? I cannot answer that. If someone can explain why I would love to hear an explanation.


Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.

Where I live premium gas is often ethanol free, while regular contains ethanol. Gasoline has a higher power density than ethanol. I'm not sure how much this contributes but it could be a factor as well.

 

[barryh]

Originally Posted By: camrydriver111

Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.


The description of knock sensor operation is correct but spark timing is always a number of degrees before TDC and never after.

 

[Virtus_Probi]

Originally Posted By: camrydriver111

Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.

Where I live premium gas is often ethanol free, while regular contains ethanol. Gasoline has a higher power density than ethanol. I'm not sure how much this contributes but it could be a factor as well.


This is a good description of the basic concept, but the knock control system for which I designed electronics some time ago was a little more sophisticated than that.
It was a closed loop system that tried to keep the engine on the edge of knock, or even knocking very lightly, whenever it could. The engine guys told us that knocking so lightly that the driver could not sense it was the sweet spot for power and fuel economy. Got to watch a prototype of the system running in a car on a dyno and it was pretty darned impressive.
Haven't really kept up on developments in that field for some time, but I'd imagine knock control is quite a bit more sophisticated now.

 

[Wolf359]

Originally Posted By: barryh
Originally Posted By: camrydriver111

Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.


The description of knock sensor operation is correct but spark timing is always a number of degrees before TDC and never after.


Right, retarded timing means the spark fires so many degrees BEFORE top dead center. If you fire earlier, it generates less power. But if the timing isn't retarded, then there's no advantage to running premium over regular because the BTU content of regular and premium is about the same. BTU content of gasoline is higher than ethanol. Ethanol helps with raising the octane rating but there's only so much you can do with premium so there tends to be a higher cost for premium over regular.

 

[OVERKILL]

Originally Posted By: Wolf359
Originally Posted By: barryh
Originally Posted By: camrydriver111

Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.


The description of knock sensor operation is correct but spark timing is always a number of degrees before TDC and never after.


Right, retarded timing means the spark fires so many degrees BEFORE top dead center. If you fire earlier, it generates less power. But if the timing isn't retarded, then there's no advantage to running premium over regular because the BTU content of regular and premium is about the same. BTU content of gasoline is higher than ethanol. Ethanol helps with raising the octane rating but there's only so much you can do with premium so there tends to be a higher cost for premium over regular.


As camrydriver111 indicated, ignition timing is always in degrees BTDC, advance is the increase in that number, retard is to move that number closer to TDC.

Say for example you are timing an '87 Ford 302. Stock ignition timing, with the SPOUT connector out (base timing) is 10 degrees BTDC. Total advance, SPOUT in, is 28. You are running 91 octane, so you can increase your base timing to 14 or 15 degrees. You put the timing light on, pull the SPOUT, mark the harmonic balancer at the 14 or 15 mark, and you advance the base timing to 14 degrees. This makes total advance now 32 degrees BTDC.

 

[Kestas]

I just read a good article on the push for higher octane gasoline. The automakers claim it'll only cost 3% more than regular, while the engines will get >3% better efficiency. I'm not sure where the automakers get their first figure.

 

[Garak]

They get that figure because they're not setting the prices, so they can simply imagine whatever they want.

 

[bbhero]

I agree 100% Kestas. No way it will be that low a difference. More like 25-30% more if not even higher than that.

 

[Whimsey]

In the past fewer cars called for mid grade or premium fuel. Back then the spread was $.10 & $.20, respectively, more than regular 87 octane. It seems now that with more vehicles requiring higher octane fuel the spread is more like $.30 & $.60. At least where I live in NJ and on the East coast in general as I've seen in my travels. Kind of sounds like economics 101, supply & demand.

Whimsey

 

[MaximaGuy]

Spoke to a friend who had a BMW and he would use 87 gas and it was just fine.
Totally agree the spread on the 87-91 is quite high, I want my vehicle to have one gas for life.
Though I prefer to leave it to learn to live with 87 gas and not change it and confuse the knock points.

 

[PeterPolyol]

Originally Posted By: Virtus_Probi
Originally Posted By: camrydriver111

Normally the air/fuel mixture is ignited by the spark plug when the piston reaches dead center.

When you have an engine knock the mixture is still ignited by the spark plug, however the pressure wave causes a secondary ignition inside the combustion chamber, producing the pinging sound.

When the knock sensor detects a knock, the computer "retards" the spark plug timing so the spark plug fires later when the piston starts moving away. When it does this there is less compression and less power.

Where I live premium gas is often ethanol free, while regular contains ethanol. Gasoline has a higher power density than ethanol. I'm not sure how much this contributes but it could be a factor as well.


This is a good description of the basic concept, but the knock control system for which I designed electronics some time ago was a little more sophisticated than that.
It was a closed loop system that tried to keep the engine on the edge of knock, or even knocking very lightly, whenever it could. The engine guys told us that knocking so lightly that the driver could not sense it was the sweet spot for power and fuel economy. Got to watch a prototype of the system running in a car on a dyno and it was pretty darned impressive.
Haven't really kept up on developments in that field for some time, but I'd imagine knock control is quite a bit more sophisticated now.


Yep. Now they have ion sensing, where the plugs double as an ion sensor. If there is any (or no) combustion happening before plug fires, the ECU will know about it due to the conductivity of combusting fuel. First heard about it on SAABs. Later generations are using the ion current signal to roughly determine the peak cylinder pressure and combustion quality

 

[Tahoe4Life]

Originally Posted By: MaximaGuy
Spoke to a friend who had a BMW and he would use 87 gas and it was just fine.
Totally agree the spread on the 87-91 is quite high, I want my vehicle to have one gas for life.
Though I prefer to leave it to learn to live with 87 gas and not change it and confuse the knock points.


I agree. I only use 87. If the station is out of 87 I will go to a different station. My friend uses nothing but 87 in his 6.2 Yukon Denali XL [over 100K miles] and it runs just fine. He uses mostly Exxon-Mobil.