Re: [MBZ] O.T. Octane and Knock Sensors
Agreed, higher octane also resists ignition due to compression. If the reason for pinging was high compression there isn't much the computer can do about it. I suppose that in a forced induction engine it could open the waste gate to reduce boost or if it was a VNT turbo just make less boost in the first place. I dislike these kind of articles, they true but only to a point. You get some chowder head driving a high compression engine hard and they'll burn it down with cheap gas... Curt Sent from Yahoo Mail on Android On Sat, Sep 30, 2023 at 9:56 AM, MG via Mercedes wrote: > Accurate or BS? Well yes and no. Here is some of what I learned by reading the Bosch Automotive Technology handbook. > What is the difference between higher octane and lower octane? > Well, 87 octane will ignite at a lower pressure than 93 octane. Here he is wrong. We all know from our experiments in igniting items that require burning, that gasoline will ignite in open air without pressure no matter what octane it is. So the real explanation is that both low and high octane will ignite at the same pressure but lower octane gas will burn faster at a given pressure than higher octane. This isn't normally noticed by our slow senses but in the cylinder the flame front rate of the burning will travel faster in low octane fuel than in a higher octane. The higher the octane, the slower the burn rate. If the pressure in the cylinder is increased the molecules are squeezed together more thus increasing the burn rate in any octane fuel, till what results is a rather quick and sudden explosion. Again at a lower pressure for lower octane vs. higher octane. This results in all the way from a slight ping of the valves being shoved closed faster than the spring rate on the valve springs were designed for, to a sudden louder more violent knock of a piston slap and or rod knock in more severe cases, from overpressure rather than a controlled progressive burn as the engineers intended. This has even been known to break crankshafts or totally destroy engines as is seen in drag racing all the time. Increasing the octane reduces that burn rate giving time for the piston to get over TDC. So in the end a slightly earlier ignition timing or higher compression or both can be used to get more power from the same amount of gas or more gas and air can be inducted and thus allowing even more power to be produced. > So, with 93 octane, you can compress the air (think turbo or supercharger) > and have the > spark ignite sooner (timing advance) which creates more power. With 87 octane, since it change here to explodes or detonates not just > ignites at a lower pressure, > high compression engines might ignite the gas before the intake valve closes and you > hear a noise (ping). Often, in old cars, you will hear this pinging under load (moderate > throttle going uphill). What this noise is, is the detonation of the gas and air mixture or exploding > in your cylinders before the intake valve is closed. The explosion is > partially sent into the intake not..., some of the gas and air mixture might get pushed back but no actual explosion or flame because in that case you would get an immediate backfire and flame out of the carburetor. Or in the case of drag racing seeing your supercharger get blown off the engine. > causing the noise. What a knock sensor does is detect this noise (the “pings” > or “knocks”) > and tells the computer to spark/ignite at a slightly later time. > Which allows the piston to travel over TDC and reduce the pressure and speed of the burn. Though usually the detected ping is so small before it is corrected that most people don't even notice it. > *The only reason the manufacture tells you that you have to run premium fuel > if that the > vehicle was tested for gas mileage with premium. Running premium will get you > slightly > more power per molecule of fuel, thus better gas mileage. If you run 87 octane, you might > get slightly (and I mean slightly) Probably 1-2 MPG which can always be excused by citing driving technique > less gas mileage out of your vehicle. The manufacture > doesn’t want to get sued for advertising a certain MPG and you getting slightly less. They > have to tell you to run premium or risk litigation with the EPS or the consumer.” > > Accurate or BS? > > AZBob > > Sent from my iPhone > ___ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > > > ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com ___
Re: [MBZ] O.T. Octane and Knock Sensors
> Accurate or BS? Well yes and no. Here is some of what I learned by reading the Bosch Automotive Technology handbook. > What is the difference between higher octane and lower octane? > Well, 87 octane will ignite at a lower pressure than 93 octane. Here he is wrong. We all know from our experiments in igniting items that require burning, that gasoline will ignite in open air without pressure no matter what octane it is. So the real explanation is that both low and high octane will ignite at the same pressure but lower octane gas will burn faster at a given pressure than higher octane. This isn't normally noticed by our slow senses but in the cylinder the flame front rate of the burning will travel faster in low octane fuel than in a higher octane. The higher the octane, the slower the burn rate. If the pressure in the cylinder is increased the molecules are squeezed together more thus increasing the burn rate in any octane fuel, till what results is a rather quick and sudden explosion. Again at a lower pressure for lower octane vs. higher octane. This results in all the way from a slight ping of the valves being shoved closed faster than the spring rate on the valve springs were designed for, to a sudden louder more violent knock of a piston slap and or rod knock in more severe cases, from overpressure rather than a controlled progressive burn as the engineers intended. This has even been known to break crankshafts or totally destroy engines as is seen in drag racing all the time. Increasing the octane reduces that burn rate giving time for the piston to get over TDC. So in the end a slightly earlier ignition timing or higher compression or both can be used to get more power from the same amount of gas or more gas and air can be inducted and thus allowing even more power to be produced. So, with 93 octane, you can compress the air (think turbo or supercharger) and have the > spark ignite sooner (timing advance) which creates more power. With 87 octane, since it change here to explodes or detonates not just ignites at a lower pressure, > high compression engines might ignite the gas before the intake valve closes and you > hear a noise (ping). Often, in old cars, you will hear this pinging under load (moderate > throttle going uphill). What this noise is, is the detonation of the gas and air mixture or exploding in your cylinders before the intake valve is closed. The explosion is partially sent into the intake not..., some of the gas and air mixture might get pushed back but no actual explosion or flame because in that case you would get an immediate backfire and flame out of the carburetor. Or in the case of drag racing seeing your supercharger get blown off the engine. causing the noise. What a knock sensor does is detect this noise (the “pings” or “knocks”) and tells the computer to spark/ignite at a slightly later time. Which allows the piston to travel over TDC and reduce the pressure and speed of the burn. Though usually the detected ping is so small before it is corrected that most people don't even notice it. *The only reason the manufacture tells you that you have to run premium fuel if that the vehicle was tested for gas mileage with premium. Running premium will get you slightly > more power per molecule of fuel, thus better gas mileage. If you run 87 octane, you might > get slightly (and I mean slightly) Probably 1-2 MPG which can always be excused by citing driving technique less gas mileage out of your vehicle. The manufacture > doesn’t want to get sued for advertising a certain MPG and you getting slightly less. They > have to tell you to run premium or risk litigation with the EPS or the consumer.” Accurate or BS? AZBob Sent from my iPhone ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] O.T. Octane and Knock Sensors
I would base it on the compression ratio of the engine. Yes knock sensor will retard the spark but at some point if it's a high compression engine you will get detonation with lower octane fuel. Why not run 85 or 82 if it's such a good idea? On Fri, Sep 29, 2023, at 17:26, Bob Rentfro via Mercedes wrote: > A car guy friend posted this about knock sensors and octane #s. Will > this make us all run out and burn 87 in our 91 only cars? > > “Short story on knock sensors: All modern cars have them. And because > of knock sensors, you can run 87 octane in a vehicle that says you have > to run premium*. > > Long story on knock sensors: Let’s start with gasoline. It typically > comes in 87, 89, 91, 92, 93 octane at the pump. Drag strips etc. often > have even higher octane. What is the difference between higher octane > and lower octane? Well, 87 octane will ignite at a lower pressure than > 93 octane. So, with 93 octane, you can compress the air (think turbo or > supercharger) and have the spark ignite sooner (timing advance) which > creates more power. With 87 octane, since it ignites at a lower > pressure, high compression engines might ignite the gas before the > intake valve closes and you hear a noise (ping). Often, in old cars, > you will hear this pinging under load (moderate throttle going uphill). > What this noise is, is the detonation of the gas and air mixture in > your cylinders igniting before the intake valve is closed. The > explosion is partially sent into the intake causing the noise. What a > knock sensor does is detect this noise (the “pings” or “knocks”) and > tells the computer to spark/ignite at a slightly later time. > > *The only reason the manufacture tells you that you have to run premium > fuel if that the vehicle was tested for gas mileage with premium. > Running premium will get you slightly more power per molecule of fuel, > thus better gas mileage. If you run 87 octane, you might get slightly > (and I mean slightly) less gas mileage out of your vehicle. The > manufacture doesn’t want to get sued for advertising a certain MPG and > you getting slightly less. They have to tell you to run premium or risk > litigation with the EPS or the consumer.” > > Accurate or BS? > > AZBob > > Sent from my iPhone > ___ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] O.T. Octane and Knock Sensors
I run 87 in my m112 and I can’t tell any difference in power or mileage Sent from my iPhone > On Sep 29, 2023, at 5:27 PM, Bob Rentfro via Mercedes > wrote: > > A car guy friend posted this about knock sensors and octane #s. Will this > make us all run out and burn 87 in our 91 only cars? > > “Short story on knock sensors: All modern cars have them. And because of > knock sensors, you can run 87 octane in a vehicle that says you have to run > premium*. > > Long story on knock sensors: Let’s start with gasoline. It typically comes in > 87, 89, 91, 92, 93 octane at the pump. Drag strips etc. often have even > higher octane. What is the difference between higher octane and lower octane? > Well, 87 octane will ignite at a lower pressure than 93 octane. So, with 93 > octane, you can compress the air (think turbo or supercharger) and have the > spark ignite sooner (timing advance) which creates more power. With 87 > octane, since it ignites at a lower pressure, high compression engines might > ignite the gas before the intake valve closes and you hear a noise (ping). > Often, in old cars, you will hear this pinging under load (moderate throttle > going uphill). What this noise is, is the detonation of the gas and air > mixture in your cylinders igniting before the intake valve is closed. The > explosion is partially sent into the intake causing the noise. What a knock > sensor does is detect this noise (the “pings” or “knocks”) and tells the > computer to spark/ignite at a slightly later time. > > *The only reason the manufacture tells you that you have to run premium fuel > if that the vehicle was tested for gas mileage with premium. Running premium > will get you slightly more power per molecule of fuel, thus better gas > mileage. If you run 87 octane, you might get slightly (and I mean slightly) > less gas mileage out of your vehicle. The manufacture doesn’t want to get > sued for advertising a certain MPG and you getting slightly less. They have > to tell you to run premium or risk litigation with the EPS or the consumer.” > > Accurate or BS? > > AZBob > > Sent from my iPhone > ___ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
[MBZ] O.T. Octane and Knock Sensors
A car guy friend posted this about knock sensors and octane #s. Will this make us all run out and burn 87 in our 91 only cars? “Short story on knock sensors: All modern cars have them. And because of knock sensors, you can run 87 octane in a vehicle that says you have to run premium*. Long story on knock sensors: Let’s start with gasoline. It typically comes in 87, 89, 91, 92, 93 octane at the pump. Drag strips etc. often have even higher octane. What is the difference between higher octane and lower octane? Well, 87 octane will ignite at a lower pressure than 93 octane. So, with 93 octane, you can compress the air (think turbo or supercharger) and have the spark ignite sooner (timing advance) which creates more power. With 87 octane, since it ignites at a lower pressure, high compression engines might ignite the gas before the intake valve closes and you hear a noise (ping). Often, in old cars, you will hear this pinging under load (moderate throttle going uphill). What this noise is, is the detonation of the gas and air mixture in your cylinders igniting before the intake valve is closed. The explosion is partially sent into the intake causing the noise. What a knock sensor does is detect this noise (the “pings” or “knocks”) and tells the computer to spark/ignite at a slightly later time. *The only reason the manufacture tells you that you have to run premium fuel if that the vehicle was tested for gas mileage with premium. Running premium will get you slightly more power per molecule of fuel, thus better gas mileage. If you run 87 octane, you might get slightly (and I mean slightly) less gas mileage out of your vehicle. The manufacture doesn’t want to get sued for advertising a certain MPG and you getting slightly less. They have to tell you to run premium or risk litigation with the EPS or the consumer.” Accurate or BS? AZBob Sent from my iPhone ___ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
