Mid-grade gas math (Page 1 of 2)
Posted: 4/28/2026 9:05:36 PM EDT
[Last Edit: MJ11B4P][Edited]
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I ended up getting a new Tacoma, and it doesn’t seem to like regular 87… occasional light knock and possibly less than ideal fuel economy (inconclusive on the economy). This is a new one for me, as I’ve never had a vehicle designed for regular pump gas need a higher octane fuel. Fuel prices at my usual Texaco are: 87 @ $3.689 89 @ $4.189 93 @ $4.589 If mid-grade is 87 and 93 blended at the pump, then 89 is a 2:1 mix… 67% 87 + 33% 93. The fair price for 89 should be $3.989… if it were 1:1 mix for 90 octane, it should be $4.139. Outside of pricing fuckery, is this standard practice or just my local stations? Or is my math off? |
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Originally Posted By MJ11B4P: I ended up getting a new Tacoma, and it doesn’t seem to like regular 87… occasional light knock and possibly less than ideal fuel economy (inconclusive on the economy). This is a new one for me, as I’ve never had a vehicle designed for regular pump gas need a higher octane fuel. Fuel prices at my usual Texaco are: 87 @ $3.689 89 @ $4.189 93 @ $4.589 If mid-grade is 87 and 93 blended at the pump, then 89 is a 2:1 mix… 67% 87 + 33% 93. The fair price for 89 should be $3.989… if it were 1:1 mix for 90 octane, it should be $4.139. Outside of pricing fuckery, is this standard practice or just my local stations? Or is my math off? What's is say on the gas tank lid? What octane SHOULD you be running in it? If it's knocking with 87, and the DME can't pull enough timing out of it to get it to stop...I'm guessing it's supposed to be running 91? You spent a fortune on a new vehicle.....spend a few extra dollars when you fill it up and put the correct octane of fuel in it.....  Good lord....
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Originally Posted By ALASKANFIRE: They get to make their own rules. If my car was designed to run on 87 and was knocking I'd be contacting Toyota and find out why. This. Modern cars will keep pulling timing to keep a cylinder from knocking/detonating....even if you are running supper low octane fuel. If it is actually knocking on you...I would have someone see what's going on. I can't remember the last time I'm ever heard a newer fuel injected motor actually knock. And if it actually does (because the DME can't pull enough timing out of it)...it will throw a check engine like/code for "superknock" or something similar. |
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Thank you for sharing some great wisdom here. Glad I didn’t post this in GD. -Yes, the owner’s manual calls out 87 or higher. -$39k is not a ridiculous amount or “fortune” for a new truck -the T24A engine make a lot of odd noises… sounds like light knocking under certain conditions; might not be. Seemed to like a higher octane fuel. I was more concerned about mid-grade gas pricing… I’ll continue to check stations to see if there’s a premium on mid-grade. Thanks! |
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Originally Posted By MJ11B4P: Thank you for sharing some great wisdom here. Glad I didn’t post this in GD. -Yes, the owner’s manual calls out 87 or higher. -$39k is not a ridiculous amount or “fortune” for a new truck -the T24A engine make a lot of odd noises… sounds like light knocking under certain conditions; might not be. Seemed to like a higher octane fuel. I was more concerned about mid-grade gas pricing… I’ll continue to check stations to see if there’s a premium on mid-grade. Thanks! So that vehicle is good. You’re just “concerned” about mid grade fuel pricing? What exactly do you intend to do about it? |
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Originally Posted By ColtRifle: So that vehicle is good. You’re just “concerned” about mid grade fuel pricing? What exactly do you intend to do about it? Originally Posted By ColtRifle: Originally Posted By MJ11B4P: Thank you for sharing some great wisdom here. Glad I didn’t post this in GD. -Yes, the owner’s manual calls out 87 or higher. -$39k is not a ridiculous amount or “fortune” for a new truck -the T24A engine make a lot of odd noises… sounds like light knocking under certain conditions; might not be. Seemed to like a higher octane fuel. I was more concerned about mid-grade gas pricing… I’ll continue to check stations to see if there’s a premium on mid-grade. Thanks! So that vehicle is good. You’re just “concerned” about mid grade fuel pricing? What exactly do you intend to do about it? One quite obvious thing is he's going to ask here if anyone knows the logic of the pricing. It's something I'd never thought about, and he laid out quite the interesting scenario. It's likely someone here knows how that works. |
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Originally Posted By Bohr_Adam: One quite obvious thing is he's going to ask here if anyone knows the logic of the pricing. It's something I'd never thought about, and he laid out quite the interesting scenario. It's likely someone here knows how that works. This guy gets it. Just curious if pricing fuckery for mid-grade is widespread or localized. Probably should have posted in Foxtrot08’s oil thread |
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Originally Posted By Bohr_Adam: One quite obvious thing is he's going to ask here if anyone knows the logic of the pricing. It's something I'd never thought about, and he laid out quite the interesting scenario. It's likely someone here knows how that works. They know if you need mid or top level gas you will pay the extra even if it is inflated. $39K for a mini truck with a 4 cyl is a fortune. |
Guy comes here to ask about the economics of blended gasoline. Gets lambasted for spending reasonable, middle of the road money for a truck. A "fortune" on a truck should start at six figures, which many of the ones on the road are now. This place has gotten so fucked up. 
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| Quite a few years ago I commuted from Seattle to Everett to work at a client's shop. That's a pretty long haul for a daily commute in my Tacoma, so I started paying attention to fuel cost. Over the course of a summer I tried every fuel grade including ethanol-free, and calculated cost per mile. Turned out the cost per mile was exactly the same for all grades. And etoh-free's higher mpg meant I didn't have to stop and tank up every Thursday. I still run etoh-free. |
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Originally Posted By MJ11B4P: I ended up getting a new Tacoma, and it doesn't seem to like regular 87 occasional light knock and possibly less than ideal fuel economy (inconclusive on the economy). This is a new one for me, as I've never had a vehicle designed for regular pump gas need a higher octane fuel. Fuel prices at my usual Texaco are: 87 @ $3.689 89 @ $4.189 93 @ $4.589 If mid-grade is 87 and 93 blended at the pump, then 89 is a 2:1 mix 67% 87 + 33% 93. The fair price for 89 should be $3.989 if it were 1:1 mix for 90 octane, it should be $4.139. Outside of pricing fuckery, is this standard practice or just my local stations? Or is my math off? |
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Gas companies set fuel prices by what generates the most profit, not simply adding a fixed profit on top of their cost. Many of the newer Toyota engines have so much timing that the ecu will routinely be retarding timing due to the knock. You can often hear the light pinging too. I swapped an AR engine (2010s era, predecessor to the T engine) into an old car and the knock was immediately apparent. The original manual said to use 87 and using higher grade didn't change anything. Did the swap over 2 years ago and have 20k miles on it, no issues so far. Get an OBD scanner and there will be parameters you can watch for knock and the resulting timing retard if you want to confirm whether what you are hearing is knock. |
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Originally Posted By TNC: Quite a few years ago I commuted from Seattle to Everett to work at a client's shop. That's a pretty long haul for a daily commute in my Tacoma, so I started paying attention to fuel cost. Over the course of a summer I tried every fuel grade including ethanol-free, and calculated cost per mile. Turned out the cost per mile was exactly the same for all grades. And etoh-free's higher mpg meant I didn't have to stop and tank up every Thursday. I still run etoh-free. Ethanol is just government subsidizing corn producers. It theoretically offers something more than nothing, but I've had the same experience taking note of my mileage on road trips. 10% ethanol is roughly a 10% reduction in fuel economy. Not a fan. Octane is totally different, and I see zero value in using a higher octane rating than needed. |
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Originally Posted By PoopdeckPappy: It is standard practice. It even has a name. The mid-grade premium or sometimes the 89 tax. A lot of places price it right between regular and premium, because to a layman's logic it's the middle grade, so pricing it in the middle would make simple sense. If you want to beat the gas stations at their little "scheme", just do two transactions of 2-parts regular and 1-part premium and let them splash blend in your tank. |
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Originally Posted By Bohr_Adam: Ethanol is just government subsidizing corn producers. It theoretically offers something more than nothing, but I've had the same experience taking note of my mileage on road trips. 10% ethanol is roughly a 10% reduction in fuel economy. Not a fan. Octane is totally different, and I see zero value in using a higher octane rating than needed. Depends entirely on the car. Some vehicles spec 87 as minimum, but will make significantly more power on 93. OP, as others have posted, if your new Taco is pinging, something isn't right. Audible knock is the equivalent of banging your pistons with a hammer. Go to the dealer. WRT to your comment on fuel economy - It's a Taco. They and the Tundra have always had among the worst if not worst in class fuel economy. |
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I always figured (maybe incorrectly) that a 50/50 mix would be 90-91 octane, and if the midgrade was really 89 it might be less than half premium. So when trying to save money in my premium fueled vehicle, I used to put 5-10 gallons of premium in, and then finish filling with regular. That also had the advantage of not leaving a hoseful of premium or midgrade that I paid for behind at the pump. And I could adjust the mix for weather. If it was cold, it seemed to run fine on 5 gallons of premium and 15 gallons of regular. Go ahead and flame me. |
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Originally Posted By MJ11B4P: Thank you for sharing some great wisdom here. Glad I didn’t post this in GD. -Yes, the owner’s manual calls out 87 or higher. -$39k is not a ridiculous amount or “fortune” for a new truck -the T24A engine make a lot of odd noises… sounds like light knocking under certain conditions; might not be. Seemed to like a higher octane fuel. I was more concerned about mid-grade gas pricing… I’ll continue to check stations to see if there’s a premium on mid-grade. Thanks! If it's knocking you would get a CEL. You are probably hearing the fuel injectors. The Taco uses direct and port injection. it mixes it up for optimum mpg, exhaust gas and preventing carbon build up on valves. If it's a new truck, your MPG isn't going to be anything near whats posted on the window sticker. My 2017 tacamoa 4x4 was lucky to get 19mpg mixed. |
| My 2015 Taco LOVES non ethanol gas [89] over regular or mid grade. Since I don't drive it much, I prefer non ethanol gas over 90/10. Miata prefers non ethanol or premium, 87 WILL spark knock under load/low RPM. Honda doesn't give a damn either way. |
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Thanks to those that chimed in. Honestly, I can’t recall ever buying mid-grade gas. I had an Acura about 20 years ago that called for premium - and it ran better with premium - but not enough to offset the cost over regular. This new Taco and its T24A engine is…different. In a mostly good way. I’m familiar with D4S and weird noises, this one puts injector noise front and center like it’s a selling point. Never been a fan of forced induction for longevity, but whatever, time marches on. The “knock” may or not be. It’s certainly not worth engaging the dealer at this point. If the engine grenades, then that’s a different story. I’ll continue to monitor. My scanner doesn’t log detonations/knock events, so might look into a new one. This is the first Toyota I’ve owned that has been off from advertised MPG. I’m sure it’s most likely from the right foot interface than anything. Anyway, back to the “89 Tax” yeh that’s a new one for me. Appreciate the heads up. |
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Originally Posted By MJ11B4P: Thanks to those that chimed in. Honestly, I can’t recall ever buying mid-grade gas. I had an Acura about 20 years ago that called for premium - and it ran better with premium - but not enough to offset the cost over regular. This new Taco and its T24A engine is…different. In a mostly good way. I’m familiar with D4S and weird noises, this one puts injector noise front and center like it’s a selling point. Never been a fan of forced induction for longevity, but whatever, time marches on. The “knock” may or not be. It’s certainly not worth engaging the dealer at this point. If the engine grenades, then that’s a different story. I’ll continue to monitor. My scanner doesn’t log detonations/knock events, so might look into a new one. This is the first Toyota I’ve owned that has been off from advertised MPG. I’m sure it’s most likely from the right foot interface than anything. Anyway, back to the “89 Tax” yeh that’s a new one for me. Appreciate the heads up. Modern vehicles will dial back timing, sometimes a lot if spark knock occurs so you can quite often feel the difference IF the manufacturer of your vehicle calls for premium gas to be used in the model you bought. |
Liberals are a curious mix of communism and fascism, they want to destroy you but want to use your own money to do it.
I'm getting down to the last box, the others have all been destroyed...
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Originally Posted By MJ11B4P: Does he do retail fuels? I thought he was strictly a wholesale distributor for lubricants. Originally Posted By MJ11B4P: Originally Posted By 545days: This is a good thread for @foxtrot08 to chime in on. Does he do retail fuels? I thought he was strictly a wholesale distributor for lubricants. I personally am on the wholesale fuels and lubricants. My family owns one of the largest C store chains in the U.S. The best way I can phrase retail gasoline prices is, don’t think too hard about it. Mid grade is blended at the pump. The price at the pump has very little to do with the actual cost. But more to do with what the market will bear. So the gap between regular / mid grade / premium. Historically was 10 cents. Then moved to 20. Now it’s like 40 cents and then like $1.20. It’s completely whacky because they can make it. |
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Originally Posted By Foxtrot08: I personally am on the wholesale field and lubricants. My family owns one of the largest C store chains in the U.S. The best way I can phrase retail gasoline prices is, don’t think too hard about it. Mid grade is blended at the pump. The price at the pump has very little to do with the actual cost. But more to do with what the market will bear. So the gap between regular / mid grade / premium. Historically was 10 cents. Then moved to 20. Now it’s like 40 cents and then like $1.20. It’s completely whacky because they can make it. Originally Posted By Foxtrot08: Originally Posted By MJ11B4P: Originally Posted By 545days: This is a good thread for @foxtrot08 to chime in on. Does he do retail fuels? I thought he was strictly a wholesale distributor for lubricants. I personally am on the wholesale field and lubricants. My family owns one of the largest C store chains in the U.S. The best way I can phrase retail gasoline prices is, don’t think too hard about it. Mid grade is blended at the pump. The price at the pump has very little to do with the actual cost. But more to do with what the market will bear. So the gap between regular / mid grade / premium. Historically was 10 cents. Then moved to 20. Now it’s like 40 cents and then like $1.20. It’s completely whacky because they can make it. I appreciate that succinct explanation. That is consistent with what I am seeing. If I’m in need more octane, I’ll be dosing with premium. |
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Originally Posted By MJ11B4P: I appreciate that succinct explanation. That is consistent with what I am seeing. If I’m in need more octane, I’ll be dosing with premium. Originally Posted By MJ11B4P: Originally Posted By Foxtrot08: Originally Posted By MJ11B4P: Originally Posted By 545days: This is a good thread for @foxtrot08 to chime in on. Does he do retail fuels? I thought he was strictly a wholesale distributor for lubricants. I personally am on the wholesale field and lubricants. My family owns one of the largest C store chains in the U.S. The best way I can phrase retail gasoline prices is, don’t think too hard about it. Mid grade is blended at the pump. The price at the pump has very little to do with the actual cost. But more to do with what the market will bear. So the gap between regular / mid grade / premium. Historically was 10 cents. Then moved to 20. Now it’s like 40 cents and then like $1.20. It’s completely whacky because they can make it. I appreciate that succinct explanation. That is consistent with what I am seeing. If I’m in need more octane, I’ll be dosing with premium. When I’m on long road trips. I mix my own 91 octane. My raptor I tune my raptor for 91 octane when I do road trips. (Cobb tuned) So I mix regular and premium. Instead of buying mid grade. Just because I chuckle at the price. And it’s one more card swipe, why not. |
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Originally Posted By Morgan321: Gas companies set fuel prices by what generates the most profit, not simply adding a fixed profit on top of their cost. Many of the newer Toyota engines have so much timing that the ecu will routinely be retarding timing due to the knock. You can often hear the light pinging too. I swapped an AR engine (2010s era, predecessor to the T engine) into an old car and the knock was immediately apparent. The original manual said to use 87 and using higher grade didn't change anything. Did the swap over 2 years ago and have 20k miles on it, no issues so far. Get an OBD scanner and there will be parameters you can watch for knock and the resulting timing retard if you want to confirm whether what you are hearing is knock. People are finding the BRZ/GR86 are pulling timing with 93 Octane. I havent checked mine with mine, but it wouldnt surprise me. I've never heard any detonation though. I'd be inquiring about having it checked under warranty if I did. The direct/port fuel injection system can be loud and made concerning noises, louder exhaust fixed that issue. You may be hearing the fueling system. Look at deleting the charcoal filter from the airbox too. Crazy they put that shit in there. |
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I didn’t want to get too deep into the knocking topic because I thought it was pretty a fairly common issue with TGDI engines… I’m not talking about LSPI events, just mild abnormal combustion under certain operating conditions… in my case, it seems to occur under moderate loads with moderate throttle. It’s very subtle and I’m not terribly concerned about it for now. Otherwise, the truck would be at the dealership. Sometimes simply running a better quality fuel is the easy answer. I wonder sometimes if we’re at the point in engine development that fuel quality is a limiting factor… seems like this was an issue 20-25 years ago with oil. |
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ETA: now that I think about it it could be a transition point between port and direct injection or mixed regime 🤔 something I’ve never felt in a 2GR or natural aspirated D4S engine. Regardless, it’s a bit more complex than just the ECU pulling timing. |
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Originally Posted By dangerranger61007: People are finding the BRZ/GR86 are pulling timing with 93 Octane. I havent checked mine with mine, but it wouldnt surprise me. I've never heard any detonation though. I'd be inquiring about having it checked under warranty if I did. The direct/port fuel injection system can be loud and made concerning noises, louder exhaust fixed that issue. You may be hearing the fueling system. Look at deleting the charcoal filter from the airbox too. Crazy they put that shit in there. Originally Posted By dangerranger61007: Originally Posted By Morgan321: Gas companies set fuel prices by what generates the most profit, not simply adding a fixed profit on top of their cost. Many of the newer Toyota engines have so much timing that the ecu will routinely be retarding timing due to the knock. You can often hear the light pinging too. I swapped an AR engine (2010s era, predecessor to the T engine) into an old car and the knock was immediately apparent. The original manual said to use 87 and using higher grade didn't change anything. Did the swap over 2 years ago and have 20k miles on it, no issues so far. Get an OBD scanner and there will be parameters you can watch for knock and the resulting timing retard if you want to confirm whether what you are hearing is knock. People are finding the BRZ/GR86 are pulling timing with 93 Octane. I havent checked mine with mine, but it wouldnt surprise me. I've never heard any detonation though. I'd be inquiring about having it checked under warranty if I did. The direct/port fuel injection system can be loud and made concerning noises, louder exhaust fixed that issue. You may be hearing the fueling system. Look at deleting the charcoal filter from the airbox too. Crazy they put that shit in there. My direct port injection BMW gas motor sounds like a diesel....those injectors tick pretty loud when they have 2,000psi of fuel running through them. |
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Originally Posted By imq707s: My direct port injection BMW gas motor sounds like a diesel....those injectors tick pretty loud when they have 2,000psi of fuel running through them. Originally Posted By imq707s: Originally Posted By dangerranger61007: Originally Posted By Morgan321: Gas companies set fuel prices by what generates the most profit, not simply adding a fixed profit on top of their cost. Many of the newer Toyota engines have so much timing that the ecu will routinely be retarding timing due to the knock. You can often hear the light pinging too. I swapped an AR engine (2010s era, predecessor to the T engine) into an old car and the knock was immediately apparent. The original manual said to use 87 and using higher grade didn't change anything. Did the swap over 2 years ago and have 20k miles on it, no issues so far. Get an OBD scanner and there will be parameters you can watch for knock and the resulting timing retard if you want to confirm whether what you are hearing is knock. People are finding the BRZ/GR86 are pulling timing with 93 Octane. I havent checked mine with mine, but it wouldnt surprise me. I've never heard any detonation though. I'd be inquiring about having it checked under warranty if I did. The direct/port fuel injection system can be loud and made concerning noises, louder exhaust fixed that issue. You may be hearing the fueling system. Look at deleting the charcoal filter from the airbox too. Crazy they put that shit in there. My direct port injection BMW gas motor sounds like a diesel....those injectors tick pretty loud when they have 2,000psi of fuel running through them. I can definitively pinpoint injector noises; this is not it. Diesel rattle is a decent analogy, but very subtle… not the 2GR cleaning cycle. This while actively driving. |
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39k is not a fortune, esp for a truck that may not depreciate more than 25 percent over 5 years. We've all seen some crazy retention with Toyotas, God knows why. My Hyundai runs a 2.5 liter turbo 4 making 290 HP- very similar numbers to the 2.4l @ 285HP of the Tacoma and it sewing machine quiet at most speeds and with 87 octane, even when I hit it. I'm not sure why your truck is making odd noises, but a stop at the dealer to report it may be a good idea. Make them note "operating normally" in their log book (even though I doubt they'll bother taking it on the road). As others have noted, worrying about mid-tier gasoline pricing math and/or trying to ameliorate a possibly imagination-sourced knock issue with gasoline doesn't make any sense. |
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Have you tried buying one of those cheap ethanol test bottles of Amazon? Its pretty basic, just fill water to the blue line, fuel to the fuel line, shake...and see if that water line grows and to where. It will give you your % of ethanol and you can see any crud in it. |
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Does the owners manual state 87 oct? On a side note, I have my second Tacoma, Gen II garage queen (just pull my RV on trips). Got the ECU flashed in March. Horry Shit! Brand new truck. Might want to consider Overland Taylor Tuning. Check out the results on Tacomaworld. Lots of talk about octane. Here My 2014 was getting 10/11 MPG while towing a 2250lb RV (I have tow package rated to 6400/650 lb). I now get 13/14, no gear hunting, excellent throttle response. The dyno isn't overly impressive, but the throttle and trans mapping is worth the $$$ alone. Torque ~+15 ft/lb, HP ~+ 10/12. The 4.0 is a rock of an engine but rated around 235 HP stock. OTT |
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Originally Posted By outdoorgb: Does the owners manual state 87 oct? On a side note, I have my second Tacoma, Gen II garage queen (just pull my RV on trips). Got the ECU flashed in March. Horry Shit! Brand new truck. Might want to consider Overland Taylor Tuning. Check out the results on Tacomaworld. Lots of talk about octane. Here My 2014 was getting 10/11 MPG while towing a 2250lb RV (I have tow package rated to 6400/650 lb). I now get 13/14, no gear hunting, excellent throttle response. The dyno isn't overly impressive, but the throttle and trans mapping is worth the $$$ alone. Torque ~+15 ft/lb, HP ~+ 10/12. The 4.0 is a rock of an engine but rated around 235 HP stock. OTT From the owners manual: “Fuel information You must only use unleaded gasoline. Select octane rating 87 (Research Octane Number 91) or higher. Use of unleaded gasoline with an octane rating lower than 87 may result in engine knock- ing. Persistent knocking can lead to engine damage. At minimum, the gasoline you use should meet the specifi- cations of ASTM D4814 in the U.S.A.” It does sound noticeably better running on 89+; at the operating range that I suspected knocking is not as noticeable. There is a dissonance in that range before it up shifts, but not the harsh metallic rasping when running regular 87. I was able to capture some limited timing data, and timing was around +10 to -14 when the “knock” was present. I need to repeat that with the higher octane. |
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^^^ My 2014 has similar wording about octane in the OM. I have been tempted to run higher octane when I tow (which is mostly why I do) but interweb research shows different schools of thought on this. I am not an expert on the topic. One thing I am convicted about, if it knocks at 87 and not at +87, I will use a higher-octane gas until I knew the underlying problem. |
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Originally Posted By MJ11B4P: From the owners manual: “Fuel information You must only use unleaded gasoline. Select octane rating 87 (Research Octane Number 91) or higher. (R+M)/2 If the R has to be 91, you probably want at least an 89 marking on the pump. (if my math maths correctly)  
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Originally Posted By NAM: (R+M)/2 If the R has to be 91, you probably want at least an 89 marking on the pump. (if my math maths correctly) https://i.imgur.com/3C3d4v5.png Originally Posted By NAM: Originally Posted By MJ11B4P: From the owners manual: “Fuel information You must only use unleaded gasoline. Select octane rating 87 (Research Octane Number 91) or higher. (R+M)/2 If the R has to be 91, you probably want at least an 89 marking on the pump. (if my math maths correctly) https://i.imgur.com/3C3d4v5.png You lost me. The big number is the select octane rating (anti-knock index). |
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Originally Posted By Bohr_Adam: You lost me. The big number is the select octane rating (anti-knock index). The big number (the Posted Octane Number) is the AVERAGE of the Research Octane and the Motor Octane Numbers. His manual stated "Research Octane Number 91". He reports issues with a posted octane number of 87. We don't know what the two numbers actually are, only what they average out to when combined. My hunch is that the Research Octane Number of the 87 blend isn't 91. Of course, I could be totally wrong; just mathing the math. |
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Originally Posted By NAM: The big number (the Posted Octane Number) is the AVERAGE of the Research Octane and the Motor Octane Numbers. His manual stated "Research Octane Number 91". He reports issues with a posted octane number of 87. We don't know what the two numbers actually are, only what they average out to when combined. My hunch is that the Research Octane Number of the 87 blend isn't 91. Of course, I could be totally wrong; just mathing the math. Originally Posted By NAM: Originally Posted By Bohr_Adam: You lost me. The big number is the select octane rating (anti-knock index). The big number (the Posted Octane Number) is the AVERAGE of the Research Octane and the Motor Octane Numbers. His manual stated "Research Octane Number 91". He reports issues with a posted octane number of 87. We don't know what the two numbers actually are, only what they average out to when combined. My hunch is that the Research Octane Number of the 87 blend isn't 91. Of course, I could be totally wrong; just mathing the math. Now you got me curious and wanting to math in public. Anyone who knows me well, knows this is dangerous. Read further at your own discretion. If we assume the RON is 91, in order to reach 87 we'd have to assume a MON of 83. 91+83=174, /2= 87 If we opt to lower the RON to 90, that means we have to increase the MON to 84. 90+84=174, /2= 87 At this point, we have to make assumptions about the MON relative to the RON. I submit that is very rarely closer than 8 points to the RON. For the reported rating to stick, and the RON to be lower than 92, we're looking at only a 6 point spread. Further, the greater the spread, the higher the MON has to be to get the reported rating, I don't think that's likely that we have one a 6 point or less difference between the RON and MON, but I'd need to let someone with a better understanding of fuel chemistry weigh in on this. |
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Modern life is one steep, perpetual tax on the mathematically impaired
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Originally Posted By Bohr_Adam: I don't think that's likely that we have one a 6 point or less difference between the RON and MON, but I'd need to let someone with a better understanding of fuel chemistry weigh in on this. Like you, I have no clue of the chemistry and/or what spreads are considered normal. I was more less trying to point out that was his manual is actually asking for isn't necessarily what the pump say. Not sure if this is accidental mixing of the terms, or intentional obfuscation by the MFG (well sure.. you can use 87...if it's 87 that has 91 RON...which may or may not be 87 PON). I mean, some people may not want to buy a car that "requires" premium, so...they mix up the terms a little bit to make it sound like it's fine with regular. (or again, I could be talking out my ass. lol...who knows). |
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Originally Posted By MJ11B4P: Fuel prices at my usual Texaco are: 87 @ $3.689 89 @ $4.189 93 @ $4.589 If mid-grade is 87 and 93 blended at the pump, then 89 is a 2:1 mix… 67% 87 + 33% 93. The fair price for 89 should be $3.989… if it were 1:1 mix for 90 octane, it should be $4.139. Outside of pricing fuckery, is this standard practice or just my local stations? Or is my math off? Simple. Pump 10 gallons of 87, hang up the pump and then repay and pump 5 gallons of 91. Self blending 15 gallons of your own 89 for $59.835 vs pumping straight 89 for $62.835. $3 dollar savings per tank. At 2 tanks a month, that will save you $72 a year. And for anyone who's going to attack me for indulging, I track my time interacting with the differently enabled by the minute and write it off as a charitable activity on my taxes. 
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Originally Posted By ScooterInVegas: Simple. Pump 10 gallons of 87, hang up the pump and then repay and pump 5 gallons of 91. Self blending 15 gallons of your own 89 for $59.835 vs pumping straight 89 for $62.835. $3 dollar savings per tank. At 2 tanks a month, that will save you $72 a year. And for anyone who's going to attack me for indulging, I track my time interacting with the differently enabled by the minute and write it off as a charitable activity on my taxes. Pump the premium first to maximize the product getting to your tank versus the next customer 
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