RustyLogic

A while ago I read CarTalk's analysis on premium vs. regular fuel; specifically, questioning whether or not you can simply rely on the knock sensor to run a vehicle that requires 91 on 87 all of the time.

According to CarTalk, you can run a premium required engine on 87, so long as it has a knock sensor and you don't hear pinging:

Premium vs. Regular | Car Talk

But the general consensus among CarTalk, my dealer, and the internet at large is mixed. So I decided to dig deeper on the matter myself, and came across some sources of information:

A Review of the Effect of Engine Operating Conditions on Borderline Knock

Fil's Auto Corner: Gasoline FAQ

The octane requirements of an engine are determined not only by its design and timing parameters, but also on the operating conditions and environments of the vehicle. For example, ambient temperature and altitude influence octane requirements.

For temperature, it seems that approximately every 7C +/- results in a change of +/- 1 ON. Which means if your car requires 91 in the summer, in the winter it would only require 87.

For altitude, it seems to be about a reduction of 3-4 ON per increase of ~1000m (or 10 kPa).

Spark advance/retard of 1 degree (360 degrees is a full engine revolution) results in a change of 1 ON.

So essentially, if you live at 3000 ft, or in cold climates, you could run a premium designed engine on regular, and the knock sensor would probably not even get triggered (assumed the engine was designed to run at sea level during temperate climates). How much closer to sea-level, or warmer, the climate you live in, spark timing would come into play.

So long as spark timing doesn't need to retard to prevent knocking, the engine should run just as well as it did on 91.

I'm running 87 during the winter here in NY. I can't tell any difference in power or gas mileage (using the Automatic ECU app).

DMZ

If you think you're being smart running your TL on 87 to save a buck or two at fill up, you're not. The 3G TL has a compression ratio of 11. That means it was designed to run on Premium fuel ONLY. I wouldn't take a chance on shortening the life of my engine which is exactly what you're doing, nor would I ever consider buying a used TL where the owner ran it on regular. We're not talking operating conditions here, we're talking about engine life.

Our mechanic in NJ, Paul, a seasoned veteran of Honda and Acura dealers, claims one of the ways I got to 220K miles is by using Premium EXCLUSIVELY. If you can't afford to buy Premium gas, you shouldn't own a TL. As much as I can respect CarTalk's article, it doesn't apply where high compression ratios are concerned. Your logic here is definitely Rusty!

My
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WheelMcCoy

I think there's something to Rusty's logic. On a skip trip, I noticed Shell Premium was only 2 cents more than Shell mid-grade, and not much more than regular although I can't recall the prices. At high altitudes, local residents don't bother with premium and the pricing reflects that. But it's a good buy for visitors who are going back home to lower altitudes.

But I see DMZ's point too. Honda / Acura has not certified doing this. It's a good hypothesis but not worth the money on testing and certification.

I don't think, however, its a question of affording premium gas with prices being relatively low. There's a geek factor in play here... one of optimization. It's what drives Prius owners to maximize their mpg. And Acura owners, compared to other premium brands, tend to be more analytical and logical, rather than visceral and emotional.

nfnsquared

How does it shorten engine life?

Makes sense to me...

FYI, the difference in price between 91 and 87 in ND is about $0.50, or about $7 per fill up. Nothing to sneeze at...

JTS97Z28

iTrader: (4)

Let's not over think this. The manual says use premium, fill up with premium. End of story.

nfnsquared

If there's no knock, how can running less than 91 octane hurt? It's an honest question...

TacoBello

Hahahahahahahahahahahahaha... Didn't two threads like this JUST get closed?

You cheap asses. Go back to taking the bus in order to save $5 at the pump, when you fill up once a week.

Where's Majofo when we need him?

TacoBello

There's no knock because your engine is retarding the timing. Doing this actually robs you of horsepower. Not too mention there is higher chances of knock occurring (even if you can't hear it). Plus it'll likely mess with your MPG, so by the end you're saving nothing and likely wearing your engine faster.

Let the naysayers say otherwise, but that's exactly why cars have knock sensors, to prevent stupidity, but it's not fool proof and it comes at a price.

truonghthe

Manufacture said "Premium" for a reason, follow it and /Thread.

nfnsquared

No, I mean if there's no knock to begin with (no retard whatsoever), how can running less than 91 cause damage to the engine?

And I've run many full tanks of 87 (over 10K miles) on road trips with zero decrease in MPGs...

TacoBello

Do as you please, man. Too many "baller on a budget" types on here.

"I want a 'premium' vehicle but I'm going to put the cheapest shit into it. Oh check out my sweet $1500 mods I did!!"

And then five years down the line you see threads like "my engine idles weird" or "my engine feels like it's lugging" popping up.

For fuck sakes... :utterlymegafacepalm:

nfnsquared

No problem. I was looking for intelligent discussion, not pure speculation and childish responses. Still waiting for someone to answer my question...

JTS97Z28

iTrader: (4)

That I have no clue, I'm not the one who said that it can hurt it, however my argument to your question is not everyone has built in stethoscope hearing. So without an instrument to tell you or loud obvious pinging, who's to say you are or are not getting detonation? So why put yourself or your car in that situation when it can be eliminated by using the proper grade fuel? Easy enough solution!
My opinion though on potential damage using regular grade fuel.....don't see how it could on a highway trip,, but would I go rowing through 4 gears on an open stretch of road with 87 octane? No.

Acura-OC

This is a very solid logic, but if live scanner doesn't report any timing adjustments only means that knock sensor unable to detect knocking but knocking actually occurs there should be loss in MPG. But if there is no loss in MPG wouldn't that mean that there is no loss in performance?

Slpr04UA6

Not Again!









In B4 the

nfnsquared

Again, I'm not questioning knock detection methods (but I would have to assume that no human can detect knock better/quicker than a knock detector). I'd have to rely on an OBD-II app or scanner to monitor timing (knock). There's no way I'd trust any human ear over instrumentation...

I would have to assume that our knock detectors are plenty sensitive enough to detect any amount of knock...

1black_seven

iTrader: (2)

I swear to fuck these threads are giving everyone cancer.

If you want to second guess the manufacturer's advice go for it.
The manufacturer gives you the required or recommended fuel grade because THEY engineered the vehicle. Hopefully with people who have a university education I'm sure.

This discussion was just locked in another forum.

AMTMJ

In my opinion, probably nothing wrong with using regular unleaded in a car that recommends premium, minus a loss in power and possibly gas mileage. That is, if the knock sensor and engine management system is working properly. My main concern would be whether the knock sensor would perform at the same level over a long period of time to minimize or prevent any knocking.

That said, saving $5 a tank would only net me another grande white mocha with an extra shot of espresso. So not really worth tempting fate in my view....

nfnsquared

Hehe, I read that thread. It was locked because people (mainly just one) started personal attacks. Hopefully that won't happen here. Just keep it factual and civil...

RustyLogic

My hypothesis right now based on articles that I've read (CarTalk, Google Scholar, etc) is that vehicle manufacturers use the words "recommended" vs. "required" according to both engine design and assumed operating environments, and whether or not spark retarding can prevent knock under all possible operating conditions.

For example, manufacturer might assume the vehicle to be operated between -20 F to 120 F. Altitudes -300 ft to 12,000 ft. Weight loads +80lbs to +1,000 lbs. (For typical consumer).

If a high compression engine design with the knock sensor permits the vehicle to operate without knock in the full range of conditions by adjusting timing, then the manufacturer puts the label "91 recommended."

If the engine design with the knock sensor permits the vehicle to operate without knock in a subset of the full range of conditions, then the manufacturer puts the label "91 required."

As an observation, if you examine the new 2015 TLX, there are two engine types:

Compression 11.6:1: 4-cyl.
Compression 11.5:1: V-6 & SH-AWD

The 4 cylinder engine has a fuel label "91 recommended." The V-6 has a fuel label "91 required," even though its compression ratio is technically smaller. They both use the same mechanisms to compensate for varying octane number and operating environments: knock sensor with spark retarding. However, the V-6 model is also 300 lbs heavier than the 4 cylinder model. I'm sure its operating temperatures may also be higher than the 4 cylinder, since I assume 6 cylinders generate more heat than 4.

So obviously, compression ratio is not the only mechanism at play. If added weight and heat means the vehicle can operate without knock only between -20 F to 80 F and easy driving (reduced heat generation), instead of the full range of -20 F to 120 F and intense driving, the manufacturer would write "91 required" as opposed to "recommended".

So in summary, I believe that if your engines operating conditions (easy driving, high altitude, or cold temperatures) are within the range that either knock is altogether avoided, or the engine can compensate through timing and knock sensor usage, no long term engine damage occurs, and your vehicle is fine running on regular 87 octane.

Some top-tier gas stations put the same amount of engine cleaners in their 87 octane as in their 93, as well. Mobil is one such station:

Which gasoline is best for mileage, your car's engine and your wallet? - ABC15 Arizona

Mobil even advertises that the only difference between their 87 octane fuel and 93 octane fuel is the octane level:

Types of Gasoline at Exxon and Mobil Stations | Exxon and Mobil

The difference between 87 and 93 here is $0.60 per gallon. If one can reasonably conclude that under their specific operating conditions knock will not occur, even without the knock sensor retarding timing (because it's cold, high altitude, or easy driving), and the fuel detergents are the same between 87 and 93, it is unlikely that use of 87 octane fuel would cause any engine damage whatsoever.

polobunny

I love how these threads are full of answers from people with some general knowledge and how they like to second guess manufacturers requirements to save a penny.

The requirements are there for a reason and obviously they will not apply for all situations as noted in the first post.
Are you the kind of person that is going to risk either expensive repairs or cutting your engine life in half for a handful of dollars without knowing if it's safe for you to use regular vs premium depending on many factors which you cannot really calculate because of the lack of knowledge on the matter? Go ahead, be my guest. Your uneducated guess is as good as mine.

Personally I don't consider ever putting regular in my TL, not because I'm not cheap (believe me I am!), but because there's no way for me to make sure it's going to be safe for the car.
Also if it doesn't rob you from mpg, it's going to rob you from power. This isn't magic.... Can't make more with less...

nfnsquared

Theoretically, either of those would only happen if timing is retarded/pulled, correct?

Steven Bell

iTrader: (2)

With gas prices the way they are now, surely you can afford Premium.


I just paid $1.93 for Premium yesterday in Kansas City.

polobunny

I believe that is the case. Using 87, 89, 91, 93 or even more won't have any effect if you do not change any other parameter. So unless timing is retarded/advanced (assuming all other parameters are the same and no detonation occurs) then nothing will be different.

But like said, uneducated guesses are just that. I for one will not risk detonation by running 87 in a 91 required engine neither do I want the hassle of continually monitoring if timing has been retarded to see if I'm losing power.

Also once the knock sensor has sensed knock... it's too late, it has happened. It doesn't magically guess when knock/ping is going to happen, it already has, all it does is simply adjust in hopes it won't happen again. It is very sensitive, more so than any human ear, but it's not a knock preventer...

nfnsquared

OK, that's what I thought as well.

DMZ

$2.07 here in New Jersey!
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RustyLogic

This is the case for both "premium recommended" (no damage to engine) and "premium required" vehicles (damage may occur in extreme operating conditions). Inaudible pre-ignition is not detrimental to the engine.

Premium vs. Regular | Car Talk

Also, the operating point at which pinging/knock occur can be predicted -- not by magic, but by mathematical models of the operating conditions.

http://papers.sae.org/922324/

DMZ

Knock sensor smhock sensor! Your car. Your money. Your engine's longevity.
The recommendation of the engineers who designed the car who have nothing to gain by telling you to buy Premium fuel.

End of story !
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04WDPSeDaN

iTrader: (1)

Waiting for those TLX guys to come in here and tell us its ok to use regular because it's only a recommendation not a requirement. I don't care what type of engine you have. Using 87 is terrible.. Period.

Gasoline isn't 100% pure anymore and hasn't been for a long time. Most people are hung up on two perspectives 1. Performance 2. Fuel economy. Beyond these two basic lays more than that. Carbon build up is number 1 to lowering the efficiency in any engine. Prolong term of carbon build up can cause accelerated wear on internal parts. This also works with the amount of carbon produced through the exhaust which has fouled out 02 sensors and clogged cats. This can also throw air/fuel mixture off. Running too rich or too lean. Not good for any engine.

Using 91 or higher (top tier) has nothing but benefits. With higher compression engines it's a no brainier to use the highest octane possible. The TLX now offers direct injection. You would be an idiot to use 87 in a direct injection engine. It's NOTORIOUS for carbon build up. Most German cars require carbon cleaning and recommend the highest octane possible to help control the amount of carbon build up. KIA's GDI engines also run the same way with direct injection, in fact, in the user manual it says to use a fuel system treatment every so often to help control carbon build up.

In the most basic form, carbon build up is exactly like clogged arteries in your body. Knock is a very known way to blow an engine. Just because it doesn't let a rod loose right away doesn't mean it's still ok. For us that are running force induction (I'm supercharged) one of the biggest fears is knock. Control knock, use highest octane and tuned right no worries. Again, it's not hard. A healthy body requires quality, clean food and water as the same with an engine, quality gasoline and proper maintenance goes a long way. What would I know, an enthusiast, car guy, and an ASE certified technician for Acura over 10 years.

As always, In before it's locked. /thread.
Majofo for president

polobunny

Inaudible pre-ignition is likely not detrimental if it happens on occasion. Probably is if it happens often, which once again, you have no way to know unless you monitor yourself or the car tells you with bright flashing lights.

This CarTalk article is just another article on the internet. Without sources, it is useless. The opinion of another guy on that topic, as good as yours or mine.

The risk is real, and the same CarTalk article goes a long way to discredit the use of premium fuel, as if the only situation it was applicable to use premium fuel was "If you plan to haul that aforementioned mother-in-law in hot weather, or are going to be driving up monstrous mountain passes with a heavily laden car, then you might consider filling up with a tank of premium gas." once again without any further data.

It is dangerous for anyone to believe such bold and vague statements, in my opinion. Pretty irresponsible.

As for predicting when pinging or knock can occur, obviously it is possible. Your car knock sensor however does react, does not predict.

Believe it or not, car manufacturers have all the reasons to make you use less gas or pay less for it. They'd rather have you buy their car than the competition's car, so it would be pretty silly for them to require or recommend premium fuel if they knew you could run it on regular without any risk or downside.

DMZ

Yeah, lets see how many TLX guys there are out there because I've seen just a scarce few on the roads, very very few to be exact. Meanwhile, I see 2013/14/15 Accords EVERYWHERE I look, literally! And hey, those engines were designed to run on regular!

04WDPSeDaN

iTrader: (1)

For those wanting to do Automotive 101 class. Read and understand, again, beyond two perspectives of Performance and MPG.


Effects of carbon build up
A properly tuned engine is required for optimal engine performance. Unless the vehicle is tuned to factory specifications,catalyst and emission related problems including catalyst efficiency codes can be triggered.

Today's tune-up no longer simply consists of replacing plugs and checking fluids. Due to tighter engine tolerances and more sophisticated controls, additional work may need to be performed to prevent and correct emission related codes.

How Does Carbon Build-Up Affect Engine Performance?
As the engine operates, carbon deposits may form in places such as the valves, ports, pistons, head gasket and piston rings. This carbon can interfere with normal combustion is several ways. It can alter the engines operating temperature, compression ratio, and several other important factors involved with combustion and sensor readings.

How Can Carbon Alter the Sensor Readings?
The carbon contributes to abnormal combustion in several ways, but the most dramatic effect in a modern fuel injected engine is the "sponge effect". As the fuel mixture in the cylinder is compressed, the carbon has a tendency to absorb both oxygen and fuel. Once the ignition spark fires, the flame front normally spreads through the chamber, consuming the fuel and air, however, the carbon has a tendency to extinguish the flame front and stifle combustion.

This, combined with the fuel and air that was absorbed, results in poor efficiency. As the chamber decompresses during the exhaust portion of the stroke, the unburned fuel and air is released, resulting in both excessive fuel and air (containing oxygen) entering the exhaust system. The O2 sensor detects the excessive oxygen and the vehicle computer (ECM, ECU, PCM) compensates for this by enriching the mixture.

This causes poor catalyst efficiency, and increased carbon formation. The situation is aggravated by the overly rich mixture, resulting in the engine's failure to reach a sufficient temperature to remove these deposits. In addition, the excess fuel can permanently damage the catalyst or cause meltdown (on the outlet side as opposed to the inlet) and can get hot enough to melt stainless steel substrates.

Does Carbon Alter Combustion in Other Ways?
Absolutely, in addition to causing poor combustion, excessive build up can also alter the vehicle's compression ratio. The carbon fills up spaces around the piston rings, head gasket, and spark plugs. This decreases the amount of space that is available in the combustion chamber. This increases the compression, which can cause the engine to overheat, ping (detonate), and also causes an increase in NOX emissions. Due to the fact that the carbon can retain oxygen from the combustion process, it can cause another interesting effect that can cause the vehicle to either trigger a light or fail an emissions test.

A catalytic converter requires certain conditions to break down harmful emissions. It requires a slightly rich mixture and a low oxygen level in the exhaust system to break down NOX. Because the carbon causes increased NOX emissions and also causes excessive oxygen to leave the combustion chamber unconsumed, this actually impairs the catalyst's ability to remove the NOX from the exhaust.

Article on Direct injection VS fuel injection and VS a clean running direct injection vs one that is clogged with carbon.
DailyTech - Direct Injected Engines from Some Automakers are Seeing Reduced Performance

Another good article on causes of carbon build.
http://autorepair.answers.com/fuel/p...arbon-deposits

nfnsquared

^^^^ What does that have to do with 87 vs 91 octane?

JohnDoe2

You will lose a bit of horse power.

That is all that will happen.

Your car will not explode into a burning fireball killing orphans and nuns. So chill out on the histrionics.

04WDPSeDaN

iTrader: (1)

You're not serious, right? Didn't I just say that most are only looking at the topic as performance vs MPG. To understand the entire reason of why you would use 91-93 vs 87 goes beyond that. I'm not here to teach Automotive 101, I paid plenty of money for my education and continuing education in the automotive industry. I'm not here to spoon feed you either..

04WDPSeDaN

iTrader: (1)

Thanks

nfnsquared

Yes, I'm serious. I think we all agree that carbon build up is bad and is even more of an issue with DI engines.

But what does carbon build-up have to do with using 87 octane fuel vs 91 octane fuel? Carbon build up is accelerated by poor quality fuel (e.g fuel with inferior additives), not by lower octane....

04WDPSeDaN

iTrader: (1)

Nothing at all.. Good night.

TheChamp531

iTrader: (3)

Another gas thread. /facepalm

Always annoyed that people always try to find a way to justify their beliefs with consistent settings and saying it is OK. Nothing is consistent in nature. You put your car in a perfect setting and 87oct is OK. We all know it isn't blue skies and sunny everyday. Just put the 91/93 octane and be confident that your car has a better chance of not failing than putting in 87. That is all I need to know for me to put the higher octane.

RustyLogic

For those who are inspired to read and learn:

http://www.powerstyle.ru/docs/ebook.pdf