The Real Difference Between

[eatingupblacktop]

If the day comes that I have to chose between my Grande Latte and premium fuel I'll be driving Prius FIRST...??

With a 911 sitting in the driveway, I bet not for long! B)

[bwoods]

Heck, knock out the bottle of bottled water everyday, and you break even...or those $4 coffees at your favorite shop, and wow you are really ahead....

Yup.

[Will B.]

In the most recent car & driver magazine, they also reported a decrease in MPG when using regular fuel in an Altima.

[bwoods]

My intent for my original post was to merely comment on the performance aspect of using regular vs. premium as there seems to be mixed results. I meant no reference to engine efficiency, aka gas mileage. But since it's been brought up, I haven't noticed any difference in mpg as well. Perhaps Costco gas is pretty good stuff, I don't know. At any rate, the flirt with regular was just that and I plan on tanking up on premium. The math says that if I drive 1000 miles/mo. then I'm saving only around $18/mo. on gas more or less. That isn't much for peace of mind. However, if you are now on a tight budget thanks to rising gas AND food costs (Thanks, ethanol corn industry!) $18 could mean something. After all, $18 into my wife's Matrix would be a good way to redistribute that money. It's all how you want to look at it, barring any long-term engine damage, if any.

[wwest]

My intent for my original post was to merely comment on the performance aspect of using regular vs. premium as there seems to be mixed results. I meant no reference to engine efficiency, aka gas mileage. But since it's been brought up, I haven't noticed any difference in mpg as well. Perhaps Costco gas is pretty good stuff, I don't know. At any rate, the flirt with regular was just that and I plan on tanking up on premium. The math says that if I drive 1000 miles/mo. then I'm saving only around $18/mo. on gas more or less. That isn't much for peace of mind. However, if you are now on a tight budget thanks to rising gas AND food costs (Thanks, ethanol corn industry!) $18 could mean something. After all, $18 into my wife's Matrix would be a good way to redistribute that money. It's all how you want to look at it, barring any long-term engine damage, if any.

Take a look at your LS engine's torque curve. My guess is that for the clear majority of us non-boy-racer types we spend most of our driving time with the engine operating well down on the HP or torque curve. At that point on the curve by what percentage does HP/torque differ for premium fuel vs regular...??

Virtually NONE...??

[wwest]

If the day comes that I have to chose between my Grande Latte and premium fuel I'll be driving Prius FIRST...??

With a 911 sitting in the driveway, I bet not for long! B)

The 911 is "reserved" for special days, not very many of those here in the Puget Sound area, it's a late '01 and the odo currently indicates ~20,000.

And of that 2500 was in Europe, 3,000 from east coast POE to Seattle and another 3000 from Daytona to home.

But then it does get 25 MPG cruising.

[jcrome04]

I haven't seen this thread in a while!! :D

WWEST the weather up here is sucking so bad what is going on!!!

I wish premium around here was still ~$3.30 a gallon :) Crap that was almost 6 months ago and now it's flirting with $4.70 a gallon!!!! :(

[LEXUSA]

I've been involved in many "discussions" like this one on various motorcycle forums. I know what I know from a couple of discussions with a VP RacingFuels rep years ago and personal experience. American "pump" gas and race gas should be not be considered even remotely similar. The additives in 89, 91 and 93 kill power and performance in the process of preventing knock. Race fuel continues to make power as octane increases however more octane than needed will hurt performance and efficiency.

Lower octane "pump" gas should give better mpg and make more power. Sometimes this isn't the case for unknown reasons. Maybe the ECU over-compensates to control knock and retards the timing too much. I would not think the ECU in a Lexus would be so sloppy and deliver such poor spark control as that is usually reserved for American automotive engineering. Regular 87 octane should run the cleanest as it burns the hottest. Higher octane fuel will leave more deposits due to incomplete burn if too much octane is run. Saving 10 to 20 cents per gallon should never be a reason to run lower octane.

Does anyone know what temperature the various Lexus engines run at, what temp the thermostat opens at?

[MR. LEX]

Gas that's funny I see their is still a lot of people who wants to look cute and not pay the upkeep. I had a Cadillac and Benz before the Lexus. You pay big money to buy so don't go cheap on something like gas. 91 or higher only. That's why I see some nice brand new cars riding around the city that's only about a year old ,and they sound like crap. You want to put cheap gas in a car GO BUY A FORD!!!

[AZ Mike]

Lower octane "pump" gas should give better mpg and make more power. Sometimes this isn't the case for unknown reasons. Maybe the ECU over-compensates to control knock and retards the timing too much. I would not think the ECU in a Lexus would be so sloppy and deliver such poor spark control as that is usually reserved for American automotive engineering. Regular 87 octane should run the cleanest as it burns the hottest. Higher octane fuel will leave more deposits due to incomplete burn if too much octane is run. Saving 10 to 20 cents per gallon should never be a reason to run lower octane.

"Lower octane "pump" gas should give better mpg and make more power". Perhaps I am merely a knucklehead, but everything I know about octane is that it is a measurement of resistance to "pinging" and has nothing to do with power. The LS400 does not REQUIRE, but RECOMMENDS premium fuel. I do not know all of the specifics behind the engineering of the engine, but this typically happens when the engine runs at a higher than typical compression, which would therefore increase the propensity for predetonation (i.e., pinging) with regular fuel. The engine runs at its optimum efficiency using the higher octane. You can run on regular fuel, but as mentioned, the ECU will !Removed! the timing to prevent predetonation, and in the process, runs at a less than optimum efficiency. Therefore, based on my limited knowledge, most modern cars that RECOMMEND premium fuel can run fine on regular fuel, but will likely have a small reduction in fuel efficiency due to the engine not running at its optimum (which of course proponents of regular fuel will say is offset by the cheaper price of regular fuel). I don't know that there would be any long term ill effects on the engine from using regular fuel.

[oldskewel]

... American "pump" gas and race gas should be not be considered even remotely similar. The additives in 89, 91 and 93 kill power and performance in the process of preventing knock. Race fuel continues to make power as octane increases however more octane than needed will hurt performance and efficiency.

Lower octane "pump" gas should give better mpg and make more power. Sometimes this isn't the case for unknown reasons. Maybe the ECU over-compensates to control knock and retards the timing too much. I would not think the ECU in a Lexus would be so sloppy and deliver such poor spark control as that is usually reserved for American automotive engineering. Regular 87 octane should run the cleanest as it burns the hottest. Higher octane fuel will leave more deposits due to incomplete burn if too much octane is run. ...

I looked into things several years ago, and the above is pretty much the exact conclusion I came to as well.

So, when friends ask me for advice on this (as they often do after they've bought a new car and want to do what's best for it), I tell them that if the manual says their car works with 87, they might be doing worse with 91, even without considering cost.

Lexus LS400 of course may be different. So far, I just put in 91 in my '91 (not just because it's got a ring to it), since that is recommended, and I have not yet been convinced the engine management can handle 87 without problems, but for example ...

for my 1985 911, it requires 91 (92 actually, but can't get it), and being just old enough, the engine management can't accommodate lower octane. So if I drive aggressively with 87 in there I could damage the engine. In this case there is no option - I use 91. Once I filled up with 87 by mistake. I drove like an old lady for half a tank to protect the engine, then filled with 91. I noticed my mileage increased by about 5% for that half tank, but it's hard to tell if it was the low octane or the granny driving style that did it. To tell for sure, I'd have to drive granny style on 91, and I'm just not willing to do that. B)

for my wife's minivan, it says it will get 210 HP running on 91, 205 HP running on 87. Clearly 87 is OK, so we use that, giving up 5 HP for all the other benefits.

To potentially launch on another tangent, I never ever (now that I know) use ethanol. If nothing else, it has about 2/3 the energy content of gasoline, so if the fuel is 15% ethanol, it's like getting fuel with 95% (85 + 15*2/3) of the energy in gasoline ==> 5% loss in mpg. There are engine-life issues/doubts beyond mpg. If the fuel has ethanol in it, there will be a sticker on the pump saying so.

Ed

[Marklouis]

... American "pump" gas and race gas should be not be considered even remotely similar. The additives in 89, 91 and 93 kill power and performance in the process of preventing knock. Race fuel continues to make power as octane increases however more octane than needed will hurt performance and efficiency.

Lower octane "pump" gas should give better mpg and make more power. Sometimes this isn't the case for unknown reasons. Maybe the ECU over-compensates to control knock and retards the timing too much. I would not think the ECU in a Lexus would be so sloppy and deliver such poor spark control as that is usually reserved for American automotive engineering. Regular 87 octane should run the cleanest as it burns the hottest. Higher octane fuel will leave more deposits due to incomplete burn if too much octane is run. ...

I looked into things several years ago, and the above is pretty much the exact conclusion I came to as well.

So, when friends ask me for advice on this (as they often do after they've bought a new car and want to do what's best for it), I tell them that if the manual says their car works with 87, they might be doing worse with 91, even without considering cost.

Lexus LS400 of course may be different. So far, I just put in 91 in my '91 (not just because it's got a ring to it), since that is recommended, and I have not yet been convinced the engine management can handle 87 without problems, but for example ...

for my 1985 911, it requires 91 (92 actually, but can't get it), and being just old enough, the engine management can't accommodate lower octane. So if I drive aggressively with 87 in there I could damage the engine. In this case there is no option - I use 91. Once I filled up with 87 by mistake. I drove like an old lady for half a tank to protect the engine, then filled with 91. I noticed my mileage increased by about 5% for that half tank, but it's hard to tell if it was the low octane or the granny driving style that did it. To tell for sure, I'd have to drive granny style on 91, and I'm just not willing to do that. B)

for my wife's minivan, it says it will get 210 HP running on 91, 205 HP running on 87. Clearly 87 is OK, so we use that, giving up 5 HP for all the other benefits.

To potentially launch on another tangent, I never ever (now that I know) use ethanol. If nothing else, it has about 2/3 the energy content of gasoline, so if the fuel is 15% ethanol, it's like getting fuel with 95% (85 + 15*2/3) of the energy in gasoline ==> 5% loss in mpg. There are engine-life issues/doubts beyond mpg. If the fuel has ethanol in it, there will be a sticker on the pump saying so.

Ed

ethanol, hate the stuff...wish i knew who didnt add it to thier fuel. my gas mileage has dropped 7% since that's all i can find here in north alabama, the ethanol capitol, and who knows what it's doing to my internals in the engine.

[oldskewel]

"Lower octane "pump" gas should give better mpg and make more power". Perhaps I am merely a knucklehead, but everything I know about octane is that it is a measurement of resistance to "pinging" and has nothing to do with power. The LS400 does not REQUIRE, but RECOMMENDS premium fuel. I do not know all of the specifics behind the engineering of the engine, but this typically happens when the engine runs at a higher than typical compression, which would therefore increase the propensity for predetonation (i.e., pinging) with regular fuel. The engine runs at its optimum efficiency using the higher octane. You can run on regular fuel, but as mentioned, the ECU will !Removed! the timing to prevent predetonation, and in the process, runs at a less than optimum efficiency. Therefore, based on my limited knowledge, most modern cars that RECOMMEND premium fuel can run fine on regular fuel, but will likely have a small reduction in fuel efficiency due to the engine not running at its optimum (which of course proponents of regular fuel will say is offset by the cheaper price of regular fuel). I don't know that there would be any long term ill effects on the engine from using regular fuel.

The above fits with my understanding as well, except maybe not 100% with "The engine runs at its optimum efficiency using the higher octane."

If the engine is designed to run on 87 (which the designers would do to provide all the benefits of lower octane gas, sacrificing pre-detonation resistance, resulting in an engine with less peak power), it can run at optimum efficiency on 87. If it were to run with 91, there is still no risk of pre-detonation, but the fuel components that inhibit predetonation (by reducing the combustibility of the fuel) mean the fuel does not burn with the same speed and energy of 87. ==> higher fuel cost in exchange for lower mpg and no increase in power.

I think there's a difference between how a Ferrari would respond to 87, vs. a Honda minivan. The Ferrari engine would be designed to provide max power per displacement (, weight, etc.), with a very careful _mechanical_ design and engine management to match. Surely it would require high octane, and dropping down to 87 would cause the engine management system to move far away from the tuned operating point that the engine designers crafted. It would protect the engine, but in addition to a drop in peak HP, mpg would probably drop, and it might not perform smoothly, etc. Ferrari could of course design an engine that would perform acceptably well with 87, but to do so would compromise the high peak they strive for, and their customers don't want that. Same reason they don't have rear seats or a trailer hitch.

The Honda engine (like the 3.5l V-Tec we have) understandably seems to be designed more for flexibility than for high end output. E.g., one cool feature is that it will shut off one of the two intake valves in each cylinder at low engine loads (idling, or cruising). With only one intake valve open, the fuel-air comes in faster, creating better mixing and more complete combustion ==> better mpg and lower emissions. Variable valve timing as well. In this car, it recommends 91, but gives a spec for 87 with a reduction in peak power of 5 HP. I expect that since this engine has such flexibility in the mechanical design, the engine management (injection, timing) can handle the 87 far better than the Ferrari could. Ours seats 7 and has a trailer hitch.

I expect the LS400 is in between these examples, which is why this is an issue. I bet there's not much discussion about what octane to use on the Ferrari message boards. ;) I bet the hot issue right now is how to get their money out of their hedge funds that just closed up.

[MR. LEX]

oldskewel I agree with you. How can you lost Hp and gain mpg. And everybody else who says 87 fuel gives you more power and better mpg. Then why Race cars are running 100+ OCT. instead of 87. Why lambos call for 91 or higher fuel. Or any other true sports car at that. Calls for 91 or higher. Everybody best bet is to see what type of fuel your car calls for 87,89,or 91 and Stick with it.

[SKperformance]

Who really cares anymore !

Gas is so cheap . I feel like a teenager in the 90's again where $20 bucks will actually get me somewhere.

[jcrome04]

Hahaha so true B)

[don corleone]

yeah gas prices are great now. cant convince everyone but i only use 91+. a friend of mine used 89 in his 1990 cutlass purchased off the lot brand new and had to buy new injectors because the old ones were clogged from the lower octane fuel. also if you go to jiffylube.com and click on how cars work and see the pistons and rods it shows what happens when using lower octane fuel

Go Obama!

[SRK]

Lower octane fuel does not clog injectors. Contaminated fuel, old fuel, old fuel filter, and most of all the fact that they were Rochester injectors, is why they clog.

Christ, next up will be low octane fuels cause bad breath and high octane fuel make sunsets redder.....

[don corleone]

Well hey maybe GM cars are the POS that i thought they were. thanks for clearing that up!

[SRK]

You're right, they are.

[jcrome04]

yeah gas prices are great now. cant convince everyone but i only use 91+. a friend of mine used 89 in his 1990 cutlass purchased off the lot brand new and had to buy new injectors because the old ones were clogged from the lower octane fuel. also if you go to jiffylube.com and click on how cars work and see the pistons and rods it shows what happens when using lower octane fuel

Go Obama!

You only need to use what octane is required in the owner's manual. There is no sense in running Premium in a vehicle that requires regular.

Jiffy lube sucks. Period. There's no more to that conversation.

Go Obama? Let's stay on topic please. If you want to talk about Obama find the Obama thread in General Discussions.

Why did this thread get revived anyways? I started it when I was like 12 :lol:

[don corleone]

I was saying go obama because since the election the gas price fell and that was what sk was saying that since the price dropped who cares.

[jcrome04]

Then state that's why you made that comment.

But it really has nothing to do with Obama personally either....

Gas prices have always gone up during an election (never to this extent) and dropped after the election. Also send most of your thanks to the speculators. If you'd like to know grossly more info on this topic.. You can also find the Gas Prices thread, in the General Discussion forum. ;)

[don corleone]

yeah sorry for hijacking the thread. gas is strange though. i always noticed that premium Lasts longer even in cars not designed for premium. does it improve performance, i think so too. i read import tuner, SCC etc. and on the power pages when they dyno cars with bolt-on parts they list fuel octane along with outside temp etc. octane is fuel's ability to resist knock, right. and knock is also known as pre-detonation where the gas spontaneously combusts and can throw piston timing off. and high compression engines require high octane fuel, so a low compression engine should be able to use less fuel to get the same amount of compression. is this correct, shouldn't the ecu be able to tweak the air/fuel ratio for optimum performance with gas that can withstand more pressure? even though an engine uses x amount of air adding more air faster via a larger intake increases power and maybe mpg so upgrading fuel via octane should do the same.

just thoughts based on my knowledge of engines.

[SRK]

Don Corleone, wit' respect, you could, y'know, study some technical type manuals, and uh, do some research rather than listen to dem little tuner guys what know nuttin' about nuttin. I'm sure you's is like keen and everyting on cars an' stuff, but a solid, you know, foundation of theoretical knowledge is da key to da kingdom. Then like you's will know what pistons and compression is all about eh? You could be a real wise guy.

But I say all dis' wit' da most respect. I mean like ownin' a Lexus makes ya one a da crew aroun' here. Which is good.