Originally Posted by Mike_TX

Well, I should have expected to get beaten up for saying using Premium isn't necessary. It's such an emotional thing for some reason.

Octane is just a measure of a fuel's resistance to knock. Period. It's NOT a measure of its power. Sorry, it's just not, despite what you might have been told.

Per the Consumer Energy Center:
"There is little difference in energy content of regular versus premium gasoline. They both contain about 111,400 British Thermal Units [btu's] of energy per gallon."

Here's the skinny: Your engine has computer-controlled timing/spark advance, combined with knock sensors that listen for detonation. The system actually "tunes" your engine on-the-go, and adjusts for differences in gasolines as well as altitude, temperature, and other factors.

Acura recommends Premium fuel for a couple of reasons:

1. They have paid a ton of money and spent thousands of hours getting their engines certified by the EPA and other agencies for a given fuel. It's a costly and time-consuming process, and they don't want to do it for 3 different grades of gasoline. Plus, gasolines can vary a little from state to state and area to area, further complicating things.

2. They're playing it safe. They are responsible under warranty for repairs to your engine, and they understandably want to give themselves all the wiggle room they can. So they recommend the "best" fuel they can, and Premium generally has a better chance of having detergent additives than Regular. Top-Tier gasolines have the same detergent additives in all grades.

But it's still significant that they changed the language from "Required" to "Recommended".

People still cling to their old ideas about gas and don't want to listen to facts. I guess the gasoline company advertisements have been really effective. :wink:

Originally Posted by insanik

lol what!? Competition? the TLX competition is A4, BMW3, benz c-class...

All of these use premium.

Even brand new KIA optimas say regular gas is fine but eventually causes issues.

it's just FACT that cars run better, and perform better, and have better longeivity with premium fuel


People who are trying to save a buck at the pump shouldn't be buying premium cars if they can't afford it.

Originally Posted by vbx

So how are they saving money if they're getting less MPG?

On the Infiniti Owner's manual for my G coupe. It says I can use Regular if No Premium is available. But Warns me not to smash on the gas and to fill it with Premium asap.

Originally Posted by SL1200MK4

At this moment probably only the engineers at Honda/Acura knows the answer. But we will also soon find out once someone experiments with their own car. There are a few things of interest.

1. Can the car run on regular fuel without knocking?

That's is the most important question of them all and we got two engines to experiment with.

2. Does the engine produce less power with regular fuel? If so, by how much?

In most cases with a higher octane tune, the most dramatic increase in power is at the upper revs. So, even if you make 10-15hp less peak horsepower, you might not even notice that in your daily commute driving in the lower rpm range.

3. Does the engine run less efficiently with lower grade fuel? If so, by how much?

Premium fuel cost about 13.5% more than regular where I live. If my fuel economy goes down by 5% running regular fuel, it is still the financially sound choice.

Originally Posted by joeddmd\

However, if I was leasing I think the 87-89 octane argument makes more sense. B/C it wouldn't be my problem.

Originally Posted by fsttyms1

1. Unless you have a live data reader to read if the engine is detecting knock and or really pulling timing you wont know or be able to experiment with.

2. Yes, more loss will be higher up, BUT It will produce less power across the board. Knock doesnt need you to have your foot buried to the floor board to happen,

3. ??? I know in my old J32a2 and my J37 I saw on average 40-60 miles less to a tank (mixed driving) running 87 with 10% Ethanol. In the end, It cost me more to run Regular than to use the more costly 93.

Originally Posted by tsturbo

You are one reason I would never buy used

Originally Posted by Mike_TX

I've been using nothing but Mid-grade in my RLX for 9,000 miles, with no knocking and no ill effects. Also ran it in my RDX for about 15,000.

I know that's not long enough to tell a lot, but I also get 21mpg in town and I've seen several tanks on the highway at over 33mpg.

The car seems happy with it and I save 3 bucks a tank. That adds up.

If you want to run Premium, by all means do so.

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Originally Posted by SL1200MK4

Get a Bluetooth OBDII reader for $10 on ebay, download the Torque app on an Android device and have fun.

This debate is all about the issue of "bandwidth", a term Porsche Engineer Andreas Preuninger uses. In other words the flexibility of the operating range of the engine.

The engine can tolerate a certain variance in ambient temperature, for argument sake let's say -40C to 50C. It probably won't run very well in extreme hot and cold temperatures but it will work.

Like ambient temperature, the engine can tolerate some variance in the fuel with respect to octane rating. Maybe it will absolutely choke on regular fuel and the world will end, or just maybe that it will run reasonable well with regular fuel without any long term repercussion, or maybe mid grade is as low as you can go.

Not that I am advocating the use of regular fuel, but money is on that it won't hurt.

Originally Posted by Stew4HD

600k miles?? wow! Commendable and very impressive, for sure!

Originally Posted by ggesq

Agree- if I were to ever buy a used car and found out the owner was too cheap to put the recommended or required fuel in it...pass.

Originally Posted by I hate cars

The reduction in gas mileage is due to the timing being retarded from knock and from the knock itself. All grades have about the same burn rate and amount of energy. Premium is more resistant to detonation. Detonation by itself can hurt mpg because you don't get the in cylinder pressure rise at the right time. Preignition by itself can hurt mileage by trying to push the piston back down the wrong way, not to mention the actual power stroke is pretty much wasted, the same as a misfire. Couple that with ignition retard that the ECU uses to protect the engine which can cost 10-20lbs of torque and several mpg. More ignition advance allows the engine to make the most of the air/fuel it already has. Retarding the timing means you have to give it more throttle for the same output, reducing mileage.

The difference is large enough that it's cheaper to run premium most of the time, especially in hot climates and drivers with a heavy foot. If you were super broke like I have been in the past and payday is just a few days away, filling up with regular can save some money in the temporaril but you'll be filling up slightly sooner. I've been so broke trying to put myself through college that I've had to pull the wastegate off the GN so there was no boost and I ran it on 87 for the better part of a year. Of course, I seemed to pull up to every fast car in town once I had no turbo.

To the OP, nothing will happen with a tank here and there of 87. The engine damage from running 87 octane is cumulative meaning you're not going to suffer a catastrophic failure, but you might see increased cylinder/ring and rod bearing wear over the course of 200,000 miles.

Originally Posted by I hate cars

I don't think you understood what I said. I named the reasons why you lose power and mpg on 87 and energy content was not one of them. I'll summarize one more time:

Detonation by itself causes a loss in mpg and power

Pre ignition by itself will cause a loss in power and mpg.

The timing retard that's a result of the ECU trying to protect the engine from detonation will really hurt mpg and power.

This has nothing to do with energy content and premium does not burn any differently than regular.

Originally Posted by I hate cars

I explained it twice now. Forget energy, you're focusing on energy and completely missing what I'm saying. The burn rates and energy are nearly identical between 87 and 91.

Ignition timing leads the piston to TDC. The air fuel is ignited before TDC based on combustion chamber design, load, and piston speed along with many other factors such as compression ratio, temperature, and octane to name a few. The point of leading the piston and igniting the mixture while the piston is still coming up in the bore is to attempt to get the majority of the cylinder pressure created by combustion at 14 degrees after top dead center. This might mean leading the piston by 20 degrees before top dead center. When the pressure peak occurs before or after 14 degrees, power and mpg is lost.

When there is detonation caused by low octane you usually get the peak too soon and instead of a controlled burn you get an explosion which is the pinging sound you hear. This in itself costs power. The energy content of the fuel is irrelevant.

When you experience preignition you not only ignite the air fuel mixture too soon and try to force the piston back down the wrong way which costs power, you also lose most of your power stroke because the pressure peak occurred at the wrong time so you're not contributing to power, you're losing power.

If it's not bad enough that you lose power from detonation and preignition by themselves, the ECU also steps in and retards timing to protect the engine from damage. This means the plugs are firing later and your in cylinder pressure peak is occurring too late. You lose both power and mpg from late ignition timing. Again, energy content plays no role here. You're igniting the mixture too late in the combustion stroke and evidence of this can be seen in exhaust gas temperatures. They shoot up when timing is retarded because you have some of the still burning mixture being pushed out of the exhaust instead of making power.

As I said in my first post, how much running 87 octane affects you depends on driving conditions such as city vs hwy, how heavy your foot is, temperature, etc. I used to make a 4 hour trip to Vegas twice a week for a couple years and before that I made a trip to Fresno and back which was 210 miles round trip a day for Fresno and 540 miles round trip for Vegas. All freeway and I always made the trips at the same time, went the same speed on cruise control, in both summer and winter. I thought there wouldn't be much of a difference under light load of the freeway but after running it on 87 a couple times in pure freeway use, it didn't take long to realize it was cheaper to use premium. It most definitely makes a difference in mpg in the real world.

You can't just use 87 octane and switch to 91 and compare with just two tanks of fuel. Inaccurate's observation of the knock system showed it can take a day or more to put full timing back in.

So don't worry about detonation and preignition causing the loss in power. Just remember that our 11:1 compression TLs will pull timing on 87 octane and less timing means a loss in mpg and power. You can google ignition timing and mpg if you like.

Originally Posted by I hate cars

Air fuel ratios are irrelevant, they stay the same regardless of octane.

Detonation decreases power and mpg.

Pre-ignition decreases power and mpg.

Pulling timing decreases power and mpg.

The combination of timing retard and detonation or pre-ignition results in lower mpg and power.

I don't know how many times I have to repeat myself.

How can the octane not matter in a car that's designed to run on premium? If it makes no difference in power and mpg, why do they suggest premium? It's certainly not to increase sales.

Being able to run regular without damage is not the same as being able to run regular and retain the same mileage and power as premium. Some "forum members" have access to people in the industry and not google, along with their own research. I've done the long term mpg tests under very repeatable conditions. I've done the research with the scanner hooked up to verify the TL most definitely retards timing on 87. It even retards the timing on 91 a little.

I thought you of all people would understand what retarded timing and detonation would do to mpg and power but you will disagree with pretty much anything I say so I totally understand where you're coming from.

Since according to you there's no decrease in power and mpg and it's perfectly safe to run on 87 octane, do you suggest every TL owner run on 87? What do you have in your tank right now?

Originally Posted by I hate cars

If you can answer the question of why power is reduced when you run a lower octane in a car that requires premium, you might be able to apply that to the mpg loss as well. Let's see if you can make the connection.

I might as well give you the answer. So, when timing is retarded, power is lost. To counter that loss in power the driver must give it more throttle. More throttle equals more air and fuel being burned. It's not making best use of the air and fuel it has because timing is too late and the in cylinder pressure rise comes too late. You're burning the same amount of fuel but you're making less power with it.

You can not have a loss in power due to timing reduction without a corresponding loss in mpg.


So again, you get worse mpg and power for a few bucks at the pump. You're talking a savings of $4 on a fill up. Are there really people out there that own a TL that are so cheap that they can't afford an additional $4 twice a month even when it means filling up less often? You're talking a
5-8% difference, something that can easily be made up in the mpg department.

Originally Posted by I hate cars

As I said earlier (this is the 3rd time I'm repeating myself in one thread), the conditions in which 87 is run have a huge influence on whether or not you can get away with it. Temperature, driving style, speed, etc all have an effect. I too drove my car at about the same time of day, filled up at the same station and made the same 460 mile trip twice a week, I even posted on it back in the day on here. I was surprised there was a mpg difference in 87 and 91 under light load. Temps were generally 90-113 in the summertime and there were some mild hills.

Taking off from a redlight requires 2-5x as much throttle as cruising at 70mph. Unless you can cruise steady state on flat ground in 60 degree weather, you will see a decline in mpg on 87 octane as I did. To take it a step farther, I got another boost in mpg when going higher than 91, showing it's still pulling timing even on the freeway on 91 in my conditions.

Also to add to my experience was driving for a couple weeks with the scanner hooked up monitoring knock retard and there most definitely was timing being pulled.

Originally Posted by I hate cars

You forget one huge point. Those with the very high compression ratios are direct injection which allows substantially higher compression and boost on a given octane. That's the number one selling point of direct injection. You can't compare our port injected TLs, it's apples to oranges.

It is not a theory that the TL detonates on 87. I've had the scanner on it. Hell, it detonates on 91 octane under the right conditions. Others have seen the same thing. The TL detonates on 87 octane period. If you have 87 and you're driving normally, the knock sensor is working overtime.

It is not a small difference between 87 and 91 when you have a car with port fuel injection and 11:1 compression that has some detonation even on 91. I'm the original owner and I've been forced to run about 4 tanks of 87 since the car was new, usually due to poor planning. The car surges and feels gutless when you attempt to drive it normal. It feels ok as long as you put your foot in it and you keep rpms above 4,000rpm.

Originally Posted by Mike_TX

Originally Posted by hddnav

My experience has been that I usually don't mind pampering my car with premium gas when it's still relatively new and interesting, but I find it distasteful after my emotional attachment to the car has worn off. At that point, my car is essentially a transportation appliance, and having to gas it with premium seems like a cost that really benefits only the manufacturer, who can claim higher HP and MPG on their EPA estimates with an under-designed engine, at the expense of the owner.

I'm not yet at that stage with my 3.7L TL, but I'm sure that, in the future, I will become tired of the "premium-only" requirement (not recommendation) that it has.

Originally Posted by ggesq

some great info IMHO from IHC on the topic:



Taken from this thread so you can see the full description and not just my quotes: https://acurazine.com/forums/showthread.php?t=905959

Originally Posted by fsttyms1

The 3.7 isnt something that i would do that on If you had the 3.5 i wouldnt have as much of an issue saying im sure you could get away with it.

Originally Posted by hddnav

I didn't say that I would actually NOT put premium into my car. I just said that I could picture myself being slightly irritated at having to do so.

My previous 2005 Subaru Outback XT had a turbo 2.5L engine that *REQUIRED* premium. My 1997 Integra GS-R, with a 8100 rpm redline, recommended premium. Both were bought brand-new, at the time.

I believe that my 3.7L TL *REQUIRES* premium.

I'm just speaking from experience .

Originally Posted by technoarch

For what it's worth (not much). Our salesman this past Monday was very excited to show us on the gas door that premium was recommended and not required.

....yeah OK.

Originally Posted by fsttyms1

Just giving my advise.
Oh, And im just speaking as someone who has built a 3.7 from the ground up

Originally Posted by MardiGras

Right. And correct viscosity motor oil is recommended, but not required.

Originally Posted by technoarch

Totally agree, was just surprised that the salesman was talking it up so much. I mean, really talking it up like it would make or break a sale.

We didn't even bring up the question of the fuel type.

Originally Posted by fsttyms1

2. Yes, more loss will be higher up, BUT It will produce less power across the board. Knock doesnt need you to have your foot buried to the floor board to happen,

3. ??? I know in my old J32a2 and my J37 I saw on average 40-60 miles less to a tank (mixed driving) running 87 with 10% Ethanol. In the end, It cost me more to run Regular than to use the more costly 93.

Originally Posted by hddnav

Whether fuel type is a factor in the purchase decision all depends on whether the buyer is stepping up from a non-premium brand (such as Honda or Toyota). This type of buyer is most likely working middle class and will be weighing the advantages of a premium brand, such as Acura, against its disadvantages (which can include the fuel type requirement). Face it - if you're "rich" or "independently wealthy" and wanted a car to reflect your "status," you wouldn't even give Acura the time of day.

This is where a brand like Acura doesn't command the respect that Lexus or BMW do. Acura isn't necessarily targeting the luxury car buyer (the "if you have to ask, you can't afford it" crowd), but hinges its hopes on people who would like a nicer Honda. Honda people are usually "smart" shoppers who are price sensitive. It's also no secret that, except for the 3.7L engine, most Acura engines are more or less straight copies of those in Civics or Accords, with different ECU programming to increase compression to eek out the extra 15hp over the Honda.

This is very apparent in the sales failure of the RLX, and the fact that the TLX starts at $31k MSRP (which is strictly Honda territory). The market that the TLX competes in today is also much different than before, with efficient luxury Hybrids (for example, GS450h) that are both techy, sporty, and efficient.

Originally Posted by internalaudit

It probably matters less with Americans were the premium is 20 cents a gallon, someone pointed out that it's 60 cents a gallon difference here in Canada.
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Originally Posted by exl_ent_v6

i saw someone post this too -$.20/gal extra... i wish it was like that. Maybe in some parts of the country but not NY or FL. It's more like Canada - 50c+ over regular.

Originally Posted by ggesq

+1, this morning filling up...regular was 3.19 and premium was 3.61. FML.

Originally Posted by internalaudit

Because they are using regular instead of premium?

Originally Posted by vbx

But if they have to fill more often, its not really saving is it...

Again, there is no point in using premiun on a car that runs on regular. That's a waste of money.

Its funny really. U go to a civic forum and they want to run premium thinking they get better performance. Then u go here and people want to use regular thinking they will save money.

If acura says premium fuel recommended, then u can use whatever the hell u want. Jusr read the manual and see what it says.