The Real Impact of Using Wrong Fuel Octane

"Bacon" (bacon117) 08/26/2016 at 22:23 • Filed to: None

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I saw this !!!error: Indecipherable SUB-paragraph formatting!!! on fuel octane on LifeHacker. I work at Ford Motor Company as an Advanced Engine Development Engineer and I’d like to clear some things up, since there is some inaccurate advice on that post,

My views/comments are my own and do not necessarily represent those of my employer (We have these monthly online training sessions, and one of them told me to put this if I identify who I am, so hopefully I don’t get in trouble...)

First Some Background on how Octane is determined:

Octane on the fuel pump is known as Anti Knock Index or AKI, and is the average of a fuels Research Octane Number and Motor Octane Number [(R+M)/2]. The MON and RON are determined by using a special engine with variable compression ratio, and comparing the knocking qualities of a given fuel to that of reference fuels, isooctane and n-heptane. MON and RON have different engine operating conditions, like engine speed, intake temperature, etc. The slope created by these two numbers are important to us engineers in understanding a fuel’s knocking quality in various engine conditions (like boosted, vs non boosted). To the average Joe, the average of these two numbers (what you see on the pump) is what matters.

Next, some background on what knock actually is, and what Octane does to prevent it:

In a spark ignited engine, combustion does not occur instantly at all points in the combustion chamber. Combustion starts at the spark plug and propagates outward roughly spherically. Flame speed is determined by many factors, such as tumble, swirl, piston design, etc. The biggest impact on flame speed is engine speed, so as the engine spins faster, combustion occurs faster. (This is very convenient in terms of designing ignition advance and valve timing)

So, what is knock? Well, as the flame front is propagating across the combustion chamber, the unburnt portion, or end gas, experiences and increase in pressure and temperature. If the increase is high enough, the end gas will spontaneously combust. This spontaneous combustion is very fast and rather violent, so it causes the engine structure to resonate. The resonance is what we hear as knock.

What does Octane do? An increase in octane rating of a fuel represents an increase in the fuel’s auto ignition temperature and pressure. It does not change combustion speed or anything like that. So, if the fuel has a higher auto-ignition pressure and temperature, it takes higher pressure and temperature for knock to occur. The actual mechanics of how this works is complicated chemistry, and this post is long enough already...

Now some background on knock sensors.

A knock sensor is a piezoelectric device. When the piezo crystal inside experiences a force, it generates a voltage. That voltage is then measured by the PCM. The important part of this signal is the frequency of the signal. All engine components create vibration, so the PCM must analyze the signal, looking for specific frequencies associated with engine knock. The PCM performs an FFT (Fast Fourier Transform), or some other proprietary algorithm, to translate the signal from time domain to frequency domain. The results of this FFT are then analyzed to determine if the engine is knocking. If it is determined the engine is knocking, timing is reduced to prevent knocking. This is computationally intensive, so it is difficult to do for transients, like tip-ins, tip-outs, engine shifts, etc. Also, if an engine component creates frequencies near the knocking frequency, it can be difficult to distinguish. So, knock detection is mathematically difficult and computationally intensive, so it can be difficult to do in all circumstances.

So, what happens if you put a higher octane than your car requires?

In short, nothing. Absolutely nothing (except waste money). If the engine calls for 87 octane, then the timing is set for 87 octane. If you put in higher octane, say 93, there is no cause for knock concerns, since it is designed for 87 octane.

What about special additives in premium fuels?

Premium fuel does not have any additional detergents, or anything like that. All fuels must meet strict regulations on detergents, octane levels, sulfur contents, etc. etc. This means, other than octane rating, all fuels are created equal, within a certain standard. This standard is actually very important to engine design, so that we engineers know, within a tolerance, what fuel you will always have in your engine. Now, I say within a tolerance, because fuel formulation can change. One particular example is in colder temperatures. In colder temperatures, the evaporation temperature (Volatility) of the fuel can be lowered, allowing for the use of less expensive additives to meet the octane requirements. This is why you may notice a change in fuel economy when comparing summer to winter.

What happens if you put a lower octane than your car requires?

In short, MAYBE nothing. This one is kind of a big risk. The stack exchange article says that a modern knock sensor will correct for lower octane fuel. This is true, but only in steady state conditions; like cruising down the road, or steady uphill, etc. Transient conditions are where the problems lie. Since it does take time to analyze the knock sensor signal, fast changes in engine load or speed, are difficult to prevent knock. Every automaker is going to be different in this regard, since the ability to analyze this knock quickly depends on the skill of the programmers and calibrators and even the speed of the PCM processor. So, if you put in a lower octane fuel, and then go drive your car hard, press the accelerator quickly, it is possible to experience heavy knock, and possible engine damage. I will say, it is unlikely to actually happen in cars produced in the last few years, but you are certainly exposing your engine to the possibility. ALWAYS, ALWAYS, ALWAYS use the fuel recommended in the owners manual of your car, or any signs on the fuel door or cap. When engineers say to use a certain fuel, we have good reasons for doing so.

TL:DR

Always follow what your manual recommends. If your engine calls for 93 octane, USE 93 octane. Don’t risk engine damage.

RedlineZ bought an SV (And is getting rid of the z) > Bacon 08/27/2016 at 00:24

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i just finished reading that and it seemed like it was written by someone who did a quick google and posted what they found. probably should have left it to Oppo/Jalopnik and re-posted it over there. way to go in depth here though.

ITA97, now with more Jag @ opposite-lock.com > Bacon 08/27/2016 at 00:27

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Is there a relationship with octane and altitude? I ask because in the mountain west we usually have 86, 88 and 91 available. In places in colorado, I see 85 being sold to this day, and I don’t think I’ve ever seen 93 sold in New Mexico, Arizona or West Texas. 100 and 110 unleaded race fuel is sold by one place Albuquerque and by the barrel from a speed shop in Las Cruces . I’ve never owned a car that required 93. Would I be boned living in New Mexico?

Zachary Oberle > ITA97, now with more Jag @ opposite-lock.com 08/27/2016 at 00:31

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I just drove to Palisade, Colorado yesterday and was positively gob-smacked by the presence of 85 octane at a local fuel station. I had no idea anybody still sold such a thing!

ITA97, now with more Jag @ opposite-lock.com > Zachary Oberle 08/27/2016 at 00:35

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I felt the same way the first time I saw 93 octane in the Midwest. I had no idea such a thing was sold at a regular gas station.

Bacon > ITA97, now with more Jag @ opposite-lock.com 08/27/2016 at 00:36

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All of the work I do is at 100kPa pressure (roughly sea level), so I don’t have specific experience with Octane and altitude. It may have to do with the fact that fuel will evaporate at a lower temperature with lower atmospheric pressure (just like water boils at a lower temperature), but I’m not really sure. You might be able to find more information on the internet somewhere, but I would take it with a grain of salt. Sorry that I can’t specifically answer your question.

Zachary Oberle > ITA97, now with more Jag @ opposite-lock.com 08/27/2016 at 00:39

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Oh, we’ve got plenty more than that here in the corn belt!

Bacon > RedlineZ bought an SV (And is getting rid of the z) 08/27/2016 at 00:42

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When it comes to engines/fuels/oil, there is SO much information, and when you get into engineering an engine, there are SO many variables and effects. The internal combustion engine is SERIOUSLY complicated when you start getting into the thermodynamics, chemistry, and mechanics.

The problem is that most information I have ever read is not ENTIRELY wrong. Also, some if it may have been true historically. For example, maybe 50 years ago, before fuel was as highly regulated as it is today, premium fuel really did have better quality components.

Anyway, I’m glad you liked my article but, even this is just scratching the surface.

ITA97, now with more Jag @ opposite-lock.com > Bacon 08/27/2016 at 00:53

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That could make sense. Thinking about it, I do know that compression testing an engine up here will yield lower results in absolute value, given everything else being equal. I could see the hypothesis that slightly lower compression equals a slightly lower octane requirement, so they save some pennies at the refinery/ wholesale distributor or where ever it is that they’re adding additives in the process. At my house, water boils about 204 degrees.

DipodomysDeserti > Bacon 08/27/2016 at 01:36

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Do you have any info on how different additives affect the octane rating of gasoline. For example, it's well known within the tuning community that not all 91 is created equal. 91 octane in CA, AZ, and NV is more prone to knock than other states (we have different standards that has has to meet). It's such a common issue that Cobb has specific tunes for cars located in these states.

Xyl0c41n3 > Bacon 08/27/2016 at 02:00

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TIL.

Thank you! This was a great read.

John Doe > Bacon 08/27/2016 at 03:03

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Fuels definitely can have varying and different amounts of additives. Doesn’t mean it’s better, but there are differences.

!!! UNKNOWN CONTENT TYPE !!!

Shell V-Power NiTRO+ contains the highest concentration of the Shell Nitrogen Enriched Cleaning System and cleans up faster than Shell regular. In fact, Shell V-Power now contains seven times the amount of cleaning agents required by federal standards . The new Shell V-Power NiTRO+ formulation contains an innovative combination of two key cleaning agents that work together in harmony to provide the BEST TOTAL engine protection you can get. It provides unbeatable protection against gunk and corrosion, and superior protection against wear.

RedlineZ bought an SV (And is getting rid of the z) > Zachary Oberle 08/27/2016 at 03:06

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$5.50 a gallon? what the actual fuck is that about. that is absolutely insane i just filled up in NJ with 93 for $2.45/gal

Jonathan > RedlineZ bought an SV (And is getting rid of the z) 08/27/2016 at 04:33

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Looks like an old pic if 87 is $3.84. Look at the octane ratings. The reason it is so expensive is that those on the left are racing fuels. They are likely leaded. It is more expensive to process fuel to this octane rating and does not enjoy the same distribution infrastructure as other fuel.

YumYumOfTheYum > Bacon 08/27/2016 at 05:08

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And.. Some people may call me too old fashioned, but herein lies one of the beauty of the rose tinted days of old.

I'm not an engineer, but my dad is somewhat a car enthusiast. We had a lot of wrenching time together, and I learned a lot about car maintenance and driving discipline, manners and all, but especially the feel.

To put it bluntly, it is impossible for a good driver to not feel a knocking engine, no matter how tiny it is and no matter how expensive and smooth running the engine is.

So.. Protip (to help with the argument that feeding your engine lower octane than rated may or may not do something bad to your engine) :

Feel the engine. When you know it’s knocking (assuming the engine is tuned properly), buy higher octane.

Problem solved. (bear in mind that even *assuming* the engine is invulnerable to knocking, it is a fact that knocking DOES destroy engine mountings in the long run)

But then again, the millenials’ solution is always electronic nannies..

Needmoargarage > Bacon 08/27/2016 at 07:35

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Hello fellow Ford engineer! Are you in GEE?

I feel like I have to explain this concept to people constantly...going to favorite your post and direct them here.

I ask therefore I am > Bacon 08/27/2016 at 07:37

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Will using a higher octane fuel on a modified car make a difference? Let’s say the air filter has been replaced to allow more air or the engine has been port and polished.

My X-type is too a real Jaguar > Bacon 08/27/2016 at 08:30

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Ive tried to convince my father of this since the 1990s when he bought a Turbo Eclipse, called for premium and he ran mid grade, then he got a 99 BMW 328 he ran it on regular because “it has a knock sensor I’ll be fine”.now he has a 14 335 it calls for 90 octane he runs mid grade because “89 an average should be close enough” He's a retired chemist and thinks engineers are too cautious.

LongbowMkII > Bacon 08/27/2016 at 09:43

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Does ambient air temperature (therefore intake temperature) have an appreciable effect on knock? I usually go 89 for my 87 recommended engines when it’s going to be 95-100. I realize it’s probably pointless, but the extra $2-4 a summer makes me feel better.

Or are modern cars designed so they don’t need to pull timing to run 87 up to 150' or whatever.

Perhaps it’s a carry over old mechanic’s tale from the old days with no electronic knock sensors.

fhrblig > ITA97, now with more Jag @ opposite-lock.com 08/27/2016 at 09:57

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I’m in Colorado and I’ve always used the one that’s two points lower than the recommended and had no problems. We don’t even have 93 in most places; the highest octane we have is 91. I used 91 in my Fiat that recommended 93 and had no issues. I have a fleet of vans and trucks at work that all call for regular and have had no problems using 85.

I have used E-85 in a couple of the full size V8 vans when we first got them, but the mileage drops from 14-15 mpg to 11-12. You notice a power increase though. E-85 smells like if Kellogg’s Corn Pops made an alcoholic beverage.

jdrgoat - Ponticrack? > Bacon 08/27/2016 at 10:47

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I agree with your article, and this is also in line with the advice that I give people if they ask, too. But recently I have found an inconsistency when it comes to not using a higher octane than the vehicle calls for.

My truck has a 2.5L 4cyl, runs 11.3:1 static compression, and is rated at 200hp @ 6300rpm. Yes, it’s basically a car engine. But, and I think this is important, I also have a manual so there’s less masking or absorbing of engine vibrations that a torque converter would have.

While running steady state, or very, very slow constant acceleration, I would feel a sensation that the engine was hesitating. It would pull normally, then a hiccup, then normal, then a hiccup. It felt to me like timing was being pulled, or maybe the VVT was doing something tricky. I noticed this pretty much every day on my commute on a stretch of residential road, and I drive gently. Under 2000rpm, very light throttle. Sometimes accelerating in 5th from 35-45mph.

I went old school in my thinking, and figured that a 11.3:1 SCR was ridiculous to run with 87 octane. As soon as I switched to 89 and gave the computer some time to learn, that feeling of hesitation that felt like timing being pulled went away. It drives much smoother, and the fuel economy has even been better.

I have 91 in it right now because it was $0.04/gal more than 89 was, but I’m sure the octane is just from more ethanol. I’m curious if the economy will go down on this tank.

Anyway, I guess my point is, it seems that some modern cars might actually benefit from a bump in octane. I wouldn’t be surprised if the engine is built to “accept” 87, but run more advance with 89 providing smoother operation and better economy. I haven’t done any data logging myself, but I saw a friend post some of his logs comparing regular to premium, and the peak power stayed the same, but everywhere under the curve was improved with more octane.

Wow that got long for an anecdotal story.

area man > Bacon 08/27/2016 at 11:00

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This is one of the smarter articles ever posted to Oppo. Great job man, I learned a lot.

Zachary Oberle > RedlineZ bought an SV (And is getting rid of the z) 08/27/2016 at 11:04

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Yea, Jonathan’s got it. Old pic and race fuel has narrow distribution, makes it expensive.

The *real* race gas of the Midwest is E85. You can find it everywhere here and it consistently delivers more than 100 octane.

TheVancen- In Pursuit of a Greater Payday and Car Parts > Bacon 08/27/2016 at 12:06

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What do you think of octane boosters? I’m talking about the bottled stuff, not the old school mothball trick.

Say I have an engine that requires 100+ octane race fuel, and I simply cannot find it where I live, premium pump gas and bottle of the booster should be enough right? Last time the engine ran, it had been using an STP octane booster with Canadian 93 octane.

Do you know the chemistry of why mothballs wake up old gas? When I went to get the engine running in my Taurus before I bought it, the fuel smelled like varsol, so I dropped one in the tank and it was enough to get the car to run and drive it up on the trailer. (After crashing into the garage door but that’s another story.)

Bacon > Needmoargarage 08/27/2016 at 12:14

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Hello to you too! Used to be in component C, but i’m over in RIC now.

Bacon > TheVancen- In Pursuit of a Greater Payday and Car Parts 08/27/2016 at 12:19

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I don’t know much about the chemistry of octane boosters, and what they are made of. Do you know what the actual octane rating is after adding the bottle? I think it would be hard to be absolutely certain. I suppose if the race engine isn’t knocking, you have a high enough octane. That is a bit risky, in my opinion. If I were you, I would purchase a drum of race fuel, or find someone close to you who will sell you some of theirs.

Needmoargarage > Bacon 08/27/2016 at 12:26

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Very cool! FCG here...currently on rotation with FP Motorsports but looking for a permanent home in GEE soon.

fritzo > Bacon 08/27/2016 at 12:30

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I’m a Mini Cooper S driver, and while you’re supposed to use 91+ octane, the manual states 87 can be used occasionally. However the dealsship says low octane fuel causes carbon buildup and eventual loss of power. This results in needing the engine torn down and “acorn she’ll blasted”.

Bacon > jdrgoat - Ponticrack? 08/27/2016 at 12:31

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11.3:1 is a fairly high compression ratio. Is it stock?

Some modern cars will advance timing to take advantage of higher octane ratings, that is true. It’s difficult to tell which cars will and will not do it, which is really back to my main point, read the owners manual. That SHOULD tell you if running higher octane will provide benefits.

Bacon > fritzo 08/27/2016 at 12:38

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I’m not an expert on Mini Coopers, but I’ll give you my best guess: Allowing 87 octane only occasionally is a way to reduce the likelihood of experiencing knock. If you use it all the time, your much more likely to experience knock.

Octane rating will not affect carbon buildup. I suspect the dealer is using that as a way to get you to use the 91 octane. So their hearts are in the right spot...

Does this engine use Direct Injection?

Bacon > LongbowMkII 08/27/2016 at 12:48

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Absolutely. Intake air temperature has a very big effect on knock. Remember, fuel will spontaneously combust if it reaches a certain temperature and pressure line, so if that starting point temperature is higher, it will absolutely knock sooner.

Is it a waste to use higher octane in this case? It’s really hard to say. The best way to tell is to get a data logger, and see if timing is being pulled with 87 octane.

If timing is being pulled is it actually a value to use higher octane? This is even harder to say. You would have to know how fuel economy is affected by a few degrees of combustion phasing (ignition timing), which requires highly accurate fuel flow and torque measurement.

But, if it’s only $2-4 for the whole summer, why not?

NYankee1927 > Bacon 08/27/2016 at 13:05

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Can you comment on turbo engines? Specifically, certainly not an eco-boost and definitely not an F150. Will modern engines take advantage of the higher octane and give more boost? I guess the real question is do any turbo engines run a closed loop control varying the boost with the feedback of the anti-knock sensor?

fritzo > Bacon 08/27/2016 at 14:32

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Yes it does. There may be something up with the design too (It’s the ‘Prince’ 1.6L turbo engine made by Peugeot). Carbon buildup is well known in these engines, with the only way to cut it down seems to be to drive it like you stole it :D. That engine is happiest around 4K RPM, but a lot of people that drive Coopers drive them at low RPM to keep the engine noise down.

Here’s an example of the shell cleaning:

atfsgeoff > Bacon 08/27/2016 at 15:14

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What about vehicles like a later model Mustang GT, which has two different HP ratings depending on the octane you use (412 vs 402)? Is it safe to use 87 octane routinely in say, a 2013 Mustang GT, if you’re not concerned about losing 10hp?

jdrgoat - Ponticrack? > Bacon 08/27/2016 at 17:59

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Bone stock. It’s a GM LCV in a Colorado. Every review of a vehicle with this engine is guaranteed to call it a dog. But in my experience, I’ve been very surprised and impressed by it. We’re in a freaking golden age when I can have a 200hp 4cyl in a truck that weighs 2 tons and gets better than 25mpg. I figured out how to launch it once, too, and spinning the tires at 4000rpm for a couple seconds before gaining traction was pretty fun. Even if 0-60 happened in 9 seconds.

I should actually read the manual, I suppose. Hold on a sec, it’s just in the other room.

...intermission...

Yep, the only mention of octane is to not use lower than 87 octane “as it may cause engine damage and will lower fuel economy.”

I should see if Torque can log enough to validate my claims on improved smoothness. The thing is, I don’t want to put up with 87 for that long. :P

Bacon > fritzo 08/27/2016 at 18:07

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Unfortunately, all DI engines are prone to carbon/oil buildup on the intake valves. Since there is no fuel flowing past the intake valve, any oil particles that make it through the PCV system will build up on the back of the intake valve. I would expect a PCV system catch can to help, but I have no experience with these on mini coopers. Again since there is no fuel flowing past the valves, no type of fuel will help.

gizmo-ms3 > Bacon 08/27/2016 at 19:01

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I have a ‘15 Focus ST. As I’m sure you know, the owners manual says you can use 87 octane, but make 8 less horsepower. Any other negative to using 87? I’ve tried both and didn’t notice a difference, but people on forums are like ZOMG DON’T USE 87 OR YOU’LL BLOW YOUR MOTOR.

Manwich - now Keto-Friendly > Bacon 08/27/2016 at 19:19

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I was about to mention something about this... And how on some cars I’ve had, in hot weather, I can hear a bit of knock that isn’t there if going up to 89 octane OR isn’t there in cooler weather.

Manwich - now Keto-Friendly > Bacon 08/27/2016 at 19:22

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Could the use of synthetic oil with a higher vaporization and flashpoint temp be used to reduce carbon buildup? In theory, I think it could help.

Bacon > Manwich - now Keto-Friendly 08/27/2016 at 19:58

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That is certainly out of my wheelhouse. I don’t know much about oil beyond what you can read on the internet, and that viscosity has a measurable impact on fuel economy. I do have a training class in October where I hope to learn some of this from the real oil experts.

Bacon > gizmo-ms3 08/27/2016 at 20:23

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If you go from using 93 to 87, and go WOT, you might notice some light knocking before the PCM adjusts. Some knock HAS to occur before the PCM knows there is lower octane rated fuel in the tank. There is no way to measure octane rating directly. This light knocking isn’t going to hurt anything, but might scare you. If it continues for more than 10 seconds or so, it’s abnormal.

This is what I mean about reading the manual. If the manual says you can run either fuel, then some light knocking might occur when you go from a high octane rating to a low octane rating. But, if the owners manual says only 93, and you run 87, you’re going to have a bad time.

davesaddiction @ opposite-lock.com > Needmoargarage 08/27/2016 at 21:18

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I have no idea what you’re talking about, but... INDUSTRY ACRONYMS!!! So fancy. =)

irisfailsafe5000 > Bacon 08/27/2016 at 21:26

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Where I live Mercedes Benz demands Premium fuel and their biggest engine problems occur when people use regular gas and I don’t know why but it messes up the engine and since they told you tu use Premium the fixing is not covered by warranty.

Needmoargarage > davesaddiction @ opposite-lock.com 08/27/2016 at 23:55

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Haha...I know. It’s a language within itself. Here at Ford we even have a site to look look up all the ridiculous acronyms we use!

davesaddiction @ opposite-lock.com > Needmoargarage 08/28/2016 at 00:35

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Think of all the time that saves!

gizmo-ms3 > Bacon 08/28/2016 at 01:08

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Great, thanks!

jimz > gizmo-ms3 08/28/2016 at 10:27

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turbo engines have a bit more flexibility as they can also reduce boost.

In a Mini; let them mock me as My Mini Countryman is higher than you > Bacon 08/28/2016 at 15:54

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UNRELATED SOMEWHAT.

Where did you go to school?

Hardest Class

Should I dual Major

Can I have fi\un while studying to be an engineer?

Why am I asking these questions to you? I’m a 1st year AE/EE hopeful. PLS help.

Bacon > In a Mini; let them mock me as My Mini Countryman is higher than you 08/28/2016 at 16:20

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Went to Lawrence Tech University in Southfield, MI. (Am still going for my Masters)

Calc and Diff EQ. Although now that I’m doing my Masters, and am actually paying attention, it isn’t that hard.

Dual is not a bad idea, especially if you are doing EE. I did ME, should have done ME/computer or something along those lines. I suspect dual matters less than a masters, but I have not gotten my masters YET, so I’ll let you know in a few years.

Haha. Maybe. If you are full time and trying to be an A student, probably not. I joined a fraternity, was probably the best and worst decision at the same time.

There is a difference between education and certification. If you are just looking for the certification, grades don’t matter as much. BUT, you WILL have less opportunities when you graduate. 5-10 years into your career, school grades will have less of an impact, but those first few years can really impact your career path. I took the certification approach, and have had to work my ASS off to get anywhere. It’s not impossible, but I highly recommend busting your ass in school.

The education route is where you go to class to actually learn the thing not just get the grade, and truly understand it. This is where you will probably have to be anti-social, unless you are a genius and can memorize everything. Usually learning the thing brings about the A grades.

Whatever you do, don’t give up, and really pay attention to the cost. LTU is a private school, and as such is a TON more money. Probably double had I gone to a public school. LTU is a good school, but you certainly pay for it.

In a Mini; let them mock me as My Mini Countryman is higher than you > Bacon 08/28/2016 at 16:24

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I’m at UF. YOU LIVED IN MICHIGAN AND DIDNT GO TO UM ANN ARBOR??

I’m just jealous that some people get instate for UM Ann Arbor:(

DailyTurismo > Bacon 08/29/2016 at 01:32

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Bacon,

Quick question — would you have any interest on being a guest on the Daily Turismo Radio show and talking to us about Octane and engine development? Let me know via e-mail vince@dailyturismo.com. As a fellow mechanical engineer and engine geek (actually, all three of us who regularly host the show are MEs), I think we’d have lots to talk about.

Let me know! -Vince

Just Another Gawkfugee > Needmoargarage 08/29/2016 at 07:04

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Same with my company.

Our db of Three Letter Acronyms is called, of course, the TLADB.

And TLADB is the first entry in the FLADB. :-)

StndIbnz, Drives a MSRT8 > Bacon 08/29/2016 at 08:59

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Thank you! As a fellow automotive engineer working in powertrain, I hate seeing articles like this where you know the writer doesn’t know a lick of what they are talking about. They got close, but for the love of god please use the fuel we designed the engine for. It was calibrated to run with that, so don’t complain when your engine makes less power and gets worse MPG’s because you put in 87 instead of 91-93.......

StndIbnz, Drives a MSRT8 > Bacon 08/29/2016 at 09:01

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LTU, fraternity and works at Ford. Your frat didn’t happen to have a crazy kid with a Conquest in it did it? Only frat I know of at LTU (went to OU) and I’m currently working with him.

functionoverfashion > Bacon 08/29/2016 at 09:52

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I also take real issue with this statement, quoted from the StackExchange article:

E10 fuel poses no issues for modern or older vehicles

This is absolutely false. When E10 was introduced into my area, it caused - and still DOES cause - countless issues, in particular with old vehicles, small engines that are used infrequently, and of course, boats.

The tendency of ethanol-blended fuels to attract water, and eventually phase-separate, causing water to be sucked into the fuel system, causes issues with boats to this day, far more often than non-ethanol fuels. Working at a marina, we had to quadruple our storage capacity for water-contaminated fuel after the introduction of E10.

It also wreaks havoc on small engines that sit for weeks at a time between use - it has made fuel stabilizer an absolute necessity in all small engines, at least in my experience. This wasn’t necessary prior to E10.

My own boat is a 1989, which is not all that old, really. I had owned it for 3-4 years when ethanol fuel came around. It’s a well-used inboard, with a bulletproof 351 ford block and a 37-gallon aluminum tank. I put in about 20 gallons of E10 (with maybe 10-15 gallons of other fuel in already) and started it up. It ran for about 5 minutes and died, then wouldn’t re-start. This, after it had literally NEVER had so much as a misfire in the time I’d owned it. The E10 cleaned out all the old deposits of whatever in my fuel tank, and clogged the fuel pickup and the first fuel filter - I have two filters. It’s been fine since, but it was a direct cause-and-effect that we saw play out with hundreds of boats.

Even worse? Fiberglass fuel tanks. The ethanol would dissolve the lining of the tank and pass the solution on through the fuel system, clogging everything with a nice varnish along the way. The solution? Tear up the floor and replace the tank, then go through the entire fuel system, all at great expense.

I’ve seen it eat gaskets on older carbs, collapse fuel lines, gum up carburetors after only 60 days of dormancy, and more. To say that “...E10 fuel poses no issues...” is only true in the sense that an engine will run fine on the fuel, technically speaking.

Note: I am aware that some of the early issues were caused by imprecise mixing - causing fuel labeled E10 to be more like -15 or -20, or worse. But still, you can tell from my long rant how I feel about someone touting the wonders of E10 - or even saying it’s harmless. It’s not.

functionoverfashion > Bacon 08/29/2016 at 09:55

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Your post here got linked in the LifeHacker article. I guess you’re famous now, or something? Well done.

Bacon > StndIbnz, Drives a MSRT8 08/29/2016 at 09:55

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I was in Theta Tau, and that Sounds like Dave. lol He will know who Bacon is.

Bacon > functionoverfashion 08/29/2016 at 09:56

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Well, I DID email the author of that article. :)

StndIbnz, Drives a MSRT8 > Bacon 08/29/2016 at 10:01

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Ha yup.

Nice write up BTW.

Elkidmino > Bacon 08/29/2016 at 10:12

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Dave here. Good post Bacon, nice to see real knowledge being shared on the Interwebz. I'd like to share more on turbos but fear the wrath of our overlords.

Bacon > Elkidmino 08/29/2016 at 10:16

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I’m not sharing anything proprietary, and I added the blurb about these being my thoughts, not Ford’s. Hopefully that appeases the gods.

MontegoMan562 is a Capri RS Owner > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 10:19

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I understand that education wise, UM Ann Arbor is a great place to be. A large portion of people going to school don’t like that atmosphere though (built into the city of Ann Arbor) Me personally, I was coming from out of state (so I had zero built in MSU vs UM bias) and preferred the Michigan State campus/environment and the program I was looking at had a difference in national ranking of 6. Yeah, just 6. It was #9 vs #15. When it comes down to that, you pick the place you want to be because both programs are fantastic.

I ended up switching majors to one that UM didn’t even have and it was a top 5 nationally ranked program at MSU so that worked out.

Basically, just like the Miata - UofM is not always the answer.

Rico > Bacon 08/29/2016 at 10:21

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But but but by using 87 instead of the required 93 I save a total of $3.50 on my fill up! /s

yamahog > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 10:33

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Graduated with a BSE in Aero from University of Michigan. Out of state tuition. AMA...

In a Mini; let them mock me as My Mini Countryman is higher than you > yamahog 08/29/2016 at 10:49

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CAN I BE YOU???!!!!!

Same questions I asked Bacon.

In a Mini; let them mock me as My Mini Countryman is higher than you > MontegoMan562 is a Capri RS Owner 08/29/2016 at 10:50

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Im at UF, GO GATORS!!!!

yamahog > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 11:12

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My hardest class was probably one of the two engineering classes I took a W in... One MechE class, one aero. I can’t remember the exact topics at the moment. Fwiw I found DiffEQ to be one of my easier classes.

If you want to dual major, just be aware you probably won’t graduate in 4 years and adjust your financial expectations accordingly.

I had tons of fun, but that was because I won a scholarship/internship deal with Northrop Grumman straight out of high school so there was a bit less pressure on my grades than most people. Speaking of - DO NOT SCREW YOUR FIRST YEAR GPA. Those are likely your easiest courses and will greatly help your overall GPA as classes get harder later on. By all means, make friends and have fun, but eyes on the prize. I had a job, rushed and joined a sorority, went out every Thursday/Friday/football Saturday, had a really rude awakening from how easy high school was, realized 8am Friday Calc III was not a good choice, and my freshman grades weren’t the best. If I hadn’t already had that internship lined up, my resume at that point wouldn’t have been very competitive at all.

Snuze: Needs another Swede > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 11:51

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BSE in Mechanical from UMD. I’ll second what Bacon and Yamahog have to say - bust your butt freshman year and work hard - it’s going to be a huge shock after high school and feel super hard, but the reality is it’s your easiest year. So get the best GPA you can as early as you can. That way if you get a bad grade later it won’t sting so much. It’s easier to spend your remaining 3 years riding your GPA down as gently as possible vs. trying to claw your way back up from a terrible freshman GPA.

Also, dual majoring can be amazing, and hard. I have a friend who dual majored in ME and Aero, took him 6 years to graduate. But how he works for Redbull F1. So yeah, it can get you places but you gotta put in work.

On the flip side, it took me 10 years to get a degree (see above about working hard freshman year). I went to school for 3 semesters as an EE, bombed hard (1.9 GPA), dropped out, did a 6 year hitch in the Navy, and then went back for my ME. The Navy discipline made school so much easier the second time, and my service helped my career a ton, because otherwise I wouldn’t be where I’m at.

Last bit of advice, which has already been tossed around - do stuff in school! Don’t be the guy who only goes to class, does the bare minimum, and then sits in the dorm and eats pizza and plays video games. I was never in a frat, but I can tell you it’s a good deal because you will run into frat brothers later and you all look out for each other. My current boss was in a frat and I can tell you when we’re hiring brothers from that frat get their resumes at or near the top of the pile. We vet’s do the same, the old boss here was a former Marine, and he wanted another mil guy in the department. Also join a technical society, like ASME, and/or do a fun project like Formula SAE. I have another friend who was the bare-minimum guy like I described above and 3 years after we graduated he’s still significantly under-employed (doing logistics for a cargo transfer company). When I was about to graduate I “got” a job just based on my involvement in FSAE. The interviewer had done it at PSU and we spent 90% of the interview talking about how much fun Formula was. I was hired but then they lost funding so no job, then I interviewed with the ex-Marine as I mentioned above and landed at my current gig. Also, do summer internships. Just like doing a frat, society, Formula, whatever, it helps you stand out, and gives you valuable experience and if nothing else maybe teaches you where you don’t want to work.

MikaelVroom > Bacon 08/29/2016 at 12:02

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An increase in octane rating of a fuel represents an increase in the fuels auto ignition temperature and pressure. It does not change combustion speed or anything like that.

Thank you! I’ve had so many internet arguments with people (even other engineers) claiming that higher octane fuels “burn slower.” Strangely enough, no one has ever been able to source that claim.

Here’s a question about cars like the Mustang GT that produce their rated power on 91+ octane but state are safe to run on 87. You’ve mentioned that the computer will pull timing after a while when you’ve switched from 91 to 87. But does it then periodically advance the timing to see if it can go higher? With what frequency does that happen? Does it check once per drive, or once per week, or each time you hit the accelerator? I’m just curious about how long it takes for the computer to ramp back up once you’ve put higher octane fuel back in.

Thanks for the article, it was great!

ateamfan42 > Bacon 08/29/2016 at 12:24

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Thank you for an informative article. Stamping out the widespread ignorance that surrounds fuel octane is a tough challenge! It doesn’t help that marketing calls high octane gasoline “premium”, suggesting is somehow overall better for cars.

Premium fuel does not have any additional detergents, or anything like that.

This myth may never be stamped out. There are lots of people who are convinced that premium = more detergents, or more refined, or some other nonsense.

Always follow what your manual recommends. If your engine calls for 93 octane, USE 93 octane. Don’t risk engine damage.

Sadly, this rule cannot always be followed. Thanks to regulation changes in 2009 with the EPA mandate to E10 fuel, the “premium” fuel selection in many places changed as well. Many folks now cannot purchase the fuel their car was designed to use.

In a Mini; let them mock me as My Mini Countryman is higher than you > Snuze: Needs another Swede 08/29/2016 at 12:29

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I’m going to do Drama at my school.

YEAH. And FSAE if I can ever make my way over (it's on the opposite side of campus from where I live and take classes

Snuze: Needs another Swede > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 12:31

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Its worth the walk. I learned so much in that program, and made some really good friends.

In a Mini; let them mock me as My Mini Countryman is higher than you > yamahog 08/29/2016 at 12:31

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>Northrop Grumman job

AHHHHHHHH. Holy god damn fuck that’s my dream!!! My life has been planes, trains, and automobiles! Mostly planes.

How did you deal with sucky roommates?

ateamfan42 > TheVancen- In Pursuit of a Greater Payday and Car Parts 08/29/2016 at 12:32

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Make sure you read the fine print on those octane boosters to understand what levels they are claiming to achieve. Most will rate in “points”, which don’t mean what many people think they mean.

When a bottle of booster says “raises octane 8 points”, it doesn’t meant it will convert your tank of 91 PON to 99 PON. It means it claims to boost your tank of 91.0 PON to 91.8 PON. Not nearly as dramatic as you would hope.

Those boosters might be helpful if an engine is just BARELY starting to knock, and you need just a tiny bit more detonation resistance. They aren’t going to turn regular pump gas into full-out race gas.

In a Mini; let them mock me as My Mini Countryman is higher than you > Snuze: Needs another Swede 08/29/2016 at 12:32

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Good point.

yamahog > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 12:37

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Eh, it *was* my dream gig too, but I left after a year full-time on the F35 program for multiple reasons and I work in the auto industry now.

As far as roommates... I didn’t really have any issues. Freshman year girl came in with tons of high school friends so they always hung out, I did my own thing with sorority and engineering friends. Sophomore year I lived in the mansion, junior and senior year I lived in apartments/houses with friends. Most years I had an SO to stay with too.

MontegoMan562 is a Capri RS Owner > yamahog 08/29/2016 at 12:41

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I may not be in engineering but this is the best advice for all college students.

In a Mini; let them mock me as My Mini Countryman is higher than you > yamahog 08/29/2016 at 12:46

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*Tongue drops on floor*

WEW.

Thanks 4 your help. I messed up on my AP Calc exam and math placement test for college. I’m in Precalc and wondering if I should give up on my dream and become a SEC Lawyer. I know, two completely different things.

In regards to social things. I have clusters of friends. But theyre in different majors or ahead of me in Math

yamahog > MontegoMan562 is a Capri RS Owner 08/29/2016 at 12:51

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Thanks :) I really went overboard with the stereotypical “high school overachiever with shitty home life goes wild when given freedom” thing at first, but luckily I got my shit together enough to graduate in four years with multiple job offers.

yamahog > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 13:20

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Honestly, starting a bit lower in math isn’t the worst IMO. Essentially retaking a course with material you already know (to some extent) will make for a smoother transition to university level coursework and hopefully help you start on the right foot with good grades.

My fiancé would not recommend law school, for what it’s worth. Too many young lawyers and not enough jobs is making competition extremely fierce, not to mention taking on more loan debt for law school.

BLCKSTRM > Bacon 08/29/2016 at 14:28

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Nice!

I’ve thought about doing something similar with this article:

http://twocents.lifehacker.com/the-car-brands…

The important part is this:

In order to estimate annual maintenance costs, we found the amount spent on every two oil changes (as oil changes are generally done every six months).

Which is a problem since the very next sentence says BMW’s are the most expensive. You know, those BMW’s that people complain about since they take 8 quarts of synthetic? Apparently the author has no clue about oil composition or capacity since BMW’s (and other luxury cars, I assume) also take a huge quantity of synthetic and give you an oil change interval of 15,000 miles - or at least a year for most people.

In any case, your article and this one I’m referencing are examples of what happens when non-Jalopnik writers write car articles.

MontegoMan562 is a Capri RS Owner > yamahog 08/29/2016 at 14:34

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I got it done in 4 as well after a shit freshman year that consisted mainly of video games and alcohol. It was a hell of an awakening giving I coasted through high school on honor roll while barely opening a book. Thinking I could do the same thing in college was a huge mistake, unfortunately no matter how much I was told that going into it - it’s something I had to learn for myself.

Bacon > MikaelVroom 08/29/2016 at 17:11

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Here is one for you: If you decrease octane rating, and the engine is operating where you must retard spark, retarding spark will actually slow combustion a very small, but measurable, amount. So, in effect lower octane slows combustion! Not directly, of course, but the ICE is so complicated that there are no rules of thumb when you get down to the details.

There are, however, ways to actually slow down combustion. Exhaust Gas Recirculation (EGR) is one way. EGR acts as a diluent in the chamber since EGR is inert. This means it actually impedes combustion. Perhaps that’s where the confusion comes from, because EGR is most certainly used to reduce the propensity for knock by slowing down combustion. This is a different mechanism for reducing knock than increasing the octane number, however.

Any information I share on here is publically available. Head on over to SAE.org and have a look. Most full papers cost money, and they can be difficult to read even for seasoned engineers.

Unfortunately, since I am a Ford Engineer, the answers to you Mustang question are too close to sharing non-public information for my comfort. There are OBD tools you can purchase that might let you answer your own question. :)

MikaelVroom > Bacon 08/29/2016 at 17:57

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Thanks for the response!

smobgirl > In a Mini; let them mock me as My Mini Countryman is higher than you 08/29/2016 at 20:39

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Late to the party. I started college as an AE Major at UVa. Dropped the major because of partial diffEQ/Vector Calc. Can’t guarantee that the subject was really that bad but the professor was only fluent in Russian.

My suggestion? If you end up in that sort of situation (required class, only one possible professor, nothing makes any sense) - find support. Find a solution. Don’t just drop the entire idea of engineering because no one knows what to do next.

Wolfpack86 > yamahog 08/30/2016 at 11:40

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Yeah, Calc II freaking sucked. Made Diff Eq seem like a cakewalk IMO.

thebigbossyboss > Bacon 08/30/2016 at 12:54

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Thank you for this. I shall only put in 91 in my Mustang GT hence forth. I usually do put it in, but if fuel prices are eye wateringly high, sometimes I put in 87. I’ll stop. I plan on having this car for a long time and $4-5 at the pump isn’t worth the damage.

Although to be fair, I did check my owners manual and it said “using 87 will not damage your engine” which is a dick thing to say if it does in fact lead to a damaged engine.

Scott > MikaelVroom 08/30/2016 at 12:57

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I’m not an engineer.. at least not the kind relevant to this discussion. However as I understand it the knock sensors, and this is generic knowledge, it is constantly making adjustment. Generally if knock is detected it will back off a lot. It will then slowly advance until knock is detected.

The reason for this is that by making use of the knock sensor manufactures can squeeze more performance from their cars. The idea is to operated right on the edge of knock. Of course they don’t actually want knock to occur, so it will slowly advance. Of course many other factors are at play, as you change RPM the engine will need to advance or retard in response to this. Also environmental factors are at play, humidity and temperature as well as altitude. So the knock sensor has to try to adjust a moving variable to keep it right on the edge.

The way you asked the question it sounds like you think it is creating a new map to work off of, which would not be the case. It will simply advance either until it detects knock or until the programming says this is far as you can advance under these conditions.

That said some manufactures make more use of this than others. Some will advance or retard enough that you can actually see some benefit to using higher octane fuels.

As an example, and I’ll be upfront this information is very old, but I have never seen such a test repeated or done elsewhere. Back around 1990 C&D magazine did a test to see what cars could advance enough to actually make use of higher than recommended octane fuels. Back then none of the American car companies advanced timing enough for you to see an advantage using higher octane fuels. Some of the higher end Japanese makes made some use of it. but only for the next level up. Pretty much all the German Luxury cars. BMW, Mercedes and Porsche, you could put pretty much anything in and it would advance or retard enough to compensate for the different fuel.

As I recall C&D performed this test by putting the cars on a rolling dyno to measure the HP at the rear wheels. They also attached their own knock sensors to see if the engine was experiencing knock. If they saw a change in HP with a fuel with a higher octane rating they took that to indicate the car was advancing enough to make use of the higher octane. Also if the used a lower octane fuel and it knocked they took this to mean the car was unable to retard enough to prevent knocking. If the car responded to the knock be retarding the ignition enough to stop the knock they took that to mean the car could retard the ignition enough. Of course it’s possible that other factors may be at play here as well.

MikaelVroom > Scott 08/30/2016 at 15:53

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The internet is rife with generic knowledge, I was hoping for something specific from someone with their hands in the pudding. I understand the proprietary nature of the info, though, and I’m glad he was able to comment at all.

TommyGunns00 > MikaelVroom 08/30/2016 at 21:07

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Since I don’t play with Ford toys, let’s imagine the car in your question is a Camaro. Maybe it’s a 1999 Camaro. Back then, the LS1 PCM had 2 options for fuel types. If the PCM detected significant knock events, it then commanded the Low Octane Spark Table. If it detected minimal/no knock, it commanded the High Octane Spark Table. It would constantly try to advance as far as possible with as little knock as possible. Other sensors contributed to the table determination such as ECT & O2.

Now, newer ECU’s & PCM’s get even more data! You have fuel content sensors that can determine the type of fuel in the tank, and command a fully different map for fuels like E85, or extrapolate values between the Gas and Exx table so you can run any mix you like.

MikaelVroom > TommyGunns00 08/31/2016 at 09:30

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it then commanded the Low Octane Spark Table. If it detected minimal/no knock, it commanded the High Octane Spark Table. It would constantly try to advance as far as possible with as little knock as possible.

So did it switch between tables or did it interpolate between them?

TommyGunns00 > MikaelVroom 08/31/2016 at 12:15

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Old tech just switched. Made tuning for power only much easier as you could copy the high table over the low table to take out any possible variable. I wouldn’t recommend doing that on any street driven vehicle where fuel type may be an issue.

John > Bacon 08/31/2016 at 12:57

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In higher altitude areas, they don’t even sell 93. Is altitude something to take into account?

haplessmotorist > Bacon 10/29/2016 at 14:29

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What should one fo if one mistakenly fills the tank with a lower octane rated gas? Will Octane boost solve that problem? Will gentle driving solve the problem?

Bacon > haplessmotorist 10/29/2016 at 18:08

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I would carefully read the owners manual or warranty information to see if this action voids my warranty. If it does, I would tow it and drain the fuel. If not, or if the car is out of warranty, driving easy is the minimum action to take. The main point is that you don’t want the engine operating at higher loads (more open throttle) with lower than designed octane, as high levels of knock can occur and possibly damage an engine. The problem is that many modern cars will run at high load with low RPM in an effort save fuel.

So, just like this entire situation around Octane rating, it really depends on the car, which is why I say to read the owners manual. If the owners manual doesn’t specifically say to take it to the dealer if you fill with a lower octane rating, you might be ok. If this still feels too risky to you, call the dealer and ask them.

Dave the car guy , still here > Bacon 11/09/2016 at 09:09

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I have a different question. Can a knock sensor be more prone to failure if constantly sensing knock? I would think the solder joint would be likely to crack or the seal fail under a constant pounding.

Bacon > Dave the car guy , still here 11/09/2016 at 12:33

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I don’t know that level of detail regarding knock sensors. But I will guess the answer is no. The reason being that knock occurs at the natural frequency of the engine assembly (block, head, etc.). Where as the natural frequency for the knock sensor components SHOULD be designed far away from that. Also, since the peizo electric matrial is potted, it should be very robust to physical vibration. I would put my money on corrosion at the connector to be the biggest issue. But, again, this is my guess since I’m not a knock sensor engineer, so take it with a grain of salt

Dave the car guy , still here > Bacon 11/09/2016 at 12:45

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I work in GM parts now but had formerly worked 7 yrs in offshore oil exploration. We used marine hydrophones with the same peizo electric construction for those. In ours they used platinum solder because of the harsh nature of the air gun explosions used then as a sound source but it was always my understanding that the common failure point was the solder joint. Just curious. The only knock sensor I commonly sell for GM vehicles are for the 5.3 engine but most of those are due to corrosion or water intrusion from being hidden under the intake. If somebody is lame enough to pressure wash the engine it is almost certain they will need at least one of the two sensors afterwards.

Octane97 > Bacon 12/23/2016 at 13:40

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So just a double check on the numbers - I used to own a snowblower that used no ethanol 97 octane gas in, but we got rid of it. Can I place this fuel in my Subaru Forester tank which usually runs on regular 87? Didn’t want anything damaged,...thanks for this article!!!

Bacon > Octane97 12/24/2016 at 00:04

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You have a snow blower that required 97 octane? That surprises me. That is extremely high octane, which is usually used in high compression or high boost applications, pretty unusual for a modern snow blower. Who made the snow blower?

From the stand point of the octane rating, a higher octane is essentially a waste when used in car that is designed for 87 octane, but that’s it,there would be no detriment expected.

However, I would be nervous about using this fuel for other reasons. Is it old, are there any contaminants in it?

Where did you get 97 octane? Is it legal for road use (some fuels are taxed differently and for off road only). Is it leaded? What kind of additives have been used to boost the octane to 97?

Mystic20 > Bacon 01/31/2017 at 15:21

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Hello. I live in Colorado where all the “regular” gas is at 85 rather than the rest of the US, which “regular” is at 87. I just purchased a new truck (2017 Nissan Titan V8) and my manual says 87, but at most stations I only have a choice of either 85 or 91. Typically, they do not offer the “mid-grade” of 87 here and the difference between 85 and 91 is around $.60 a gallon. My house elevation is at 6400 and my work elevation is at 5800. Will I be ok with using 85 or should I spend the extra and use the 91? Will I get better MPG and/or performance with the 91? I want to make sure it is worth paying the extra $10-$15 each fill-up on the 91 if the 85 is bad for my truck. Thank you!