# Shell Regular $1.41, +30¢ Midgrade $1.71, +20¢ Premium $1.91 Why such difference? **URL:** \ **Category:** General Discussion\ **Created:** [February 15, 2016, 8:57pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531 "2016-02-15T20:57:06Z")\ **Posts on this page:** 14\ **Page:** 3
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 18, 2016, 2:39am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/41 "2016-02-18T02:39:26Z")
2008 Ford Expedition manual: > _**Your vehicle is designed to use "Regular" unleaded with pump (R+M)/2 octane rating of 87. We do not recommend the use of gasolines labeled as "Regular" that are sold with octane ratings of 86 or lower in high altitude areas.**_ Costco’s two fuels are 85 and 91 octane. Have never heard any pinging, but I also accelerate gently. On emergentransports I have done full throttle on mountain upgrades to just maintain the speed limit, but at 65 to 75 mph wind noise can cover pinging. ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [February 18, 2016, 3:15am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/42 "2016-02-18T03:15:46Z")
> **Costco's two fuels are 85 and 91 octane. Have never heard any pinging, but I also accelerate gently.** The reason you may not be hearing any pinging is because the anti-knock sensor is working and detecting pinging then backs off the timing. Gas mileage and acceleration can be adversely effected. ---
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 18, 2016, 7:43am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/43 "2016-02-18T07:43:54Z")
^ Love to know how it detects knocking. ---
**Author:** ![SteveCBT](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevecbt/32/3192_2.png) [@SteveCBT](https://community.cartalk.com/u/SteveCBT)\ **Post date:** [February 18, 2016, 8:44am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/44 "2016-02-18T08:44:46Z")
Google is your friend [https://www.picoauto.com/library/automotive-guided-tests/knock-sensor](https://www.picoauto.com/library/automotive-guided-tests/knock-sensor) ---
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 18, 2016, 1:22pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/45 "2016-02-18T13:22:20Z")
Thank you. Video fails to explain what it detects. _"The frequency of the vibration caused by knocking (pinking) is about 15 kHz."_ Now that is good! Thank you. ---
**Author:** ![kmccune](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/kmccune/32/1237_2.png) [@kmccune](https://community.cartalk.com/u/kmccune)\ **Post date:** [February 18, 2016, 5:28pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/46 "2016-02-18T17:28:28Z")
Think there was a puzzler once about a mysterious car or engine problem ,had something to do with performance ,anyway it was traced back finally to something or the other that was loose ,when it "knocked " it activated the knock sensor and changed the engine performance . ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [February 18, 2016, 7:21pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/47 "2016-02-18T19:21:07Z")
It’s a microphone. It could theoretically be used to detect other problems like rod knock vs piston slap etc. Anyone here ever look at its output on a scope? ---
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 18, 2016, 9:00pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/48 "2016-02-18T21:00:27Z")
^ Yes. If one can identify the waveforms of various problems or potential problems and a transducer can detect the waveforms, the computer can recognize and notify. Lucky that (an engine’s) pinging is within a narrow-enough frequency range that it can be readily identified. Is the pinging a lower frequency the larger the cylinder? ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 20, 2016, 4:39am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/49 "2016-02-20T04:39:23Z")
Today, at Costco, I noted the following gas prices, per gallon: Regular–$1.41 Premium–$1.82 That’s enough of a price differential for me to be very glad that my engine requires only the cheap stuff. ---
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 20, 2016, 6:17am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/50 "2016-02-20T06:17:39Z")
Our Costco $1.33/ gal. 85 octane = 1.56¢/octane point $1.69/ gal. 91 octane = 1.85¢/octane point 50/50 Regular/Premium = $1.51/gal. 88 octane = 1.71¢/octane point ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [February 20, 2016, 4:46pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/51 "2016-02-20T16:46:45Z")
Another method of detecting detonation is by measuring the voltage needed to ionize the air in the spark plug spark gap. The higher the cylinder pressure, the higher the voltage has to be to jump a spark, in case you ever wondered why engines with weak ignition systems or worn spark plugs misfire at full throttle but work fine at part throttle. After the main spark, a string of follow up sparks happens not only to insure ignition but also the voltage needed to ionize the air indicates the pressure rise in the cylinder. A sudden precipitous rise in pressure indicates detonation. Misfires can also be detected by the absence of a pressure rise after the main spark. I believe Harley Davidson used this system on some of its models. If you put the wrong spark plugs or plug wires on these models, you would get a “check engine” light. ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [February 20, 2016, 4:58pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/52 "2016-02-20T16:58:37Z")
I must be way behind the times, I didn’t know Harley’s even have a CEL. I guess I need to learn to keep up. ---
**Author:** ![Robert-Gift](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/robert-gift/32/356_2.png) [@Robert-Gift](https://community.cartalk.com/u/Robert-Gift)\ **Post date:** [February 20, 2016, 5:04pm UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/53 "2016-02-20T17:04:46Z")
What an elegant way of detection! (My Kawasaki’s Check Engine Light was a 100-Watt rough service bulb on an extension cord.) ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [February 21, 2016, 3:40am UTC](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531/54 "2016-02-21T03:40:39Z")
> I must be way behind the times, I didn't know Harley's even have a CEL. I guess I need to learn to keep up. Harleys have to be EPA compliant just like Hondas. Even though HD has been stereotyped as resisting new technology at all costs, in reality, they were one of the earliest adapters of EFI in motorcycles, offering mostly EFI bikes back when Honda, Yamaha, Kawasaki, and Suzuki’s all mostly still had carbs. They weren’t the very first, but they were leaders in offering EFI in the majority of their lineup. [Previous page](https://community.cartalk.com/t/shell-regular-1-41-30-midgrade-1-71-20-premium-1-91-why-such-difference/92531.md?page=2)