dano806

My question is one which has been raised many times, but never answered to my satisfaction. I realize that Acura states that the TL requires a minimun of 91 octane. But why, will the car perform poorly with less ocatane? If a person would run 89 octane would the engine performance be so adversely affected that it would be noticeable to the driver?
What specifically is the reason to burn such a premium octane?

TireSmoke

the short answer? Octane is a measure of how easily the fuel will combust in the engine. The lower the octane, the more easily it will ignite. If you run fuel that is too low, it's gonna go off to early because of the high pressure in these performance engines. You'll hear knocking, which will be a sign that the fuel is igniting too early. This affects performance and can damage the engine.

VTEC=happiness

Not only would the performance be affected, but chances are that the the engine may begin knocking and the gas mileage will decrease. It will actually save you money long term to pony up a couple of bucks extra with every fill up.

oneilc

To elaborate on TireSmokes answer check out this link http://auto.howstuffworks.com/question90.htm

rets

If you like to read more, here is another one... http://www.acura-tl.com/forums/showthread.php?t=80062

dano806

Thanks to all who replied. This is the place to go when in search of the answer. I now thoroughly understand the higher octane requirement. Vrrrrrrrrrrrrrrooooooommmmmm!

TLMike

One additional question related to this. I'm finishing up the process of getting a TL here in Colorado (6MT non-navi, Anthracite/Quartz or Black/Ebony) and one dealer I talked to actually said not to use 91 octane. He said at higher altitudes like Denver's, they've had problems with 91 octane -- some TL's have the Check Engine light come on or have problems starting. The service department recommends using 87 octane. Has anyone else heard this?

rets

"MIL (Check Engine Light)" and "hard to start" are quite common issues for this car, and Acura has come out choices of solutions to fix most of them. This is first time I've ever heard that Denver's dealer told you "altitude" factor. Interesting.

Please have us updated if possible. Thanks.

SidS1045

To follow up on that, what modern engines do when they hear knocking (yes, there are sensors in the block that can detect knocking) is retard the timing. Thus, you may not hear any knocking with lower octane gas, but you will lose engine power.

Road Rage

I have a Honda engineering study for the NSX, and the variance between 97 and 91 on that car was not as high as you might expect - less than 8 in HP/torque. So, if you are driving on the Interstate a lot, 87 makes sense. The car will retard the timing just enough to avoid ping. But if you run 87 all the time, the loss in power could add up.

The other thing is that most fuels run ineffective amounts of detergents, but generally put more in their premium fuels. So if you run 87 regularly (no pun intended), then use of a quality, low intensity injector cleaner like Red Line's SI-2 is recommended.

And remember, gas does not explode - it burns in the combustion chamber.

TLMike

Some follow-up on the altitude issue. Mile High Acura in Denver had told me that they were recommending 87 octane for TL's in Denver. When I asked the same question of the Courtesy Acura Service Department, they said they had never heard of such a recommendation and stand by using 91 octane. I'm wondering if Mile High was just using that to ease concerns about high fuel prices. Anyway, onto something more important...

I picked up a SSM/Ebony 6MT from Coutesy Acura last Thursday. I'm finally an official member of the club. And yes I changed my mind on color. I was at Courtesy and the SSM TL just came off the truck -- first SSM I had seen in person. It was love at first sight. I also liked that it was still in the wrapper.

rets

Again, welcome to the club...

Dealers used to "tell" what they like customers to know. Glad to get this issue updated, thanks.

(Only two posts, you had lots of patience, man. 8/4 and 8/16. )




ENJOY.

cvajs

did you ask them if they knew what octane was and what it is used for?? you would be surprised as to how many dealerships know very little about how the car really works. the ECU will adjust air/fuel mixture accordingly, but it cannot compensate for the low octane fuel that is being compressed (compressed in a engine DESIGNED for the higher octanes)!!

cvajs

sole purpose is for engine control. the systems around the block & pistons are designed to control various aspects of the engine. one variable built into their equations is the fuel, namely pump gas (which has various octane ratings). the whole package is designed to produce max power while maintaining control that is likeable to the driver. with as much fuel as the TL takes in, i could build a Buick 231 V6 engine that would be killer, but the ride would feel like a ride in a old Mercury missle to the moon.

cheers

argoldst

I just wanted to add that I remember reading a article (I think it was car and driver) that wrote up about it.

Anyway, to make a long story short, the conclusions that unless your car is really high performace, it will make no difference to use a lower octane.

I remember cars like the m3, or amg models of benz would have problems with lower octane. But most cars had no problems.

With the acura tl, I think it would fall under the same catagory and I think using a lower octane would not cause any problems.

cvajs

this is not 100% true. it all depends on the compression ratio. if with no spark at all the engine diesels, then no ECU adjustment will make any difference.

if the outcome of a "burn" produces lots of heat and pressure in a short period of time, that's a explosion. explosions are controllable in many ways, and the "golden egg" is in the burn kernel.

cvajs

you are quoting generic street terms to describe compression ratio of the engine.

this is not a guessing game decided by if someone claims your car to be high performance or not. i'm no engine engineer, but i have alot of physics under my belt.

the engineers of the engine know what the compression ratio is, what fuel to use, and as such use generic terms in the owners manual such as "recommend", etc. for those who don't abide by the recommendations, please let us know what your experience is using non-recommended fuels.

i don't even get the reasoning behind the argument. if 87 produces less power that means you'll need more fuel to get the job done. why then bother with 87 ???

sure 87 will not kill the engine, but there could be severe consequences.

Snive

there are two main items in this post.
1. I hate to disagree with RR (pretty much wouldn't want to disagree with anyone who's name includes "rage" in it), but gasoline does explode in your engine.

That's the whole premise behind how internal combustion engines work. Ok, it's actually the pistions interaction with the explosion that is the bulk of the premise.
If it didn't explode, nothing in the chamber would try to expand. If nothing tries to expand in the chamber, then the pistons wouldn't move. We all know it would be a bummer if the pistons weren't being forced to move by some means.

explode: To release mechanical, chemical, or nuclear energy by the sudden production of gases in a confined space;

Poor guy wrote an entire post, and I only reply to one mis-statement in it. Sorry about that.

2. As compression ratios increase so do the internal temperatures of the combustion chamber. 87 octane fuel in the acura's engine will explode earlier than 91 octane. Which means you won't be at the proper position in the piston's stroke when the explosion occurs. Thankfully the acura can adjust the timing of the spark plugs so they can help ignite all of the fuel when it's burning too early. However, all that adjusting for the lower octane fuel does mean your engine is running below it's peak performance. As some others have mentioned it is using fuel it wasn't designed to use, which means it is burning the 87 octane less completely than it should.
On a side note, my SLK will actually retard the vehicles engine if you run less than 91 octane, once it figures out that you've messed up with the gas. Actually it's not so much that it's measuring the octane of the fuel as it senses knocking, temperatures, exhaust and so on. Once those parameters get out of whack, it limits the speed to 60mph, and limits the acceleration too. At least that's what I've read, I haven't tested it myself.

But why would one get the TL instead of the TSX if one is intent on using 87 octane?
I can't think of a single benefit the TL offers to someone who would knowingly using 87. I mean, one would use 87 either for financial reasons or for enviromental reasons. Neither of which make sense in the more expensive, less efficient TL.

TLMike

Rets -- sad part is I've been looking since February and finally pulled the trigger. As for posts, I'm sure that will increase now that I actually have the car. I don't like to comment on things when I don't have any basis for making comment! This is an incredible resource for information. I was definitely more educated when I finally made the purchase.

cvajs

correction, i think we both missed his point. RR is correct in his explosion analysis. the fuel actually burns. the features of the burn is what defines the explosion. hence, gas spilled on the ground and lit won't "explode".

Scott GN231

The reasoning is as follows, you will not knock under normal driving conditions with 87 and will spend less $ per mile.

87 octane fuel does not produce less power simply by virtue of being 87 octane, though it is more likely to pre-ignite, or detonate, under high load. When this happens, the knock sensor will hear the detonation and the computer will pull timing to prevent more detonation from occuring. It is this retarded timing, not the octane rating itself that makes the car perform less well on lower octane fuels.

Cruising along the highway, no timing is being pulled and you're making the same power that you would on 91 (or 110 octane).

Assuming your knock sensor is operational, you will not hurt the motor by driving with 87 octane-- the computer pulls timing until no more detonation occurs.

Not sure what Cvjas is tring to express, though he's right about being able to build a Buick 231 to go fast (on 110 octane, with a just little boost... )

Scott

Snive

Yes, gasoline on the ground doesn't explode. That's liquid gas.
Liquid gasoline burns.

Gasoline mixed with air, well mixed with air, such as when sprayed out of an automobile's fuel injector as a very fine mist, explodes.

Concentrated gasoline vapors explode.

FAE (Fuel Air Explosive) bombs explode,

Natural Gas or oil, when sprayed out of a home furnance's injector as large droplets, burn.

You can read more about internal combustion engines here - i hope this link works.
http://auto.howstuffworks.com/engine1.htm

page 2 and 4 should help to clear up any confusion as to whether the gas actually explodes. Just remember, if gas doesn't explode then what do you think forces the piston to travel and provide mechanical engergy to your drive train?

cvajs

1) i'll make my point again. if the fuel starts to diesel, then it does not matter how much timing you pull. you definitely don't want this to occur. in engines with higher compression ratios, a lower octane fuel could diesel.
2) my V6 example is very clear. honda engineers designed the car to run smooth, start easy and produce 270HP with the 6 fuels injectors it comes with. with those same 6 fuel injectors and pump gas, i can build a killer buick 231 V6 (forced induction), blow the doors off just about anything, but the ride will be harsh, not smooth, prone to breakdown, etc.

i see your argument, but i was trying to point out the importance of fuel ratings, etc.

lakeman

IMHO as an engineer -although not a combustion engineer-I agree that the method of producing power in a gasoline engine is to "burn" the gas, very rapidly in a controlled manner staring at the spack plug and radiating out. In a diesel, you compress the fuel and basically want it to explode - ie all fuel in the chamber ignites at the same time. (The rods and bearings in a diesel are engineered to take this, but not in a gas engine) "Pinging" which is heard when too low an octane gas is used in a gas engine, could be easily be called dieseling, as the gas pre-detonates - ie explodes. I hope I have not gone wrong here. If we have a combustion expert on the forum, please chime in.

William_B

Remember, if a salesman is telling you that, then that is what you want to hear. I would doubt the salesman has a degree in applied chemistry, or chemical engineering .

lakeman

100%
Lakeman

Scott GN231

On point (1) yes it could diesel, but I'd be very surprised to see this happen in this application-- 11:1 is a reasonably high compression ratio, but not high enough in my estimation. In theory, this is a reasonable point though.

If your point (2) boils down to something along the lines of 'engineers recommend this octane for the most enjoyable TL driving experience under a variety of driving situations', I agree. But for folks wanting to save a buck or two and not flooring it on a regular basis, I'd wager that they'd never notice the difference.

-Scott

SouthernBoy

Road Rage is correct. The fuel/air mix in your cylinders does not explode.. it burns. Rapidly to be sure, but a burn nonetheless. An explosion in a cylinder is also called "detonation". As memory serves, to qualify as an explosion, the burning of a fuel substance has to progress something like 40,000 feet per second. You do not want this to occur in your engine.

I would wager that those who believe that fuel/air explodes in an automobile engine may also believe that gunpowder in a metallic cartridge when fired in a rifle (or handgun or shotgun) explodes in the firing chamber. Not so. It, too, burns. The times when it does explode (and this does occur in handloading or with black powder firearms), the weapon is generally rendered unusable and occasionally the shooter receives injury as well.

It'a burn, gentlemen, not an explosion.

cvajs

are you sure???

a cylinder explosion does not "progress" as you say, but the pressure sure does go up. detonation is nothing more than the fuel/air mixture reaching flash point before it is scheduled to ignite.

where di you get the 40k feet per sec # ???

SouthernBoy

Yes the pressure and heat certainly do rise. All explosions "progress" even nuclear. The comsumption of the explosive fuel is the progress of which I speak. Perhaps a better choice of words may be in order.

You're right about you description of detonation as used in this context.

As for the 40,000 feet per second burn rate, that's why I said if memory serves me. I got this from a friend years ago who was deep into the gun culture (I am too, just not as knowledgable as he about come things). I would love to try to find some credible info about this myself.

We may just have to agree to disagree on this. So I'll stand by my statements regarding burn versus explosion and I suspect you'll do the same. I can live with that.

Road Rage

Yes, I am sure, or my engineering degree was based on fraudulent science, and I should be kicked out of the SAE. Also, detonation and "dieseling" are not the same things.

I have engineering studies from Honda that show the effects of using 87 octane in an NSX - it drops HP and TQ by a handful. So using it on highway driving (light load) in the TL is perfectly acceptable*. The only issue is that most gas companies do not put adequate detergents in the cheaper fuels they make, so if you use 87 a lot, use a quality injector cleaner. See "The RR Journals" for detailed info on the best fuel system cleaners.

*I assume that towing a boat or other heavy loads are not part of highway driving.

SouthernBoy

To Road Rage;

Yep, detonation is the sudden and violent explosion of unburned fuel/air mix being super compressed and heated by an expanding flame front from "normal" combustion (did I get that right?). Because of its lower octane, this fuel/air mix cannot postpone the continuing controlled burn and reacts suddenly in an out-of-control fashion. The results of severe detonation are destroyed pistons, cracked or completely damaged connecting rods, blown head gaskets, damaged valves, you name it. This is not a good thing.

wonder

SSM/Ebony is perfection. A little Zaino and it will just about bring tears to your eyes.

cvajs

ok. so then no one should chance detonation by using 87 octane fuel (most likley won't happen, but...).

cheers

cvajs

can you give brief explanation of the differences between these 2. i may be using the terms incorrectly.

Zee in NM

I believe most of you are ignoring the altitude diferences. Here in NM there are often articles about needing less octane at our altitude but cautioning to get the recommended octane below about 3500 feet. Using 91 here would be like using 94 in California. When my husband got his pickup the general manger of the repair shop told him using too high an octane caused more problems than too low an octane. The computer compensates for too low. I got 30 mpg with 87 octane on my 3000 road trip, all of it over 4500 feet.

pettydw

You want to use 91 octane min. near sea level. I found a 10% mileage reduction on 87, which did not make up for the price difference at the time. The timing is near maximum advance when cruising, though the combustion chamber pressures are lower (high vacuum - therefore less danger to engine components).

thegabrielles

Well, i am just in the mood to put my two cents in everything tonight so here you go...

I get between 18mpg (32mph average) and 29mpg (81mph average) in my AT equipped TL, I run 87 octane and yes I have a heavy foot. As most new cars, especially ours, have incredibly quick computer controls to allow for many variables including the fuel used, you can get away with lower octanes. Not saying I have do not have a slight loss in power but does 5-10hp mean that much? This is not a race car, it is sport luxory car that performs pretty well for its size. I have heard absoluely no noises from the engine nor did I expect to when I started putting in 87 octane. But also I use the quality stations to ensure I am getting the proper additives in the fuel to keep the EFI system clean. As a firefighter I can tell you gas does not burn, the fumes from it burn. This includes attomized fuel in your engine. But the "explosion " that occurs in a Internal combustion engine is a burn not an explosion. Granted, it is a quick burn. Higher octane fuels actually burn slower and thus more completely producing a higher HP figure.

Just my opinion....

dysd

I wanted to agree with Zee on this one. I live in colorado springs (elevation 6000+ ft) and for those that don't know...our "regular" here is about 2 octane points below what it usually is in the flatlands (typically it is 85). I've got my TL and I'm wondering exactly what type of gas I should put in it. I don't buy premium for my current vehicle so I don't know exactly what octane rating is usually available, but I have heard that 91 octane gas is rare here. I'm thinking 89 or 90 is most common. I'll let you know what I see if anyone is interested.

-dys

wallaceoh

Interesting note for everyone on this topic. Yes, I've read the thread and will certainly follow the advice, I found it interesting that my dealer said my new '05 had been filled with 87 octane on pickup.

The dealer rationale for the lower octane was that all cars from the dealer are supposedly filled with 87 octane. He advised that as long as the car was filled with 87 the first time and 87 was used during all subsequent fills, the car would run perfectly with no long term effects. He said that if I was ever to switch to 91 then the timings on the car would adjust appropriately and I would never be able to go back to 87 for fear of fuel injector clogging, etc.

As I mentioned, I trust the experts here, but why would the dealer advise of such?