[warubozu]

As stated in a few posts earlier, high octane gas doesn't mean that your engine will run better or make more horsepower if you do decide to run it. Higher octane gas means that the gas was made to resist detonation in higher compression engines. Higher octane gas can also help in older cars with higher mileage on their engines especially if compression ratio has been slightly boosted higher due to carbon deposits within the compression chamber of the engine.

If you can run a lower grade of gas without your engine knocking or running rough it won't do any harm to do so. You won't loose any performance in running lower grade gas unless you notice your engine starts to knock during acceleration. I currently run racing gas in my race car (125 octane) but that's only because I have very high compression within my engine and it won't live if I feed it anything less.

 

[Elec]

Just wanted to point out that, while it hurts when actually at the pump looking at the numbers, it's not really all that much more expensive to run premium than regular.

Suppose you get 20mpg, which is a fairly low average. Now suppose you drive 20,000 miles a year, which is somewhat higher than average. Simple math shows you'll burn 1000 gallons of gas a year. Right now at my local gas station, I think premium is 25 cents a gallon more than regular. So more simple math, and your extra cost is a lousy 250 bucks. If you get better mileage than that or drive fewer miles a year, the difference is even less.

Unless you're at the point where you can barely afford to put gas in your car anyway (which I assume isn't true if you're buying a different car), I wouldn't even sweat having to buy premium.

 

[Teerawit]

Quote:

Originally Posted by bobeau Still don't agree with your thinking here. The isoctane mixture is a _reference_ to base on octane rating off of, the octane rating itself does not speak to an actual fuel's composition. It really comes down to optimizing the nature of the fuel burn in your engine... if you run too close to the ragged edge you can get knock, further away from this edge you lose combustion efficiency. Once again, words like quality do not factor in the same sentence as octane. In fact one could make the opposite argument to some nasty very high octane fuels (such as xylene) which have rough burn, are heavily polluting, hard on seals, etc. There are many ways you can achieve an octane rating.

My reasoning is that the octane rating speaks of the quality of the molecules present in the gasoline mixture. Some molecules are better than others, hence giving more knock resistance. That's why i said

The point is the same. You want a higher composition of a certain molecule in your gasoline because this molecule resists knocking, while other molecules will "contaminate" the gasoline and make it more prone to knocking.

I didn't say that molecule has to be isooctane. The octane rating does emphasize the quality of the fuel based on its overall composition in relation to knock resistance.

 

[nikongod]

Quote:

Originally Posted by Elec Just wanted to point out that, while it hurts when actually at the pump looking at the numbers, it's not really all that much more expensive to run premium than regular.

about $2.50 a week extra is worth the 3psi higher i can run my turbo at above regular

its only like 30HP diference. nothing spectacular

 

[bg4533]

The importance of high octane fuel will depend on the specific car and engine. I suggest you try to find a Lexus forum and ask there.

 

[bobeau]

Quote:

Originally Posted by Teerawit My reasoning is that the octane rating speaks of the quality of the molecules present in the gasoline mixture. Some molecules are better than others, hence giving more knock resistance. .

Again, octane rating mostly speaks to the nature of a fuel burn, and can be both beneficial or a hindrance based on the conditions the fuel is used in. Let's please throw all notions of "quality" out the window.

 

[grawk]

Of course, there's no guarantee you'll get low octane gas when you buy the cheaper stuff...it's a minimum, not a guaranteed rating. I know that stations have on occassion had the same gas in all 3 tanks...

 

[Sovkiller]

Quote:

Originally Posted by MrJoshua In the UK, our Super Unleaded and Optimax is from 97-99 RON (Octane). Our standard stuff is from 93-95 RON. Anyway, higher octane is usually higher quality (more additives to help clean the engine etc, better filtration etc). You can also advance the ignition timing when running higher RON fuel, therefore increasing performance. Some ECU's do this automatically, some when tuned. Many tuned Japanese import cars will not run on anything lower than 100 RON!! I realise in the US the means of calculating the RON is different to the UK/EU (you guys use RMS values), so our RON's can't be compared (apparently). HTH?

I was reading about that, some time ago worried about the increases of the gas price and imposobility of getting decent prices in premium gas around here, and it is all the opposite, the high octane gas has less aditives and detergents, to avoid the explossions during the compression in the small chambers of the high performance vehicles, many of the regular cars we see on the streets perform much better with regular gas...87 octane...

From consumersreport.org:

".....Paying for premium gas can be a waste of money

Many people use premium gasoline in the belief that it's better for engines than regular. That can be a costly mistake, especially during times of high fuel prices. Octane grades don't represent a “good, better, best” choice; they simply measure the resistance of fuel to knocking or pinging, a condition in which gasoline burns uncontrollably in the engine's combustion chambers. Knocking and pinging can damage an engine.

While high-octane formulations resist knocking better than lower octanes, most engines are designed to take regular gas, which has an octane rating of about 87. Engines requiring premium gas are typically the more powerful ones found in sports and luxury vehicles. Those engines use a very high compression ratio, making them more vulnerable to knocking, so recommended fuels have octane ratings of 91 or higher. Using premium gas in an engine designed to run on regular doesn't improve performance.

Some engines for which premium gasoline is recommended can run on regular without problems. That's because the engine's knock-sensor system detects the presence of uncontrolled burning in the chambers. When it does, the engine's computer-control system retards engine timing, eliminating the knock but slightly reducing power. If you don't mind giving up some performance, you can run these engines on less-expensive regular gasoline. To check whether your engine is capable of running on regular gas, read your owner's manual or ask your dealership's service department.

A hot-running engine or one with deposits may also knock, but premium gas may still not be the best solution. Service a hot-running engine as soon as possible, and handle deposit buildup with treatments that dissolve them. The treatments may be less expensive than regularly using premium gas...."

So now you know the truth....

 

[aerius]

Given that the Lexus SUV engine has a compression ratio of 10.5:1 to 10.8:1 depending on the model year, premium gas is a good idea. As a general rule, once the compression ratio gets above 10-10.5:1, you can't get away with using 87 octane gas unless you drive lightly & smoothly in relatively cool weather. If you live somewhere cool and never put the gas pedal more than halfway to the floor, you can get away with 87 octane gas, otherwise, move up to the 89-91 mid-grade.

 

[neil]

A friend of mine that owns gas stations told me that their distributor only has two types of gasoline in his fuel truck.. the lower octane, and the higher octane, and that the mid-grade is just a mixture of the two -- how scientific the measurement of the ratio/mixture, he wasn't sure.. in fact, he said that if you're going to go with anything, avoid the mid-grade and go with the highest octane available at the station.. but overall, as my dad recommends, if the manual says 87, by all means, use 87. That's how the engine was designed and tested.

 

[loveheadphones]

Gasoline is actually quite a complex product. Refiners take in crude oil and transform it into Jet fuel, Diesel, and Gasoline (ratios made depend upon market conditions) as their major saleable products.
Gasoline is blended from at least 10 different components tanked in the refinery. Indeed, iso octane is sometimes used in order to upgrade the octane of the blend, but sparingly since it is so expensive.
All gasoline used in a state must have the same specifications (vapor pressure, octane, sulfur content, aromatic content, etc.) set by the EPA or local organizations (AQMD, etc.). So basically all gasoline (with the same octane) is the same, except for the detergent additives.
Only two types of gasoline are shipped from a (American) refinery: 87 octane and 91 octane. Octane in the U.S. is determined by (RON+MON)/2. The choice on producing either 91 or 87 is, once again, determined by market conditions.
I don't know anything about additives because most of those are added at th e terminals.
Almost all the inputs and outputs of a refinery in the U.S. are traded on the NYMEX or CBOE, so they are quite transparant.

 

[Sovkiller]

Quote:

Originally Posted by neil A friend of mine that owns gas stations told me that their distributor only has two types of gasoline in his fuel truck.. the lower octane, and the higher octane, and that the mid-grade is just a mixture of the two -- how scientific the measurement of the ratio/mixture, he wasn't sure.. in fact, he said that if you're going to go with anything, avoid the mid-grade and go with the highest octane available at the station.. but overall, as my dad recommends, if the manual says 87, by all means, use 87. That's how the engine was designed and tested.

Well not sure what type of gas station it was, but I used to work/administrate an Amoco gas station for over 2 years, and all the gas trucks that visit us to deliver gas, had the three compartments on them, one of each type of gas, so it is not an illusion, the three octanes exist....

Even more, one of the times while I was pumping 89 gas, I noticed that the gas was pinkish in color, I told with the owner, and he told me not to make any comments, that they seemed to "had made a mistake" and filled in the 89 tank with Citgo gas instead of Amoco (one of the few that still has colorants).......so now you know, be careful, with the brands of gas, they are indeed a big joke, the owners of the gas stations, usually had some kind of arrangments with the truck drivers, and it is all a big fraud, they use to pump the cheapest avaialble....now I remember some suspicious envelopes that I had to give to those drivers while delivering......

 

[Stephonovich]

About the using the knock sensor to use cheaper fuel... not a good idea. Yes, it will work, but it's not good on your engine. It's there for idiot proofing. Older cars didn't have them, so knocking/pinging/predetonation (many terms for the same thing) would occur.

Our '97 Dodge Intrepid R/T needs 89 octane minimum, due to it's slightly higher compression (9.9:1) ratio than most. Not a huge jump; in fact, a few of the stations are here have 89/90 octane as their low-grade, so no big deal.

 

[utep10]

Thanks for all the replies.

I've found a Lexus forum and have started to puruse it.

The example of annual added cost of using premium gas kind of puts it into perspective for me.

We are going to look at the 2004 Lexus LX470 on Sunday. If we decide to get it, I think the premium stuff is going in as of now. From what I have read here, it sounds like it is POSSIBLE to harm the engine with lower octane gas plus I'm not really interested in hearing our new vehicle pinging down the road.

I'll let you know what we decide.

 

[Orpheus]

Quote:

Originally Posted by utep10 My wife and I are thinking of purchasing a used Lexus SUV and the manufacturer recommends using high octane gas (I think 92 octane). Is this recommendation based on getting maximum performance only or does it also help in some way of keeping the engine in top condition. Will using lower octane gas harm the engine in anyway or do we only lose performance?

bottom line:

1. if you use lower octane gas, you'll lose some power/efficiency and thus gas mileage. how that would translate into cost/mile i do not know.
2. but no, it should not harm your car: modern cars have knock sensors and that sort of stuff. it will automatically retard your car to safe levels. especially advanced cars like the lexus. besides, you can't even get 92 octane around here in california.
3. putting higher octane gas than the recommended number should not give you any extra performance.

the '05 corvette uses 93 octane gas. and there is no such thing in california.

that said............ science aside, i personally would never put lower grade gas into my own personal cars. no matter the cost. but if you think about it, at today's prices, it doesn't make any sense to go to a lower grade gas. i mean, if it costs $2.80 for 87 (is that the lowest number?) octane cheap-o gas, and $3.00 for 91 octane top-of-the-line.... well, that's less than a 10% difference, and after pumping a full tank, you only saved $3 on $45 worth of gas. (note that $3 out of your $30,000 car is 1/10,000 of its cost.) doesn't make any sense at all.

...........................so, the bottom line of the bottom line?--just pump what your frickin manual tells you to.

EDIT: as someone pointed out earlier, altitude and temperature also affects what octane you need... and quite significantly. unfortunately i don't remember which way it goes--but you can search online. the 92 octane rating your car has is for a specific altitude and temperature. as for another post about knock sensors being "idiot proofs"... i disagree. as i stated, the '05 corvette is supposed to use 93 octane gas. good luck finding that crap around here. and i don't see no 2005 vettes farting down the highway.