By on October 1, 2015

Mark writes:


Thanks for the recent advice on winter tires & wheels for my new Focus ST. I took delivery of the car two weeks ago and I’m having a blast. The first thing I did when I got it home was take Bark M’s advice and sign up for the Octane Academy.

So here’s another question: What’s your take on fuel octane and the ST?

I’ve been running 87 octane per the owner’s manual and will probably continue for another tank or two, recording fuel consumption each time. Then I’ll switch over to 93 for a few tanks to see how mileage and performance stacks up. Everything I’ve seen says 93 will only give a 5 hp bump, so I rather doubt premium will be worth the extra cost in the short term.

But what about the long run? Do you think this turbo engine will be happier/cleaner/longer lived by running the expensive stuff?

By the way, I may order a set of tunes from Torrie, just like I did for my Mustang a couple years ago. I don’t know if that will make a difference in the questions above, but I wanted to make sure I mentioned it.

Thanks again!

Sajeev answers:

I’m kinda shocked that going from 87 to 93 octane only nets 9 hp with no change to peak torque according to Car and Driver. Anything is possible with modern computers and their numerous fuel and spark tables. So I recommend the 87 octane and oddball 17-inch Ford winter wheels for maximum hipster ironic-ness. The forum junkies will hate you for it!

Will this hurt you in the long run? I doubt it. Today’s computers are smart enough to keep that from happening. The dyno video above shows how the computer kills timing on the 87 octane tune — a fantastic reason to save money. It also shows how the FoMoCo factory tune is Dick Cheney conservative; easy on the environment, durability and fuel economy.

So why would you run 93 octane — ever?

One reason: The aftermarket tune.

When you get Torrie’s electro-goodness sprinkled on the ST’s computer tables, you’ll want to run 93 and never look back. I bet the aftermarket makes a great 87 octane tune that’s still safe but spicier than stock. However, if such a tune on my 2011 Ranger can net gobs more torque below 3,000 rpm (four-banger, mind you), it’s likely to happen on an ST. It all depends on the quality of the tune and the tuner behind the computer.

What say you, Best and Brightest?

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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23 Comments on “Piston Slap: Focusing on Turbo 93 Octane Tunes?...”

  • avatar

    I have a motorcycle that is rated for 87, but I put 93 in it. I have never had it dyno’d, but the butt dyno indicates peak power gains are minimal. Where the difference comes is at low RPM, high load (i.e. accelerating after a slow down in top gear, or pulling out of a corner without downshifting). With 87, it would knock and buck and just be overall nasty and slower. With 93 it rips pretty much off idle WOT, which probably isn’t advisable but is fun as hell to do and gives me more options. Part throttle response is smoother too.

    Is it worth the cost? IDK. I have been averaging about 3000-5000 miles a year on my bike, and it gets 45 MPG on my commute. I think mileage improves on 93 but I don’t want to do a tank of 87 to find out. But it’s worth it to me. I would look into getting a 93 only tune. It will run better and make a lot more power.

    • 0 avatar

      @sportyaccordy: what kind of bike is that?

      I have an ’06 Yam FJR and it’s apporved for 87. I can’t remember the last time I ran anything else. If you have an FJR and are seeing that much difference, I might have to try the 93.

  • avatar

    The only effect upping the octane in a modern engine is the ECU will advance the timing. The more advanced the timing can be adjusted, the more power the engine can produce from each bang. The amount of the increase will depend on the current tune. Commodity cars will have a tune that often leaves much power untapped. Manufacturers do that to both hit fuel economy targets and to lengthen the life of the motor. They will see a significant increase in power with a tune and higher octane. They will see a much smaller increase with no tune and just higher octane.

    There is a maximum advance either in the programming or in the capability of the ignition system. There is also a maximum retard to be used when the octane is low.

    If you use a low enough octane rating, the ECU cannot compensate and you’ll end up with pinging/knocking and that will break your motor before it’s natural life is over.

    If you use a high octane, when the ECU hit maximum advance, nothing bad will happen.

    Any car not intended for use on a track will have no need for higher then recommended octanes. When you put a different tune in, a reputable tuner will have a new recommendation for the octane.

  • avatar

    My recent experiments with reg vs prem fuel.
    In our golf/lake community we have a gas station that recently added a marine fuel (91 oct) to its tanks. Although in some states you are not allowed to use marine fuel in cars. it seems no big deal here in our area.
    Everybody does it.
    I decided to try it in m MKS 3.5 turbo.
    The MPG went from and average of 22.3 to 24.3…with a 60 country/40 urban drive. This is a big deal and shows all the MKS haters this big car delivers with both performance AND big boy luxury.

    Then I tried this in our 2.0 turbo ’13 Escape. It as well went from an everyday ave of 24.2 to today’s 27.

    Since the Marine fuel has no alcohol, I decided to next try the premium at its ridiculous low cost of 2.19 (today’s price) Premium here is 93.

    Both cars continued their approx 2 MPG increase.
    Now, I am to lazy to do the math, but 2 or more MPG seems like a cool addition for just the .20 cost er gallon and all the extra power and performance, which is what we see around the Ozark area.

    • 0 avatar

      Does the marine fuel still have your state’s standard gas tax tacked on? Around me some stations sell “Off-Road Diesel” that is meant for farm equipment that never touches pavement and if you get caught putting it in a regular truck you are in for a pretty hefty fine

      And I would attribute the additional MPGs to the lack of alcohol (I assume 10% ethanol) you mentioned, not the additional octane

      • 0 avatar

        but the corn in the high octane 93 is still “estimated” around UP to 10 percent. This is percentage of additive not restricted to just the regular or mid…that I am aware of.
        the tank tags do not differentiate from the low,mid or high alcohol percentage.
        Yes…the 91 rated marine fuel is good…but am still concerned about getting caught just in case the hillbillies around here don’t really know the law.
        I am not that aware of the MO restrictions and taxes or fines…if illegal.
        So if I can get the 93 with corn and still get the 2 MPG…for a few cents more (marine and premium about the same price)…great.

        • 0 avatar

          I had a similar kind of issue re: offroad vs highway pumps, only when I used to flog an 82 Rabbit diesel in a mid Atlantic state notorious for its hardcore attitude towards speeding, especially out of staters.

          It shall remain nameless, as I plead the Fifth…

          But I was concerned about fuel gelling in the winter when we would get a real cold spell. In case any of you don’t know, ten to fifteen per cent kerosene does wonders for the problem. However, the ONLY rating for kerosene that must actually meet a standard of purity is kero labelled 1-K. Nothing else means anything objective, not even if it is labelled K-1.

          The problem was that the few stations that sold 1-K kero sold it primarily for use in heaters, hence no road tax, and no highway use stickers on the pump.

          However, nobody seemed to really care, as nobody really felt you should have to be stalled in a diesel car when it was below freezing.

          My neighbor down the block drove a really nice MB 300TD, but was always stalled in his driveway, til he finally came by to ask me how come I was up and running.

          Both of us used 1-K kero for the decade I lived there, with never a problem.

          I never would pull into a station to buy 1-K kero if it was next to a local donut shop, if you get my drift, but otherwise it never became an issue.

          But I also felt like it was best not to go out of my way to test it. I just wanted to be able to go to the store in the middle of an ice storm, to restock on eggs, milk and bread.

          Though as I think about it now, I have to wonder if it was the kero that caused the superfluous screen inside the fuel tank to sludge up and cause intermittent stall problems starting at around 60 or 70K miles.

          If there is a physical chemist among the B&B I’d be curious to hear their opinion. Though it should have been a non-issue, as there should never have been a screen inside the tank, as well as the standard inline fuel filter.

          And I have to wonder now, also, if they weren’t that strict on highway taxes for kero, if they were very strict in testing conformity to the 1-K kero purity standard.

          I used to drive an avgas truck at a local fixed base operator for a summer job while I was in college, and had to drain off a gallon or two every morning. A little caution in pouring it back out of the can I emptied the fuel into yielded a steady supply of avgas for my 59 Plymouth six cylinder.

          No highway tax there either, though the scene was a bit more private than the stations with kero were.

    • 0 avatar

      The reason you are seeing higher fuel economy is not due to the higher octane, but because the alcohol (in normal pump gas) has less energy content per gallon. So alcohol-free fuel has more energy per gallon.

      I have seen the same difference in fuel economy (about 10% improvement) in both my 1990 F350 and my 1997 Civic, using 87-octane regular pump gas and then 87-octane alcohol-free gas from the local farm store (Cenex).

      And trust me on this one – use that alcohol-free gas in all of your outdoor power equipment (both 2-cycle and 4-cycle). Store it in metal containers, and it will still be good a year later. I’ve switched over myself and I leave the gas in all of my equipment over the winter now – starts right up in the spring and I no longer have to take carburetors apart and clean the corrosion out every year or two.

      Check for a station near you.

      • 0 avatar

        yes…I use it in my boat and mowing equipment. I just wanted to try it in the cars as well.

        even with the marine in the boat and equipment…i still use staybil and stuff over winter…

  • avatar

    I recently tried three tanks of Shell 93 (with Ultra Nitrogen infusion!!!) in my stock Charger V8.

    Fuel economy averaged 17.7 on Shell-93 versus 19.3 on Chevron-89 and it seemed less responsive. In fact, I’ll go so far to say it was SIGNIFICANTLY more sluggish on premium. So I went back to 89.

    I’ve never had a positive experience using 93 on a vehicle that wasn’t tuned for it or that didn’t have it recommended from the factory.

  • avatar

    Ive had my FoST since April of 13 and now have 41k on it. This isn’t scientific fact, but rather seat of the pants impressions so take it for what it’s worth.

    1) I don’t buy for a second the stats in C&D about net loss of HP and Torque. The car simply isn’t as peppy when running 87 octane.

    2) With 87 the car bogs down when taking off necessitating a higher RPM launch meaning shorter clutch life. I drive in city traffic primarily so this is a concern for me, you might not care as much. When the AC is running it’s even more noticeable.

    3) Mileage drops a MPG or so, depending on the driving I’m doing.

    4) Doesn’t run as well in cold weather. Don’t get me wrong it runs ok, just not as smoothly as it does with 93 in it.

    5) Even more intriguing is running different brands of 93 octane. I eek out greater overall miles driven per tank on Shell than any other brand. Sunoco is a close second.

    For the price difference in 93 vs 87 (Currently in the Boston area i’m filling up for 2.65/gal for 93, 87 is somewhere around 2.39 last I looked) why NOT go what what’s recommended by the manufacturer? You paid a premium to get the performance of the ST model, why not actually get what you paid for?

  • avatar

    The higher the octane rating (93), the less susceptible fuel is to igniting in the chamber without spark. Conversely, the lower the octane rating (87), the more susceptible fuel is to igniting in the chamber without spark.

    The later can cause fuel to pre-ignite (pre-spark) or detonate (post-spark).

    I’m sure your FiST can detect knock, adjust fuel, adjust VVT, adjust ignition timing as a reactive measure but, personally, I don’t like to see any knock sum count at all. I only run 93 octane and I always recommend those with forced induction to do the same.

    What is the additional cost? $2.00 per fill-up at today’s pump prices?

  • avatar

    For a turbocharged car, 93 octane and the GOOD factory-authorized or aftermarket tune is the best bang for the buck you will ever see.

    2011 GTI: stock 203 hp/215 torque via Dynojet. APR $600 93-octane tune and a good $250 intake: 232 hp/272 torque – same atmospheric conditions, same Dynojet.

  • avatar

    If you plan to drive around the country don’t do a 93 octane tune. You can’t find 93 everywhere. Washington, Oregon and California only go to 91 – some flyover states go to 92.

    • 0 avatar

      I’m the OP (thanks for Sajeev’s and everyone’s comments), and the observation on octane availability is an important one. I live in a fairly rural area and often drive in VERY rural areas. I can usually score 93 for commuting, but there are quite a few towns here in the midwest that only have 87 or maybe 89.

      Before I pull the trigger on a tune from Torrie, I’ll be sure to ask if he’s got an 87 tune available. When I ordered a tuner for my Mustang from Torrie, it came with 89/91/93 tunes. I contacted Torrie and asked for an 87 as well. I had one emailed to me within an hour. That guy is money.

  • avatar

    I have a Lexus ES300, premium recommended but not required. I’ve always used regular and never had any problems or heard any knock. I keep track of the fuel ecomomy of every tank, and because I use the car pretty much exclusively for commuting to work, same route at the same times of day, my fuel economy is very consistent.I buy my fuel at the same gas station, usually from the same pump.

    After one of these internet debates on how premium provides significant improvements in power, smoothness, and fuel economy I figured I’d try it out. The prior 4 tanks prior to switching to premium I averaged 20.7 mpg. The next 4 tanks were premium, and averaged 21.2. I was not able to notice any change in “pep” or smoothness. The next 4 tanks of regular averaged 20.6. Premium cost me about 8% more, and I got about 3% better fuel economy, though I doubt that the increase I saw was statistically significant. A few months later I ran through another 4 tanks of premium and averaged 20.6.

    Then there’s the old E10 debate, and how it causes greater decreases in fuel economy than the 3% predicted by the reduced energy content vs E0. So I tried that too. My usual station doesn’t carry it, so I had to go to another station that carries E0 mid-grade, 89 octane. The next 4 tanks of E0 89 octane averaged 21.2 mpg, and cost 18% more than regular E10.

    May be that premium and ethanol free fuel have greater effects on other peoples cars, but it doesn’t do much for mine, certainly not worth the extra cost.

  • avatar

    Octane is a resistance to knock (what kills engines). By running 93 all the time, you’re just adding an additional safety factor AND getting more power. Stock tune 93 vs stock tune 87 vs Stage 1 93 mapping here:

  • avatar

    All of the people posting here who have naturally-aspirated vehicles with modest compression ratios are missing the point.

    There are a few mainstream NA vehicles in very mild states of tune (because they’re not high-performance vehicles…) that will see somewhat significant improvements from a 93-octane tune, but something like a Civic Si, that is tuned for 91, is not going to see any large gains from tuning for 93.

    Turbo/DI engines will make major gains with higher-octane tunes.

    So no, the 3-liter I6 in your ES300 will not make much more than the 215 hp that it’s rated at, and that engine is a noted gas hog to boot, and that will not improve much with 93.

  • avatar

    I run a Volvo 740 Turbo and even if its rated for Premium, I can put in 87 or 89 without much trouble:

    87: When I need cheap gas, takes away a little mpg and performance but it gets me around.

    89: When I need better gas mileage but still go with cheap gas, probably the best value between the two.

    92-93: When I need to get somewhere in a hurry.

  • avatar

    The 2.0L ecoboost in the Focus ST is rated for 252 hp on 93 octane. You’ll have less power with 87 octane. The 1.6L ecoboost in the Fiesta ST 197 hp rating is also based on 93 octane. The reduction in power for the Focus ST and Fiesta ST using regular vs. premium isn’t listed however if you look at the ratings for the Fusion with the 2.0L ecoboost it says: 240hp using premium and 231hp on regular.

  • avatar

    93 octane isn’t available close to where I live. So I’m only interested in reading about 91 octane tunes, and this is nearly impossible to find (with specific details/charts etc).

    I can understand why not, as most people even considering a tune want to go all out.

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