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
