Regular Or Premium Unleaded Fuel?

[bartkat]

Premium gas here is either 93 or 94 octane. I've noted that when I am traveling and have only the choice of 91 octane, the car doesn't have as much pep. It doesn't knock, but seems a little down on power.

Some areas also have the reformulated (oxygenated?) gas. The car doesn't like it as well either.

[SW03ES]

Im sure most of us are familiar with SUNOCO gas station, has anyone noticed a difference by using their ULTRA 94 gas, with octane level 94

No, there've never been any studies published by Sunoco about the benefits of their 94 octane gasoline over traditional premium (91 or 93). I've spoken with several mechanics, and they say its just a waste of money.

[Regan]

My local paper, the Vancouver Sun, did an article just last week on what a waste of money premium gas is. Supercharged and turbocharged cars are the exception, as they can have detonation.

The experts they contacted say that the amount of horsepower even a Porsche makes with premium gas over regular is not noticable

to the driver. Only a timing device would register the extra power,

so they say.

Years ago a high horse power engine had to have premium, as there

were not any knock sensors. Everybody's engine rattled now and then.

Hey, do you know what that pinging is?

It's the sound of the cylinder walls vibrating like a bell! ....Ouch.

Real detonation is not the same as pinging, and can destroy an engine. Modern knock sensors keep that from happening.

I like to fill up with premium when I go on a highway trip into the Rockies. With lots of passing on mountains, I like the extra insurance of having premium. The rest of the time regular works ok, and the experts agree.

Regan.

[ROSS]

THANKS TO ALL! YOU HAVE CONFRIMED WHAT I

THOUGHT. I WILL BE USING PREMIUM FUEL.

[ToddLS400]

Use premo ONLY in your car. Regular gas creates a lot of carbon buildup as well. Regular gas gives you less gas mileage than premo and I have a noticable less amount of power. I step on it a lot and I do notice the difference in gas. The increased gas mileage with premo just about washes out the extra money spent. Plus your engine runs better and cleaner.

The worst regular gas is Arco. That gas is ghetto fuel. When I see people with nice cars filling up at Arco I just laugh. What are they thinking? They paid all of this money for a nice car and they fill up with that watered down Arco gas.

[SW03ES]

I've never even heard of Arco lol. Here we have "Lowest Price" as our ghetto gas.

[VMF]

got some preimium gas once from some ghetto delta gas station, oh man i regret it! i did only 250 miles on a highway plus my car was stuttering and resisting acceleration all the time. yeah use the gas that is recommended by your manufacturer. its safer this way. and you can save some money because you will not have those "out of nowhere" malfunctions which might appear if you use the cheap gas. the temperature during combustion for the high octane is bigger then on a regular gas. so it gives more pressure. what the octane digit means is a percentage of gases mixed.

[Lexusing]

Read this clip from USAToday...

http://www.usatoday.com/money/autos/2003-0...remiumgas_x.htm

Hope this will help clear up some....

[bbsal]

I agree with all the posts, I would do what the manual says (min 91 octane) and not listen to what others have done.

Im sure most of us are familiar with SUNOCO gas station, has anyone noticed a difference by using their ULTRA 94 gas, with octane level 94,

rather than any other gas with a max octane of 91 ???

no studys but my car just feels better with 94.thats all i use in it because thats what the car likes.some say its a waist of money but think about your timing being retarded and carbon builup and lower gas milage!that alone makes me stay with ultra.

i mean think about it.some of you that ask these questions have 60,000 dollar cars and others have 30,000 dollar cars so why risk it over 30 or 40 dollars per year???stick with the manual of your car or just use high test!

[SW03ES]

Well actually, if the ECU is designed to run on regular, and you run premium you're causing as many problems as if its designed to run premium and you run regular. The timing and combustion is set for one grade of gasoline, use what it says to use, no more, no less. High test in a regular motor causes pinging, carbon deposits, and robbed fuel mileage too.

Thats part of what I've been saying about the 94, its above what the car is designed to use, so anything else just gets burned off and wasted.

[VMF]

if you use higher ocane then recommended your seals will get burned as well due to higher combustion temepratures. it means blue smoke and $$ to waste :D

[SW03ES]

See?

Preach it my brother! :snoooorrrtttt:

[bartkat]

I'm not going to buy into those "harm" arguments against using normal premium fuel. The higher octane will fool the knock sensor and the ECU will then allow more ignition timing advance, thus a slight improvement in performance. Using premium pump gas certainly isn't going to cause piniging. If anything, regular gas is going to be on the edge of pinging or pre-ignition knock under high heat and high load conditions. The fuel spec calling for 91 octane simply means that's the minimum octane. The car is set up to run on that because, like in Califorina, 91 octane is the maximum available. However, in many place you have the choice of 87, 89, and 93 (or 94) octane gas. With that range of choices, the premium 93 or 94 is the only way to go.

Running premium won't pay back in cost via much increased gas mileage, but it's not going to hurt your engine.

Sure, you could hurt an engine by running avgas or race gas, but we don't usually see that at the pumps.

[SW03ES]

Sure, 93 is the best bet, thats what we have here. I have always been told, by multiple sources though that running premium fuel when the manual calls for regular speeds up carbon deposits, worsens fuel economy etc.

[bartkat]

Before cars had catalytic converters and knock sensors and such, but leaded gas became unavailable, cars used to knock terribly on regular gas. But that was many years ago. The transition to emissions controls and unleaded gas was pretty rough for 2 or 3 years there.

[SRK]

Using gasoline of a higher octane rating than required will NOT cause any problems - at all. Higher octance fuels burn more slowly than those of lower octance, and with greater resistance to pre-ignition under high pressures. The only harm will be to your pocketbook - spending more money than is needed.

Most modern engines have PCM's that will advance ignition timing until they detect knock (pre-ignition) and then stabilize timing at that level. Many PCM's record the knock count as they continue to probe for the most timing advance possible. This is a normal attribute of many PCM programs. The lower the octane, the later the ignition timing will occur, and that will cause a reduction in power. The power ratings advertised for our engines are determined at particular octane and air temperatures (standardized tests) and if you use a lower octane fuel the power output will be lower, just like if the air temp is higher, or the altitude is higher (Denver CO).

Using any leaded fuel (avgas or racing blends) will contaminate the O2 sensors, leaving them quite useless. This will produce a code from the PCM and cost you big time replacing them. Also the catalytic convertors will be irreversibly damaged, costing more money.

Use the octane recommended by the manufacturer. I use nothing lower than 91.

[SW03ES]

Sounds totally reasonable to me, I just go by what I've been told over the years.

[VMF]

gen I and II cars have distributor and timing belt, they dont have those PCM programs unoftunately. on 1UZFE its all done in old facion way

[oversteer]

OK...more of my .02. Remember that Octane allows for higher compression before self ignition. The more compression a motor has, the higher the temperature in the cylinder gets during the compression stroke (PV=NRT). With low octance gas, the temp could get to the ignition point before the spark starts the explosion which causes a knock. Just one thing though.....

The LS400 motor is a 4.0 liter V8 that only puts out 255HP. Considering that there are 2.2l 4 cylinders delivering this kind of power, it shows you exactly how low the compression/stress is on the motor. Thats why they last so long.

More importantly, the chance of detonation with low octane only occurs when the engine is under max load. This means you have your foot to the floor and are planning on getting somewhere fast.

The compression on the LS400 is very low and I rarely if ever have my foot on the floor. I use 89 around town and 87 on long hwy trips. Never had a knock. Anyone who tells you that they get better mileage, a cleaner engine or more power from high octance, doesn't understand what octane is and what it means. As an FYI, I use BP/Amoco gas in all of my cars.

Chet

[bartkat]

You car doesn't knock on regular gas because it has the ability to !Removed! (or not advance) the ignition timing prior to reaching a knock condition. I suppose that's all well and good if you are willing to sacrifice some performance. If your engine calls for regular gas, that's all well and good. However, if it calls for premium, sooner or later you could have problems.

[oversteer]

My engine doesn't knock because I don't go full throttle. 175K miles and going.....

Also, a knock sensor works by detecting the vibrations produced by a knock and keeping the timing retarded to compensate. A knock sensor is reactive not proactive so it doesn't prevent a knock from occuring. It senses that knocks have occured and compensates accordingly.

I have several track only race cars and several performance street cars. I use 91-103 octane in all of them. Based on my driving style, I think higher octane is a waste in my Lexus. YMMV.'

Chet

[spiller91ls]

wow, your consider 10.5:1 compression as low, what planet are you from. you need to pull your spark plugs and make sure your not getting little silver specks on them. If you are, then those little specks are part of your pistons, as far as only worring about detenation at full trottle you are just fooling yourself, it can happen going up hill at partial trottle.

[bartkat]

From another forum.

Here's an eye witness report on the result of running regular gas in a Lexus that requires premium fuel:

"I just came from hanging out at the lexus dealer behind the scenes so to speak. I just got a look at a brand new crusty black carbon covered SC430 motor that got swapped out for a new one. Mechanic told me that the guy put 89 octane in it and ran it. THIS THING had thick filthy black carbon build up all over the pistons. He says that when carbon builds up the heat doesn't transfer away quick enough and it burns the rings and stuff..

Is anyone running low octane gas and has anyone heard of or had any issues like this with their IS300 or other lexus?. I run lo-octane occasionally and can't tell a difference except it kind of pings when you hit the gas but immediately goes away..

I had no idea that it builds crap up on your motor like that!!.. I could take a pic tommorow if you all want to see it?"

[tds]

Hello all,

I have a 1991 RX300, and shortly after I bought it, I asked Lexus for some detailed explanations on horsepower vs octane. I think you will find their answer interesting.

Here is my question:

I have one more question I would like to ask about a fuel issue with my RX300 that is unclear.

The owners manual states that the Octane rating should be 87 or higher.

It says that for improved performance, the use of premium unleaded gasoline with an Octane rating of 91 or higher is recommeded (page 264 in the owners manual).

The sales brochure says that the engine is rated at 220 hp. Is this 220 hp rating with the 87 octane fuel or with the 91 octane fuel? If the rating is 220 hp with the 87 octane fuel, what is the rating with 91 or 94 octane fuel (again, in the manual it says that for improved performance, the use of premium unleaded gasoline with an Octane rating of 91 or higher is recommeded). Is the engine detuned to run on the 87 octane and the timing advanced automatically to run on 91 or 94 octane? I would appreciate it

if someone could provide a detailed comprehensive technical explanation.

Here is Lexus's answer:

Our Technical Group has provided the following information in reply to your question:

There is more than one "octane rating". Research Octane Number (RON) is a laboratory rating that manufacturers generally use.

Motor Octane Number (MON) is another laboratory method of measurement.

Anti Knock Index (AKI) is the number quoted at gas stations. It is an average of these two: RON + MON / 2

87AKI is equal to 91RON. The engine in the RX300 produces 220 hp on this "regular" fuel. If premium fuel is used (over 87AKI or 91RON), a slight improvement in power output is likely.

The ignition system used on the RX300 continually monitors engine knock (detonation), and tailors spark advance to operate at where its peak performance can be obtained. Hence, the better the fuel, the better the

potential performance (within limits, of course).

We hope this information will be useful.

Summary: I use Sunoco 94 Octane all the time. This fuel us cleaner that the lower octane fuels and provides me with more hp. I tried the regular 87 octane fuel and then immediately after the 94 octane and there is a significant increase in power (i.e. the RX seems a lot more 'peppy', almost like it has had a tune up). I estimate that I am getting around 10 more hp (i.e. around 4.5 %) when using the 94 octane, and I certainly can feel the difference. A cleaner engine with the 94 octane is just a bonus.

[wolver1ne516]

Whatever you do please do not use anything less than 91 octain.

reason being is higher octain detonated much later than low octain. and an engine designed for high octain runs more eficient on just that, higher octain fuel.

lower octain has more impurities therfore more burning capabilities and a earlier detonation point. higher octain engines have a later detonation point of combustion rating hence a higher compression point of detionation.

using a lower octain will not only cause pinging, but unwanted, early engine power robbing, detonations. [PHEW]