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  #76  
Old 09-14-2018, 02:05 PM
Michael Schott Michael Schott is offline
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Originally Posted by Alien007 View Post
AKI?
We're talking about fuel bro.
We are talking about how an ECU is programmed. Thatís the only reason an engine may need higher octane fuel. Itís ultimately about compression ratio and potential for detonation.
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  #77  
Old 09-14-2018, 02:35 PM
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Driving environment, spark plug type...air intake flow...it's all set to work with premium best that's why they write premium on it. They design their models to be able to do extended driving at high speed...like on THEIR highways. A lower octane can run a bit too lean at higher speed...likely aren't going to feel that but spark plugs won't last as long.
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  #78  
Old 09-14-2018, 02:48 PM
Closem Joe Closem Joe is online now
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Originally Posted by Elk View Post
But again there are those who would prefer not to spend money they do not have to - regardless of how trivial that amount may appear to others.
Elk, location not known, if you buy a top of the line car with an engine that runs like a fine watch, why would you even think about getting a lower grade gas to save a few bucks. Really!

Joe
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  #79  
Old 09-14-2018, 02:54 PM
Alien007 Alien007 is offline
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Trying to save the money could very well lead to costing you in the long run...I don't have the inclination to argue against the technical recommendations from the builders of their own high tech award winning engines.
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  #80  
Old 09-14-2018, 06:36 PM
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Originally Posted by Closem Joe View Post
if you buy a top of the line car with an engine that runs like a fine watch
This thread is about a stock F30 320i with N20 engine. "Top of the line car with an engine that runs like a fine watch"? HAHA
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  #81  
Old 09-14-2018, 08:33 PM
Autoputzer Autoputzer is offline
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Forced induction (turbocharging or supercharging) will increase the octane requirement. Detonation occurs when the fuel-air mixture is prematurely ignited by a source of heat inside the combustion chamber other than the sparkplug. Pistons, valves, and occasionally the cylinder head will develop hot spots that are hot enough to ignite the fuel-air mixture. The audible pinging is the result of two flame fronts colliding, one originating from a hot spot and one from the sparkplug, or two fronts originating from hot spots.

Compressing the intake air (forced induction) also heats it. An intercooler will remove some of the added energy (heat) from the compressed intake air, but not all of it. With more air (and hotter air) and fuel crammed into the combustion chamber with each intake stroke, the combustion temperature will be higher than in a naturally aspirated engine of the same size but less output. That will leave the pistons, valves, and cylinder heads hotter, and therefore more prone to developing hot spots and pinging.

Last edited by Autoputzer; 09-14-2018 at 08:43 PM.
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  #82  
Old 09-15-2018, 06:23 AM
Michael Schott Michael Schott is offline
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Originally Posted by Autoputzer View Post
Forced induction (turbocharging or supercharging) will increase the octane requirement. Detonation occurs when the fuel-air mixture is prematurely ignited by a source of heat inside the combustion chamber other than the sparkplug. Pistons, valves, and occasionally the cylinder head will develop hot spots that are hot enough to ignite the fuel-air mixture. The audible pinging is the result of two flame fronts colliding, one originating from a hot spot and one from the sparkplug, or two fronts originating from hot spots.

Compressing the intake air (forced induction) also heats it. An intercooler will remove some of the added energy (heat) from the compressed intake air, but not all of it. With more air (and hotter air) and fuel crammed into the combustion chamber with each intake stroke, the combustion temperature will be higher than in a naturally aspirated engine of the same size but less output. That will leave the pistons, valves, and cylinder heads hotter, and therefore more prone to developing hot spots and pinging.
Then why are there turbo engines that run fine on 87 octane fuel? Most modern turbo engines use intercoolers already. Technically forced induction can be the reason for higher octane fuel but it's more than just that.

It's a complex combination of compression ratio, boost pressure and engine computer management that determine and engine's resistance to detonation thus octane requirement. Most turbo engines are tuned to get the most power and probably even more important to the manufacturers, fuel efficiency. This determines the amount of spark advance. Reduce the spark advance and you can use fuel with less octane. This reduces power and efficiency.

Last edited by Michael Schott; 09-15-2018 at 06:27 AM.
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  #83  
Old 09-15-2018, 06:34 AM
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Originally Posted by gkr778 View Post
This thread is about a stock F30 320i with N20 engine. "Top of the line car with an engine that runs like a fine watch"? HAHA
No 320 for me. i was referring to my new 440 vert. with the fabulous, smooth running turbo six.

Joe
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  #84  
Old 09-15-2018, 09:19 AM
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Originally Posted by michael schott View Post
then why are there turbo engines that run fine on 87 octane fuel? Most modern turbo engines use intercoolers already. Technically forced induction can be the reason for higher octane fuel but it's more than just that.

It's a complex combination of compression ratio, boost pressure and engine computer management that determine and engine's resistance to detonation thus octane requirement. Most turbo engines are tuned to get the most power and probably even more important to the manufacturers, fuel efficiency. This determines the amount of spark advance. Reduce the spark advance and you can use fuel with less octane. This reduces power and efficiency.
+1
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  #85  
Old 09-15-2018, 10:31 AM
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Originally Posted by Alien007 View Post
Driving environment, spark plug type...air intake flow...it's all set to work with premium best that's why they write premium on it. They design their models to be able to do extended driving at high speed...like on THEIR highways. A lower octane can run a bit too lean at higher speed...likely aren't going to feel that but spark plugs won't last as long.
ECU software is designed for the US market not Europe.
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  #86  
Old 09-15-2018, 10:49 AM
Autoputzer Autoputzer is offline
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Originally Posted by Michael Schott View Post
Then why are there turbo engines that run fine on 87 octane fuel? Most modern turbo engines use intercoolers already. Technically forced induction can be the reason for higher octane fuel but it's more than just that.

It's a complex combination of compression ratio, boost pressure and engine computer management that determine and engine's resistance to detonation thus octane requirement. Most turbo engines are tuned to get the most power and probably even more important to the manufacturers, fuel efficiency. This determines the amount of spark advance. Reduce the spark advance and you can use fuel with less octane. This reduces power and efficiency.
Those have relatively low-pressure turbocharging, and they are tuned (de-tuned) to run on regular gas. A lot of car buyers would balk at buying a car that requires premium gas. (Similarly, a lot of car buyers would balk at buying a car that requires synthetic oil.)

Higher efficiency and higher power output is achieved by generating a hotter flame temperature, and that causes hot spots, and that causes pinging.

Even BMW de-tunes their engines to run on 91 AKI, since that's highest AKI readily available in a lot of areas. That's why all those software tuning products work. They make more torque and power, but they often need higher AKI fuel to do so. There's no such thing as a free lunch.
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  #87  
Old 09-15-2018, 11:15 AM
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Originally Posted by Autoputzer View Post
Those have relatively low-pressure turbocharging, and they are tuned (de-tuned) to run on regular gas. A lot of car buyers would balk at buying a car that requires premium gas. (Similarly, a lot of car buyers would balk at buying a car that requires synthetic oil.)

Higher efficiency and higher power output is achieved by generating a hotter flame temperature, and that causes hot spots, and that causes pinging.

Even BMW de-tunes their engines to run on 91 AKI, since that's highest AKI readily available in a lot of areas. That's why all those software tuning products work. They make more torque and power, but they often need higher AKI fuel to do so. There's no such thing as a free lunch.
So for a de-tuned BMW engine tailored to 91, does ECU de-tune further when pinging is detected? The damage will be done for a very short period of time, probably for the first occurrence, or the damage/pinging happens every time engine is turned on before ECU can adjust?
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  #88  
Old 09-15-2018, 11:19 AM
heliskiier heliskiier is offline
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ECU software is designed for the US market not Europe.
Yep, exactly. We have crap gas on average in the US. Doesn't mean the car will ever be hurt and we have solid HP even on crap gas. We can buy the 93 if we want. No reason to buy it for a mellow daily commute (most of our driving) though. ECU's are a great thing. They make the most of what they have to work with.
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  #89  
Old 09-15-2018, 11:51 AM
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So for a de-tuned BMW engine tailored to 91, does ECU de-tune further when pinging is detected? The damage will be done for a very short period of time, probably for the first occurrence, or the damage/pinging happens every time engine is turned on before ECU can adjust?
It probably takes a long period of severe pinging to do physical damage to the engine. Slight, occasional pinging is just annoying. If the car's pinging that means the ECU has retarded the spark all that it can. Pinging is also can be a sign that the car is running hot. That'd be more of an immediate threat than the pinging.

I had an E46 M3. The S54 had a 11.5:1 compression ratio and was as tweaked as you can get with natural aspiration. It I was putting along in 6th, at 60 MPH, on a hot day with the AC on, it'd ping on 91 AKI if I was too lazy to downshift before accelerating. Car and Driver put an E46 M3 on a dyno and fed it various AKI's. They found that performance benefited with higher AKI up to about 96.

Have you ever see two waves on the beach collide? It shoots water way up into the air and creates a very fast moving resultant wave if they collide at any angle other than 90 degrees. A ping in a combustion chamber is similar.
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  #90  
Old 09-15-2018, 11:59 AM
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Originally Posted by Autoputzer View Post
It probably takes a long period of severe pinging to do physical damage to the engine. Slight, occasional pinging is just annoying. If the car's pinging that means the ECU has retarded the spark all that it can. Pinging is also can be a sign that the car is running hot. That'd be more of an immediate threat than the pinging.

I had an E46 M3. The S54 had a 11.5:1 compression ratio and was as tweaked as you can get with natural aspiration. It I was putting along in 6th, at 60 MPH, on a hot day with the AC on, it'd ping on 91 AKI if I was too lazy to downshift before accelerating. Car and Driver put an E46 M3 on a dyno and fed it various AKI's. They found that performance benefited with higher AKI up to about 96.

Have you ever see two waves on the beach collide? It shoots water way up into the air and creates a very fast moving resultant wave if they collide at any angle other than 90 degrees. A ping in a combustion chamber is similar.
My 335is stock liked 94/95 on a DynoJet best.
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  #91  
Old 09-15-2018, 12:35 PM
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Okay, so what grade gas do I REALLY need?

I know 2 cars in the past 15 years that had major problems because people put regular gasoline instead of premium. One was the 2nd generation Cadillac SRX with the 2.8 v6 turbo and the other was the Mazda CX-7 with the 2.5 turbo from the mazdaspeed3.
https://www.google.com/amp/s/jalopni...leaded-gas/amp


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  #92  
Old 09-15-2018, 12:40 PM
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I know 2 cars in the past 15 years that had major problem because people put regular gasoline instead of premium. One was the 2nd generation Cadillac SRX with the 3.0 v6 turbo and the other was the Mazda CX-7 with the 2.5 turbo from the mazdaspeed3.
https://www.google.com/amp/s/jalopni...leaded-gas/amp


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Super knock is definitely a thing. The computer will log it in the fault memory. Ive personally only seen it twice and the cars had a aftermarket tune.
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  #93  
Old 09-15-2018, 01:20 PM
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Elk, location not known, if you buy a top of the line car with an engine that runs like a fine watch, why would you even think about getting a lower grade gas to save a few bucks. Really!
I have neither stated nor suggested that one should do this. In fact, I have not taken a position on the question posed by the OP.

Last edited by Elk; 09-15-2018 at 01:22 PM.
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Old 09-15-2018, 02:51 PM
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I only use gas that get straight A+'s in school.
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Old 09-15-2018, 03:07 PM
Mark K Mark K is offline
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Then why are there turbo engines that run fine on 87 octane fuel?
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Originally Posted by Autoputzer View Post
Those have relatively low-pressure turbocharging, and they are tuned (de-tuned) to run on regular gas.
My experience with EA888 engine (2.0 liter turbo in my Golf GTI) so far has been:

- it does not run fine on 87 octane

- it doesn't seem like VW detuned anything to make it run "fine".

Huge caveat to this is that the coarseness and "unhappines" are mostly detected during gear changes (MT). I frankly have no problems believing that the same engine in the same car with DSG (AT) probably runs just fine as far as driver is concerned.

Just like one poster said (probably completely correctly) that some manufacturers might recommend premium so that perception is of sporty or premium car, even if engine is designed to run on regular ... I think the same thing applies in reverse. Meaning, knowing how American market perceives requirement for premium fuel (especially for low price utilitarian vehicle like Golf GTI) and knowing that software will prevent any serious damage for the duration of warranty, they simply stick "regular 87 octane recommended" sticker on the fuel door.

I normally use recommended fuel from manufacturer. Always. However, once I did fill that Golf GTI with premium for giggles, I couldn't believe the difference it made. No, not in performance, my a$$ is not that sensitive. It is simply how the engine behaves/feels like in traffic and how it reacts to throttle on/throttle off situations. Much smoother and happier sounding. Since then, I fill it up with premium. To me, it is well worth it.

My opinion simply, I do not have numbers from science lab nor do I possess Cosmic Truth.
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  #96  
Old 09-15-2018, 06:42 PM
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Nuts. I am seeking Cosmic Truth.
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Old 09-16-2018, 07:53 AM
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Nuts. I am seeking Cosmic Truth.
Me too! I think.
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Old 09-16-2018, 08:31 AM
bmwe39lover bmwe39lover is offline
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the dreaded gas and oil threads

use minimum 89 and if you want to save money and not on west coast

split 87 and 93

Do not run 87 in the n20 or n55 turbo cars the gas mileage loss negates the cost difference.. if you want to do it go to costco split premium and regular unleaded

try not to listen to all the people talking about owned 20 bmw's over years

the new cars can't run properly with regular unleaded
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  #99  
Old 04-22-2019, 12:20 PM
Wolfus Aurelius Wolfus Aurelius is offline
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Years ago I used to put premium in my Chevy every 10 tankfuls or so thinking I was giving my engine a special treat and cleaning it out until someone explained how stupid this was.


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I tried premium once in my big Buick Park Avenue, the 3.8 non-supercharged model, just to see. Mileage went down. Back to 87.

I tried it once or twice in my normally-aspirated 2.4L Buick Regal, reasoning that its compression was high enough that it might well take advantage of the 93. It did, but it didn't give enough mileage or performance increase to make up for the difference in price. Back to 87.

Since I've had the BMW 328i, I've been feeding it premium, 93. I intend to try what one of you suggested: Add just enough 87 to a full tank of 93 to have it come out as the recommended 91. That could save more than 2.00 a fill-up over, say, Exxon; more if I join Costco and start using their top-tier premium, which is vastly cheaper here than other stations. If my mileage and/or performance take a hit, I'll go back to 93.
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Old 04-22-2019, 03:18 PM
Autoputzer Autoputzer is offline
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Originally Posted by Wolfus Aurelius View Post
I tried premium once in my big Buick Park Avenue, the 3.8 non-supercharged model, just to see. Mileage went down. Back to 87.

I tried it once or twice in my normally-aspirated 2.4L Buick Regal, reasoning that its compression was high enough that it might well take advantage of the 93. It did, but it didn't give enough mileage or performance increase to make up for the difference in price. Back to 87.

Since I've had the BMW 328i, I've been feeding it premium, 93. I intend to try what one of you suggested: Add just enough 87 to a full tank of 93 to have it come out as the recommended 91. That could save more than 2.00 a fill-up over, say, Exxon; more if I join Costco and start using their top-tier premium, which is vastly cheaper here than other stations. If my mileage and/or performance take a hit, I'll go back to 93.
If you reset your OBC MPG and trip odometer when you fill up, you can accurately determine what amounts of 87 AKI and 93 AKI you'll need to achieve 91 AKI.

I'd done this on all my cars since new, and recorded all the relevant data. From this data, I've calculated the correction factor (K) (for each tank of fuel and since new) between my OBC MPG and my actual or "gas pump" MPG, where OBC MPG x (1 + K) = Gas Pump MPG. My F10 535i's K is about +1.7% since new. Frau Putzer's G01 X3 30i's K is -3.7% since new.

I divide my expected fuel purchase (miles / (OBC MPG x (1+K)) by three to determine how much 87 AKI to buy. I multiply that by two to determine how much 93 AKI I need to achieve 91 AKI. I pump the 93 AKI first, so that I get all the 93 AKI I pay for and I leave 87 AKI in the gas pump hose for the next guy.

With the OBC MPG for my current tank, the trip odometer, and "K", I can accurately estimate how much fuel I have left. If I'm using the same gas pump as I did last time, I'm usually within 0.1 gallons in my estimate.

Where I live 93 AKI is $0.60 to $0.70 more per gallon than 87 AKI. It's flat where I live. So, I don't have to worry about fuel starving on a steep hill. I can reliably run the tank down to one gallon and not worry about running out of gas. So, for a 15 gallon fill-up, I'm saving closer to $3/tank. That's enough for one of those tasty corn dogs inside the store, or even some Hostess Ding Dong's.

I wrote Frau Putzer instructions for filling up her X3 with 91 AKI and collecting the necessary data. I then printed the instructions on heavy stock paper and had them laminated. It's in the pouch on the back of the driver's seat along with three "DO DONT WASH" signs (also laminated and printed on heavy stock paper). When her car/truck gets low on gas, she says:

"My X3 is low on gas. If I fill it up I'm going to use all 87 AKI or all 93 AKI, and I'm gong to **** up collecting all the data. Do you want to fill it up, instead.... ***hole?"

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Last edited by Autoputzer; 04-22-2019 at 05:12 PM.
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