switching from 87 octane to 89 octane gas (IS250)
05-31-12, 09:02 PM
#16
Pole Position
Join Date: Aug 2011
Location: IL
Posts: 383
Likes: 0
Received 0 Likes
on
0 Posts
I have a similar thread comparing mpg on 93 and 89 octane: https://www.clublexus.com/forums/is-...ctane-gas.html
I got similar replies, but most of the negative ones didn't really have much scientific backing.
My belief is still that running lower octane is okay and there is no difference in mileage as long as the engine does not knock. Whether it knocks depends not only on the design/tuning of the engine at the recommended octane, but also on how you drive it and the conditions such as temperature and atmospheric pressure, and many other factors. Because of these variables, some people can get away with running 87 octane under restricted conditions, while other people can't.
If you accelerate hard such as in city traffic, or desire maximum power from your engine, you may get knocking on anything less than 91 octane. You need to be careful because you may not know that the engine is knocking. There is a knock sensor that will retard ignition and prevent further knocking, but only after knocking has already occurred. Only when it is really severe will it trigger the check engine light. Also, when the ignition is retarded, the engine produces less power, so you may compensate by pushing the gas pedal harder and your mileage will be worse.
So if you don't want to worry about everything I just said, or risk it, just run 91 or higher octane.
I got similar replies, but most of the negative ones didn't really have much scientific backing.
My belief is still that running lower octane is okay and there is no difference in mileage as long as the engine does not knock. Whether it knocks depends not only on the design/tuning of the engine at the recommended octane, but also on how you drive it and the conditions such as temperature and atmospheric pressure, and many other factors. Because of these variables, some people can get away with running 87 octane under restricted conditions, while other people can't.
If you accelerate hard such as in city traffic, or desire maximum power from your engine, you may get knocking on anything less than 91 octane. You need to be careful because you may not know that the engine is knocking. There is a knock sensor that will retard ignition and prevent further knocking, but only after knocking has already occurred. Only when it is really severe will it trigger the check engine light. Also, when the ignition is retarded, the engine produces less power, so you may compensate by pushing the gas pedal harder and your mileage will be worse.
So if you don't want to worry about everything I just said, or risk it, just run 91 or higher octane.
people who actually MAKE these cars say premium gas only.
06-01-12, 05:58 AM
#21
Speaking of lack of science... quote from the other thread-
Were you actually plugged into the OBD port and datalogging?
Because the knock sensors are good enough you probably wouldn't notice them triggering if you were taking it easy, but that doesn't mean they weren't.
For those in the US confused by this- 98 in Australia is roughly 93.5 octane in the US... .they use a different rating system.
Originally Posted by Toymota
I haven't noticed any knocking.
Because the knock sensors are good enough you probably wouldn't notice them triggering if you were taking it easy, but that doesn't mean they weren't.
For those in the US confused by this- 98 in Australia is roughly 93.5 octane in the US... .they use a different rating system.
06-01-12, 09:24 AM
#22
Wow!!!! These "scientists" think they are smarter than the engineers who designed this car. I guess the "scientists" are smarter than the same engineer that designed these cars to run on Premium. ::eyeroll
In the end, it's not my car, so if you want to run 87 octane to death of the car.... it's your call.
Using the same scientists' logic here, it's safe to run 87 octane on a Porsche, Ferrari and Lamborghini... might well dump 87 octane fuel into F1 cars too then drive it slow.
In the end, it's not my car, so if you want to run 87 octane to death of the car.... it's your call.
Using the same scientists' logic here, it's safe to run 87 octane on a Porsche, Ferrari and Lamborghini... might well dump 87 octane fuel into F1 cars too then drive it slow.
06-01-12, 09:29 AM
#23
It's like the extended oil change interval debate. One side could just say "the manufacturer specifies 5,000 miles so that's what you should do, no ifs, ands or buts!". No science, no progress, no intelligent discussion and probably a bit of name calling thrown in for good measure. While the other side could say: we know what we're doing, we use top quality synthetic oil, and we have used oil analyses to show that the oil is still good. That is the sort of scientific discussion I would like to see.
06-01-12, 11:02 AM
#24
The engine in your car is designed to run on a certain octane rating gasoline.
The ONLY thing that Octane rating measures is the resistance of the fuel to auto-ignite in the combustion chamber. Auto-ignition is undesirable as it can lead to engine damage.
Pure Octane (C8H18) has a relatively high resistance to auto-ignition and is used as the standard for measuring this resistance.
The Octane number itself merely rates a given composition fuel as comparable in its resistance to auto-ignition as a standardized mixture of a certain percentage of Octane and Heptane.
A fuel with an 87 Octane rating merely means it resists auto-ignition as well as a reference fuel consisting of 87% Octane and 13% Heptane.
87, 89, and 91 Octane fuels are rated similarly by percent.
To simplify things a bit (we won't talk about impurities, additives, NOX generation and incomplete combustion into Carbon Monoxide), with Gasoline you get your energy by breaking high energy carbon-carbon and hydrogen-carbon bonds and creating lower energy CO2 and H2O compounds in their place. The sum total of the difference in bond strengths in a gallon of gasoline defines the energy you will get from that gallon of gasoline, about 125,000 BTU per US gallon.
Within a fairly narrow range within any gallon of gas NO MATTER WHAT THE OCTANE RATING there are going to be about the same number of carbon and hydrogen atoms, creating the same amount of CO2 and H2O. Thus within a fairly narrow range, all gasoline compounds will have very comparable energy contents per gallon.
The only time the octane level affects engine operation is at high load. If the car is geared sufficiently high enough, the load can be well above 50%, and with low octane can be on or above the detonation threshold. When this happens, the ECU responds by retarding the timing and the efficiency drops as a result.
If the local conditions (including the gas quality) don't allow the engines to run on 87 without retarding the timing, fuel economy will suffer. Changing to higher octane fuel will allow the engine to run at the programmed timing and get the expected efficiency.
As always, it's about how efficiently the engine converts the chemical energy to mechanical energy.
If the fuel economy improves by 20% when using gas that costs 15% more, money is being saved.
The opposite is of course true as well, but long term usage of low octane fuel in a high compression engine has other costs involved. Use the lowest octane fuel that doesn't cause detonation; the easiest way to check that is to see if your fuel economy is affected, so use the lowest octane fuel that gets you the highest mpg.
But then again, I could be wrong
The ONLY thing that Octane rating measures is the resistance of the fuel to auto-ignite in the combustion chamber. Auto-ignition is undesirable as it can lead to engine damage.
Pure Octane (C8H18) has a relatively high resistance to auto-ignition and is used as the standard for measuring this resistance.
The Octane number itself merely rates a given composition fuel as comparable in its resistance to auto-ignition as a standardized mixture of a certain percentage of Octane and Heptane.
A fuel with an 87 Octane rating merely means it resists auto-ignition as well as a reference fuel consisting of 87% Octane and 13% Heptane.
87, 89, and 91 Octane fuels are rated similarly by percent.
To simplify things a bit (we won't talk about impurities, additives, NOX generation and incomplete combustion into Carbon Monoxide), with Gasoline you get your energy by breaking high energy carbon-carbon and hydrogen-carbon bonds and creating lower energy CO2 and H2O compounds in their place. The sum total of the difference in bond strengths in a gallon of gasoline defines the energy you will get from that gallon of gasoline, about 125,000 BTU per US gallon.
Within a fairly narrow range within any gallon of gas NO MATTER WHAT THE OCTANE RATING there are going to be about the same number of carbon and hydrogen atoms, creating the same amount of CO2 and H2O. Thus within a fairly narrow range, all gasoline compounds will have very comparable energy contents per gallon.
The only time the octane level affects engine operation is at high load. If the car is geared sufficiently high enough, the load can be well above 50%, and with low octane can be on or above the detonation threshold. When this happens, the ECU responds by retarding the timing and the efficiency drops as a result.
If the local conditions (including the gas quality) don't allow the engines to run on 87 without retarding the timing, fuel economy will suffer. Changing to higher octane fuel will allow the engine to run at the programmed timing and get the expected efficiency.
As always, it's about how efficiently the engine converts the chemical energy to mechanical energy.
If the fuel economy improves by 20% when using gas that costs 15% more, money is being saved.
The opposite is of course true as well, but long term usage of low octane fuel in a high compression engine has other costs involved. Use the lowest octane fuel that doesn't cause detonation; the easiest way to check that is to see if your fuel economy is affected, so use the lowest octane fuel that gets you the highest mpg.
But then again, I could be wrong
06-01-12, 07:56 PM
#26
Rookie
Join Date: Jul 2011
Location: NY
Posts: 72
Likes: 0
Received 0 Likes
on
0 Posts
said this to my sister, she was putting 87 in her G37. car was sluggish, just not running fast enough to justify its price...
got her on 91 and the car speeds like a land rocket... most girls just really don't care about cars enough to maintain them besides cosmetics..
use the analogy of the effect on her skin if she used cheap ****ty make up all her life LOL!
got her on 91 and the car speeds like a land rocket... most girls just really don't care about cars enough to maintain them besides cosmetics..
use the analogy of the effect on her skin if she used cheap ****ty make up all her life LOL!
06-01-12, 09:43 PM
#27
Lexus Champion
Join Date: Mar 2011
Location: WA
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
Many people that have money got that way for a reason - penny pinching. I used to have a cheap-*** buddy that wouldn't even tip when we'd go out for lunch. But he had $50,000 cash in his bank account and owned two homes. At 22 years old. 
Saved every penny he earned.
Saved every penny he earned.
06-01-12, 10:22 PM
#28
So far there is not much difference in fuel mileage which is almost the same( i think ). I can't verify this exactly because my driving habits vary depending on my mood.
Acceleration seems much smoother. I might know this for sure once i switch back to my regular fuel of 95 octane.
My Lexus manual says to use 95 Octane fuel or higher. So I guess most of you guy's are already using slightly lower octane fuel's on your car's which is 91. On the other hand I think I'm wasting my money as 95 Octane would just be fine for me since there are no visible advantages and I'm not pushing my engine to the very limits.
I therefore believe 98 Octane should be used only for Sports cars since they have high compression engines. Anyways it's great Toymota is experimenting. We can learn something useful. There maybe a chance that he is right as well since he is not pushing his engine to the limits.
06-02-12, 12:33 AM
#30
I somewhat agrees with Toymota in the point that just because the car is design for premium gas to be run at spec doesn't mean it can't run with regular gas with some restrictions without much consequences (i.e. for the car to perform and run the way it's suppose to, premium gas is a must, but if you don't drive like that, it could be ok with regular).
Personally, I use premium gas on the car. If you don't want to use premium gas on principle and don't want to give the man extra 20cents, more power to you. If you just want to save 20cents per gallon that could cause problems later, then that's just dumb :p
Personally, I use premium gas on the car. If you don't want to use premium gas on principle and don't want to give the man extra 20cents, more power to you. If you just want to save 20cents per gallon that could cause problems later, then that's just dumb :p