By on April 12, 2016

2012 Lexus ES350, Engine, 3.5L V6, Image: © 2012 Alex L. Dykes/The Truth About Cars

TTAC regular PrincipalDan writes:

Sajeev,

With the price of gas dropping to levels not seen in many moons, a thought occurred to me: Many of us are driving around in an average vehicle that has an engine used by another vehicle advertised as having more horsepower and recommending premium fuel.

For example: Toyota’s 3.5-liter V6 powers the Camry and ES350, but the Toyota’s tests with 87 octane fuel while Lexus tests with 91 octane fuel.

Do the manufactures actually bother using different engine programing in these various vehicles? Or is greater horsepower just a premium fill-up away for those with lowlier vehicles with premium antecedents?

I know there is no benefit to using high-octane fuel in an engine not designed for it, and I wouldn’t suddenly put my Highlander on an all premium diet, but I think I’m asking a relevant question.

Sajeev writes:

Manufacturers often use a unique engine calibration for different models using the “same” engine. Justification for a unique part number is in the eye of the beholder, but occasionally unique engine parts need a unique engine calibration. Peep the 32-valve mill in the Lincoln Mark VIII vs. the Cobra offshoot, or more recently the LSA vs. LS9 story. I don’t expect this from a Lexus ES vs. Camry V6 comparison; it’s named entry-level luxury for good reason.

For the ubiquitous Toyota 3.5-liter V6, the Lexus ES has not required premium fuel since Toyota implemented direct injection, so I went back in time. The (non-direct injected) 2010 ES burns premium while the 2010 Camry consumes regular. The benefit? An extra four horsepower and an extra six pounds-feet of torque at the same revs over the Camry.

Such a power bump is totally worth the bragging rights, and the extra cash spent at every fill-up. Or not.

Unique tunes help computers make the ideal vehicle for whatever need, while saving money by re-using parts. Perhaps the Lexus’ engine calibration has smoother transmission shifts, integration of more tech, etc.

What say you, Best and Brightest?

[Image: © 2012 Alex L. Dykes/The Truth About Cars]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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78 Comments on “Piston Slap: Fuelish Thoughts on Engine Calibration...”


  • avatar
    JimZ

    changing the airflow (either exhaust or intake) usually requires a re-calibration, especially if it has speed-density (MAP + IAT) engine management.

  • avatar

    The ES350 calibration could be something as simple as running more timing to extract a little extra power. It probably has an additional calibration or adjustment similar to the Camry to fall back to if it sees knock from a driver filling up with lower octane fuel.

    My guess is that there is no power benefit to filling up the Camry with premium fuel since it probably does not have the mapping to advance the timing like the Lexus does in order to pull out the extra power.

    • 0 avatar
      Wade.Moeller

      This is most probably correct. Turn up the timing, turn up the power. This is why you get more power out of alcohol. It’s much greater octane rating allows for much more advanced timing which results in more power out.

    • 0 avatar
      porschespeed

      True, The Camry map may not have the ultimate extra one degree or whatever it is on the Lexus to allow the extra power.

    • 0 avatar
      derekson

      They might just run the same calibration with the ECU retarding timing on 87 octane, and the Camry was tested and rated running on 87.

  • avatar
    porschespeed

    It advances the spark until it detects knocking/pinging, then backs it off just a fraction of a degree. Wash, rinse, repeat. LH Motronic from the ’90s was capable of adjusting every firing pulse. Today’s systems are better.

    So yes, you’re losing power. Not a boatload, but some. Haven’t gotten to really dig into Toyota electronics (the few I’ve done I’ve just replaced with Megasquirt). Pretty much all system work the same way. The cars that are E85/flexfuel do have an inline sensor to determine the fuel and select the appropriate injection map.

    • 0 avatar
      highdesertcat

      Yeah, I’ve often commented on how there is a noticeable difference running Premium Unl over RegUnl in all my cars, even my 1989 Camry V6.

      Topping off with E85 in my two 5.7L Toyotas does cause a change in spark timing until the right balance is reached to prevent knocking/pinging. And until that balance is reached, the loss of power is noticeable, requiring a lot more pedal to make the vehicle go.

    • 0 avatar
      Scoutdude

      Flex fuel cars haven’t had a physical fuel composition sensor for over a decade.

      Now a number of manufactures just let the computer adjust via fuel trim. Toyota and Chrysler are in this camp and it is why they have crappy performance and mpg on E85. They are capable of running on E85 but they are not designed to run on E85.

      Now Ford and GM vehicles on the other hand use a “virtual FCS” algorithm that senses a refueling event and infers the E% in the initial driving following the event. They then use that to select the proper timing curve as well as filling in the timing trim table. They are designed to run on E85 and because of that they make more power on E85 and their mpg does not suffer as large of a drop as would be indicated by the lower energy content per gallon.

      Very few cars have adaptive timing. Yes they have knock sensors that will retard the timing when it senses knock but they will just respond by pulling out a fixed amount of timing and often quickly revert to the standard curve. They do not use that data to fill a trim table and learn the octane of the fuel currently in the tank.

      • 0 avatar
        highdesertcat

        It’s always educational to read your comments. Thanks.

        • 0 avatar
          CoreyDL

          I wonder if he’s an engineer at the EPA or something.

          • 0 avatar
            highdesertcat

            No. He told us where he works a long time ago, but it’s not up to me to repeat it.

          • 0 avatar
            Scoutdude

            No I’m not an engineer, though I do teach engineering to high school students via teaching them how to build robots.

            I did spend a couple of decades as a mechanic and near the end diagnosing driveability problems, particularly those that do not set engine codes was one of my specialties. So yeah I tried to keep up on the latest tech and still have subscriptions to trade publications, even though I gave up working on cars as a job several years ago.

          • 0 avatar
            CoreyDL

            Ah ha, thanks. You always really know your stuff.

      • 0 avatar
        tonycd

        A question for my education:

        There was an extensive thread on this topic a few years ago on Acurazine. I started it by asking, “Okay, my V6 is rated ‘premium fuel required’ (not merely “recommended for maximum performance,” the usual phrasing). So, will running regular actually harm my engine?” I got a blizzard of replies, including one from a guy who sounded as if he knew much better than I what he was talking about. He heatedly contended:

        “YES it can damage your car. More specifically, your EVAP system and/or your catalytic converters. On some cars using low-octane fuel will set a fault code and sometimes it means the charcoal canister has taken a crap.

        “And guess what, because the dealer found out that your knock sensor wasn’t faulty, they can probably track it down to low-octane fuel thanks in part to misfires in every cylinder and deny your warranty claim. Ouch. Now your car probably won’t pass smog either, if you have it in your state.”

        True? False?

        • 0 avatar
          White Shadow

          The only way the cat will get damaged is from extensive misfires, which will send unburned fuel through them. So if he’s equating the use of low octane fuel with misfires, that’s mostly incorrect. Low octane fuel can cause pre-ignition (also known as ping or knock), which can cause a small amount of unburned fuel to get into the exhaust. But in reality the knock sensors will retard timing and prevent any negative effects. The engine will lose a bit of power, but nothing really noticeable. The EVAP will not be affected by running low octane fuel.

        • 0 avatar
          Scoutdude

          The idea that it will damage your evap system is pure BS.

          Before the advent of the knock sensor yes using too low of an octane could damage your engine because of the detonation that would occur. I guess if you drove to the point where it started causing serious dmage to the engine, IE the piston coming apart then maybe if you continued to drive it if you could then the catalytic converter could also be damaged.

          So yeah pure BS on any halfway modern car.

      • 0 avatar
        porschespeed

        Didn’t know they had done away with the physical sensor, but it’s no shocker. I’m familiar with things that are generally Bosch and at least 10 years old. As I noted, there are better things today.

        I an surprised that adaptive timing has been abandoned. The whole point is efficient combustion, and that tilts right on the edge of pinging. As that point is always slightly variable with IAT, RPM, load, etc, why would one abandon getting right to the edge and then backing off 1/10th? Perhaps I wasn’t clear, for instance even 25 year old LH Motronic, the basemap is deliberately set up advanced, then the system retards if there’s a knock. Then listens, and retards another fraction, if it hears it again. If it doesn’t hear knock, then it puts it back in until it does.

        Thankfully, I don’t have to meet OEM EPA regs, just have customers pass the state sniff. 16X30 tables and let the math populate the steps between is all I have to program.

        • 0 avatar
          Scoutdude

          Adaptive timing has not been abandoned it is just still far from universal.

          What you are describing with the Bosch system is not adaptive timing it is active knock control.

          With true adaptive timing, which was first introduced on North American vehicles by Ford there is a long term timing trim table where the timing is “learned” just like long term fuel trim.

          With many of the early vehicles that were equipped with knock sensors the system was designed to pull out a fixed amount of timing for a fixed period of time. It would then return to the standard timing curve.

          On early small block Chevy engines this meant that adjusting the valves could have a huge impact on the power the engine made. The knock sensor would often interpret the valve clatter as knock so essentially the vehicle would always operate with that fixed amount of timing retard. Adjust the valves and the increase in power and mpg could be significant.

          • 0 avatar
            porschespeed

            No, what I’m describing with Motronic is adaptive timing. It’s not knock control, it continually seeks the most advanced spark without knock, therefore, it adapts.

            There is no such thing as “long term” timing trim – every frakkin’ tank of gas you buy has a *slightly* different octane, the suggestion that field can be learned and populated is absurd. Somebody may have told you it can happen, but in reality, it can’t. It’s continually relearned.

            Once again, I’ve explained to you how even early Motronic works, that you don’t know/understand is not reflective of actual reality. Motronic pulls it out until it quits knocking, and then puts it back in until it does. That was part of the computer varying the map, to fill the spaces in between the hard points.

            That there was some junk built without using Bosch patents is irrelevant, the fact is that everything Ford (and most of GM/Chryco) has ever done with EFI has been a Bosch licensed development, or based on Bosch design is kinda the point.

            Adjusting the valves on Chebbies is indicative of the inherent problems of OHV, not a problem with EFI. Only Chebbies implementation of it.

  • avatar
    TDIGuy

    So the performance difference really isn’t worth the extra $ *most of the time*. And the reason I emphasize that is: What happens when you come back with a warranty claim that the dealership can blame on the fuel? Are they going to say “well, you didn’t use premium fuel, so no warranty for you”?

    Glad this article came up today. Since a certain writer here always seems to like Lincolns, I was looking at some performance numbers on one yesterday. There was a note under the HP and torque, and most likely the 0-60 numbers: “Measured using 93 octane fuel”. Really? Many, dare I say even most stations around here don’t even sell that stuff.

    • 0 avatar
      Land Ark

      They don’t sell 93 near you? Where is this so I can avoid it?
      My car requires 93 because of the Cobb tune. I’ve yet to find a gas station near me that doesn’t sell it. I’d be SOL if I were away from home and stations didn’t have it.

      • 0 avatar
        derekson

        Lots of states top out at 91.

        • 0 avatar
          TMA1

          I think 91 is tops in the western states, while we back east get 93. I’ve found that most Sunocos in Virginia have 91 and 93, and I’ve found one in Maryland that has both as well (my MX-5 prefers 91). I don’t know of any other brand that carries it around here.

          • 0 avatar
            28-Cars-Later

            I recall seeing 93 in Las Vegas at least once in the three times I filled up there.

          • 0 avatar
            sgeffe

            93 is the prevailing Premium gas in Ohio.

            You pay $0.40+/gal. over the increasing cost of Regular (87-octane) for that privilege, however.

      • 0 avatar
        TDIGuy

        I tried to do a search on Gasbuddy, but 93 octane or super premium isn’t an option you can search for. I think Sunoco and Shell sell it around here, but again not everywhere. The further I Get away from Toronto the harder it is to find.

        Actually, one of the big oil companies, I think it was Shell got themselves in trouble a while ago for saying that using their premium gas will give better performance and mileage. Since that was only true if your car was actually designed to take premium fuel they have since changed it to “runs cleaner”, which is true in the sense that their premium fuel has more detergent in it.

      • 0 avatar
        Jagboi

        Depends on where you are. 91 is the most I can buy. Octane requirements decrease with elevation too, so if you live in Denver your car doesn’t need as much octane as the same car in Seattle.

        I’ve seen 94 at Chevron’s in BC.

        • 0 avatar
          VoGo

          In MA, the gas stations sell only 87, 89 and 93. It’s as if they skipped 91 on purpose, to force people who need 91 to pay extra for the 93.

          As if. Strange how when we allowed Exxon to buy Mobil that gasoline retailing suddenly got a lot more profitable.

          • 0 avatar
            highdesertcat

            In my area, and most of my region, all they sell everywhere is 86, 88 and 91, all of them E10; also some E15 and E85.

            But that could be because of the altitude (continental divide) and the proximity to the ethanol makers.

            But ever so often while on the road out of my area, I run across a gas station that sells 93 PremUnl. That’s when I fill up with as much as I can.

            I usually carry four empty 5-gal gas jugs with me for when I cross into CA, to bring the cheaper gas with me from AZ.

            If those gas jugs are empty at the time I spot a station selling 93, I fill them up, as well as the truck’s gas tank.

            93 is a rarity in my area.

          • 0 avatar
            Sigivald

            … why stock up on 93?

            I mean, do you own a vehicle that has an engine tune that can actually *use* that extra knock prevention?

            (Now, “saving CA gas tax”, I totally understand…)

          • 0 avatar
            highdesertcat

            Sigivald, not stock up to keep on hand, but stock up in the sense of carrying an extra 20 gal of the highest octane gas I can find to use during my trip.

            Sometimes when on the road, the gas that you get is not always what is advertised, i.e. selling RegUnl in the Premium pumps. It’s been known to happen, but who is going to make a U-turn on a long trip to make an issue out of it?

            All of the engines I own will run on 85-octane, some better than others. Putting in the highest octane where I can reduces the occurrence of slothiness in my vehicle, even in my 1989 Camry V6.

          • 0 avatar
            Scoutdude

            It can totally suck buying gas on a road trip. Several years ago I was taking the family on a summer road trip. At one point it required turning off the interstate to traverse the local 2 lane for something like 150 miles before any town of consequence. I had intended on buying gas in the last big town before the point it was time to get off the interstate even though I was several miles away from actually needing gas. I didn’t realize that I had passed it until a fair distance after. So when I pulled off the interstate to head down the 2 lane I fueled up at the little sketchy station there. I went on my way and made it to our destination for the night. The next morning we headed out and on the way out of town up a good grade the vehicle all of a sudden wouldn’t go over 30-35mph. I turned around and headed back to town. It seemed like the classic plugged fuel filter so I found the nearest parts store and picked up a filter. Since it was under the car I inched one end up on the curb and slid under the car and replaced it. I had full power again and headed off with only a small delay. The next day heading down the interstate it started slowing again. We pulled into the next town and found a K-Mart that was closing in a few minutes. Thankfully they had the right filter and I did the drive up on the curb thing once again and we were on our way. It wasn’t too much longer until it happened yet again. This time I stocked up on them thankfully because the next time it happened I was in the middle of no where. That time I drove part way across a shallow ditch to gain access. All told I replaced the filter 5 times on that trip before making it home. Last time I checked I still have a filter for that vehicle somewhere in the garage.

            So yeah I’m very careful on where I choose to purchase gas when I’m away from home.

          • 0 avatar
            highdesertcat

            Scoutdude, I can totally relate. I had something similar happen to me about 20 years ago coming back from a Racing trip at Grand Junction, CO.

            We topped off the gas tank in my ’88 Silverado at an Amoco gas station in Grand Junction before heading south toward New Mexico by way of Delta, Montrose, Ouray, Silverton, etc, with the trailered race car in tow.

            When we got to about 20 miles north outside of Cuba, NM, the Silverado began to run really, really bad, until it died.

            Long story short…… too much water in the gasoline.

            We filled up the truck’s gas tank from the spare jugs I always carry that still had NM gas left over in it for the race car, and limped into the nearest gas station in Cuba. Tense moments.

            A couple of yellow bottles of “Gas Dry Alcohol” in the gas tank along with the remaining 110/115 AVGAS of the race car, and the old Silverado was beginning to run like it’s old self again.

            Lesson learned.

  • avatar

    Good Question.

    I just got done going over endless threads on this topic. The 3.6 liter HFV6 in the Caddy says “regular fuel”, but as a DI engine with high compression, you’d think put in premium.

    After too much google-fu, finally in a camaro forum, I find that the LLY engine has two maps, one high octane and one low octate. My LLT engine has one map, for 91 octane, but you CAN run regular all day. Folks with engine analyzers state that the engine retards the spark more often with the lower octane….so, you can run it all day on regular OK, but it is happier with high octane. Supposedly the regular gas OK was a marketing tool.

    If your ES has only a low octane map, then nothing will happen. If your car is actually tuned for more, then you might find some extra. I find the Caddy responds quicker to throttle and hits harder at high RPM.

    I’ve chipped a few cars over the years. The result really depends on how the OE chip was tuned. My E46 is already optimized for high test, so there isn’t much you can do there.

    Fill the car with premium for two or so tanks then toss in some octane boost, and see what happens. Turbo cars have it easy…chip tune means more boost, but for NA cars, …it depends…

    • 0 avatar
      derekson

      This is not uncommon from what I’ve found. The VW 2.5L is the same way: it was tuned originally for premium but the ECU can retard timing and run on 87 octane fine, and for marketing reasons they labeled it as recommending regular.

      • 0 avatar
        Kyree S. Williams

        I’m surprised the 2.5-liter I5 is capable of taking premium. It is arguably one of Volkswagen’s most solid engines…ever, and was only recently discontinued.

        The 2.8-liter VR6 in my Mk.3 Jetta recommended premium, and was noticeably unhappy with anything less.

        • 0 avatar
          derekson

          I read an article where they actually dynoed one on premium vs regular and it was like 6 or 7 HP and TQ at the wheels, plus 1-2 MPG better on 93 octane. That’s not a bad gain on an engine that makes 170 HP.

  • avatar
    nels0300

    I have a 2014 Camry V6 and had a 2009 Lexus ES and have read everything there is to read about the 2GR-FE engine on the internet.

    There is a huge thread on Club Lexus discussing this with a few Lexus techs chiming in saying it’s the exact same engine with the same ECU. The ECU adjusts for whatever octane you’re using.

    People doing 2GR-FE swaps into MR2s have found the same thing, same power whether using the Camry computer or the ES computer.

    So, the ES350 has 268 hp on regular, and the Camry V6 has 272 hp on premium, and vice versa.

    • 0 avatar
      VoGo

      Hold on there, the Lexus dealer told me that there are magical Lexus gnomes at the factory making sure that only the Lexus vehicles get the extra special Lexus engines. The look the same on the outside, but inside, you can really appreciate the relentless pursuit of perfection.

      He wouldn’t lie about that, would he?

      • 0 avatar
        28-Cars-Later

        I tried to hire the magic Lexus gnomes, but their union had too many demands.

      • 0 avatar
        nels0300

        Well, he’s somewhat right.

        They might look like magical gnomes because most of them are shorter than the average American, but the builders of the Lexus 2GR-FE in the ES350 are actually just Japanese people and robots.

        The 2GR-FE engine in my Camry however was built by Bobby Joe, Cletus, and a robot in Kentucky.

      • 0 avatar
        Quentin

        It is possible to build the same product and hold it to different standards. Maybe a certain machining spec on the block makes a quality product but the noise is higher. You can design the manufacturing process so that parts not meeting the highest spec don’t make it to the luxury product. You can pay your vendors more money for a different bearing on a water pump when checking for noise because it is going to go into a BMW instead of a MINI and the BMW customer is more likely to hear the noise than the MINI customer. Yet, the engines may still get the same basic designation from the manufacturer or their internal drawings call out that you can use one part number on both vehicles but the other part number is only allowed to be used on the MINI.

        The fact that ES350 was built on the other side of the planet versus the Camry V6, odds are that different suppliers were supplying the components to the assembly plants. Different suppliers = different drawings = different specs. I’d imagine that Toyota would push for it to be as similar as possible because that reduces part numbers to stock and such, but them being different isn’t outside the realm of possibility.

        • 0 avatar
          nels0300

          They could be different, but Toyota’s major suppliers, like Aisin and Denso, also have North American operations.

          I’ve had both the ES350 and Camry V6, the only difference I could tell was the engine cover.

          • 0 avatar
            highdesertcat

            “I’ve had both the ES350 and Camry V6, the only difference I could tell was the engine cover.”

            That’s really all the difference there is, unless the air-intake and exhaust system of a Lexus is less restrictive.

            Better breathing makes for more power over a wider band.

          • 0 avatar
            tonycd

            A guy posted on Club Lexus who had just recently gone to work for Lexus in America. He sounded honest, and insisted he’d personally witnessed that the ES was built entirely — as in 100% of the parts in the car — from parts and assemblies imported from Japan. He also insisted that when he had examined an ES and an Avalon side by side, one could readily detect that the small parts throughout the car (think latches, handles, hinges, trim) were of higher quality on the ES. He sounded sincerely gee-whiz impressed with all this. It wasn’t obvious that he was acting.

            I have read that Toyota views it as policy to hold all Lexus models to a generally higher standard of component and assembly quality than those badged as Toyotas. So this isn’t unbelievable to me (and no, I’m neither a Lexus owner nor a Lexus fanboi).

          • 0 avatar
            highdesertcat

            ” insisted he’d personally witnessed that the ES was built entirely — as in 100% of the parts in the car — from parts and assemblies imported from Japan. ”

            I can believe that. Lexus is Toyota’s flagship. Heaven forbid the quality of Lexus should fall to that of the North American-made Toyota products assembled with parts made by North American suppliers.

            These NA suppliers make the same parts used in Ford, GM, and Dodge products, with all the resulting quality issues that follow.

            That’s why many old-school Toyota owners insist they will never buy another Camry made in NA. It’s no better than anything from Ford, GM or Dodge.

            My best friend is one of those, and I’m driving his 1989 Camry V6 now.

    • 0 avatar

      That makes sense. It isn’t like the car suddenly gets 500 hp, but it just feels smoother on the high test.

      I’ve had my Acura dealer insist on a receipt for gas when you return loaners….to show you didn’t put regular in the car, not to back up the gas gauge. I’ve always put premimum in my Acura…I wonder, I’m not a Honda geek, if the same engines are the same and/or have different octane Acura vs. Honda.

  • avatar
    PrincipalDan

    I know it is really just mental mastur… but it is an interesting thought experiment. Does one of the B&B know if Cadillac actually made any changes to the Northstar when they switched from saying “Premium Fuel Only” to “regular”? I believe that happened at some point in the 00s.

    • 0 avatar

      The 2001 Deville is rated for Premium while the 2002 is rated for Regular.

      As far as I can tell, they both have the same part number for a complete longblock and both use the same 12573503 ECM but the calibration could be slightly different or they might have just relied on the built in knock control to retard the timing.

  • avatar
    maxxcool7421

    A GREAT deal of the HP and TQ disparity comes in with the Lexus units having ds-4 injection/heads and or BOTH port-injected *and* ds-4 injection. After that it is up to vvt-i..

    case in point the 300+hp is350 utilizes both ds-4 plus vvt-i. where as my wifes 270hp Rav4 does not.

    • 0 avatar
      nels0300

      Not all of the Lexus 3.5Ls have DI, Lexus also uses the 2GR-FE with port injection.

    • 0 avatar
      Quentin

      The cars in question are 2GR-FE equipped ES350 and Camry V6 which is only port injection. The IS350 is a 2GR-FSE with the dual injection.

      Until the 2016 RX350, all FWD 2GR engines were the FE variety with only port injection. Eventually ES350 will transition over to the dual injection RX350 engine, but it remains port injection at this point.

  • avatar
    ponchoman49

    That’s interesting on the GM 3.6. I wonder how the LFX is in my Impala. Never tried anything other than 87 octane fuel so I will have to check that out with a couple of tanks of premium. We have the choice of 93 octane with 10% ethanol or non ethanol 91 octane.

  • avatar
    cbrworm

    What I have seen is that frequently there are physical differences, sometimes just plumbing, other times mechanical changes within an engine code umbrella.

    BMW makes changes to their engines of a set displacement to increase or decrease power based on model.

    Nissan’s old VQ35 and VG30 had different submodels based on car configuration and expected use. With the VQ35DE, there are at least three different power variants that I know of that are all called VQ35DE, they are mechanically different from each other. One requires premium fuel, the others recommend it.

    • 0 avatar
      Kyree S. Williams

      That’s interesting. I though the only differences were between the VQ35DE and the VQ35HR, the latter of which tended to be used in longitude applications, and mostly for Infiniti products. I did not know there were variants within the VQ35DE—which our 2005 Murano had, in some form or another.

  • avatar
    Kendahl

    My 2008 Infiniti G37S is supposed to run on premium with a minimum octane rating of 91. Last summer, I decided to try 89 octane midgrade because it’s so much cheaper than premium. The car runs fine on it. I’m probably losing some power at full throttle, especially during hot weather, but the difference isn’t obvious. So far, I haven’t tried 87 octane.

  • avatar
    Vetteman

    My wife’s 2006 Lexus GS300 with 55 K on the clock is according to Lexus to be fed premium 91 or higher Since we live at about 2600 feet above sea level I have tried just running regular and it work just fine . I really can’t tell any difference in performance . The strange thing is she gets 26 to 27 miles per gallon on the premium and 29 to 30 using the 87 octane regular. I have to assume the more volatile lower octane produces more power thus less power needed to move the car down the road for a given quantity of fuel. I have seen this happen for many years as we have had the car now eleven years . I have not seen this in other cars I have owned . This V6 is toyotas first gen direct injection that only has one injector per cylinder not the later ones with a second injector per cylinder in the intake port of each cylinder runner.

    • 0 avatar
      CoreyDL

      “The strange thing is she gets 26 to 27 miles per gallon on the premium and 29 to 30 using the 87 octane regular.”

      Rubbish.

      “I have to assume the more volatile lower octane produces more power thus less power needed to move the car down the road for a given quantity of fuel.”

      Rubbish.

      Science is your friend. But maybe you’re Norm’s cousin.

      • 0 avatar

        This is mom’s foot vs yours, not the octane. We did a cross country trip in an Acura MDX. Mama’s tanks were all over 20 mpg. Mine were more 18 mpg, max. Mom is 10 mph slower and a lot smoother.

        If I use cruise control and stick to it, I get 21 mpg. Smooth counts for a lot in MPG.

  • avatar
    55_wrench

    I experimented with this on our LS430 right after we bought it late in 2014.

    Factory said to use only high octane fuel, but I used 87 or 89 around town when we first got it ..just to see if it could manage without the 91. Right after we bought it we took a 4000 mile road trip, and the best mileage we got on the entire trip was on a tank of 91 octane, and that while climbing the Continental divide. Fully loaded, it got 26.6MPG at posted speed limits of 70-75 the whole way.

    I’ll resort to midgrade around town, but it now gets 91 anytime we take it on the road.

    FWIW the engine management responds very well to varying fuel conditions. I have yet to hear any preignition knock. Not even once. Ditto for the 3 liter V6 in the 2001 Avalon I used to have.

    • 0 avatar
      Sigivald

      Their owners’ manual language (I looked up the ’06 – http://drivers.lexus.com/t3Portal/document/om/OM50703U/pdf/sec_06-01.pdf) is … nice.

      “Select premium unleaded gasoline with an Octane Rating of 91 (Research Octane Number 96) or higher for optimum engine performance.”

      Combined with “If premium fuel is not available, you may temporarily use unleaded gasoline with an Octane Rating as low as 87 (Research Octane Number 91).”

      I read that as “it will run 87 octane … honestly, forever … just fine, but don’t complain if it knocks a little or it’s not as zippy”. (Other notes in the manual there said some knock under acceleration was normal.)

  • avatar
    CoreyDL

    I tried this once, in an I30 with the VQ30 engine which mandated premium fuel. After owning it a while and using 93, I thought eh let’s see what happens on regular.

    It ran rough, and was down on power. Didn’t like regular fuel at all. I don’t even think I let it get down to 1/2 a tank before filling back up with 93, it was that bad.

    • 0 avatar
      highdesertcat

      “It ran rough, and was down on power. ”

      Yup. Happens to me in my cars too, whenever I change the octane of the gas I use (while I’m traveling out of my area).

      As was explained in another thread, another time, the engine management computer of my vehicle has a an apoplexy and has to adjust to the volatility of the fuel, dialing back air/fuel mixture and spark timing.

      I knew it was real because I could feel it in the performance of the vehicle, no longer giddy, more like a five-toed sloth, when I jump on the go pedal.

      • 0 avatar
        PrincipalDan

        One of my relatives was moving from Thoreau, NM (roughly 7,000 ft in elevation) to Laughlin, NV the descent in to Laughlin drops you precipitously in altitude until you reach 588 ft and the Colorado River.

        He always said his vehicles didn’t run right for a day or so when he was doing the frequent trips back and forth. I always just chalked it up to the huge drop in altitude and the engine management computer trying to figure things out.

        • 0 avatar
          highdesertcat

          Thoreau, NM. Know the place well. Had a very dear friend, and his wife, who both taught (and coached sports) at the school system there for many, many years, a long time ago.

          After he retired from that school system, they both moved to Henderson, NV, where they took up teaching again, and are still doing so to this very day.

          And we both experienced those same gremlins when we helped him move from Therrrooooo.

        • 0 avatar
          dal20402

          If he had high-altitude fuel the octane may have been too low for low-altitude conditions. At high altitude the options are typically 85/87/89 instead of the usual 87/89/91.

    • 0 avatar
      dal20402

      Same experience with the Subaru EJ255 turbo in my ’13 Forester, which says “PREMIUM FUEL ONLY” on the gas cap and dash. I put in 87 by accident. Even in cool weather, the engine was obviously unhappy, with audible knock and obviously pulled timing.

  • avatar
    JustPassinThru

    In my shadetree-wrenching experience, which ended as FI became the standard…premium-fuel stipulation came from high-compression specifications. In those dying years of carburetion, there were engines made to run a fine line, where 89-octane regular was stipulated but occasional engine ping would penetrate the Tears-For-Fears playing on the tinny factory speakers.

    Switching to 91 usually stopped it. Cut driving time down, too – more cost-per-mile equals less miles-per-week.

    Just dumping premium fuel in there, does not, IMHO, translate to better performance. I had tried this years ago with a K-Jetronic-powered VW Fox; and later with more-sophisticated FI products including a Wrangler and several Tacomas. No appreciable difference – except in the cost of fill-up.

    If the modern techno-mechanics find me wrong here, feel free to correct.

  • avatar
    285exp

    I have a 1997 ES300 that I’ve owned from new. The owners manual states 87 octane required, 91 recommended. The 1MZ-FE engine is rated at 200 hp. The 97 Toyota Camry used the same 1MZ-FE engine, but rated at 194 hp. It’s owners manual also states 87 required, 91 recommended.

    I’ve always used 87 in mine. A couple of years ago, after one of those regular vs premium debates on a Lexus forum, I decided to try it out for myself. I use this car primarily for commuting to work, same route, same speeds, same time of day, so my mileage is very consistent, excluding mostly highway trips it averages around 20.5 mpg. For the last 4 tanks before switching to 91, 1188 miles, I averaged 20.7 mpg. For the next 4 tanks I used 91, 1215 miles, and averaged 21.2 mpg. For the next 4 tanks using 87, 1226 miles, I averaged 20.6 mpg. Overall I got about 2.6% better fuel economy using 91, though I doubt it is statistically significant difference. At that time, 87 was around $3.30 and 91 was $3.70, about 12% more for 91. Today 87 was 1.89, 91 was 2.29, about 20% more. I did the same thing a few months later, with close to the same results, about a 2% increase with 91. I tried it again later with E0 89 instead of E10 87, with similar results; slightly better fuel economy, but not nearly enough to offset the increase in price.

    The engine doesn’t feel any smoother on 91, or the car any “peppier”, and it doesn’t get enough better mileage to offset the extra cost. I suspect that some of the folks who believe their cars run much better using premium wouldn’t be able to tell if they didn’t know what was in it.

    Your mileage may vary.

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