View Poll Results: OCTANE - Which gas do you put in your 3IS
I always use 91 or higher.
259
91.20%
I sometimes use 89 or 87.
3
1.06%
I always use 89.
6
2.11%
I always use 87.
16
5.63%
Voters: 284. You may not vote on this poll
OCTANE - Which gas do you put in your 3IS and why?(merged threads)
05-31-14, 05:38 AM
#76
The pursuit of F
Thread Starter
We have 94 octane in Canada and I noticed the extra responsiveness. Problem is, it's 25 cents more per liter (almost $1 more /Gallon!!!)
05-31-14, 07:09 AM
#77
I feel the Shell 93 makes my car seem to run better, but Im sure its all in my head though. Can't be that much difference in gasoline
So on my way home I decided to fill up. Usually I put exon but decided to give the Sunoco gas station some business. Not really thinking I just pushed the gas all the way to the right when choosing which grade. While filling up I noticed 4 grades instead of 3 and realized I put 93 Octane gas rather than my normal 91. it was only 4 cents more per gallon so no big deal really . I paid $4.23/ gallon
Driving home I noticed a lot more pep and throttle response on just normal driving. What's the deal with this stuff? I've heard about it but never really knew what the true difference is, can anyone shed some light on this for me? I tried to Google it but couldn't find a definitive answer. Will the car benefit in the long run from using 93 all the time?
Also, what are your guys opinions on who has the best quality gasoline? Ive heard good things about BP, Shell and Sunoco. I know Sunoco is racing fuel so I cant imagine anything bad about it. Just trying to gain some knowledge here, Thanks guys.
Driving home I noticed a lot more pep and throttle response on just normal driving. What's the deal with this stuff? I've heard about it but never really knew what the true difference is, can anyone shed some light on this for me? I tried to Google it but couldn't find a definitive answer. Will the car benefit in the long run from using 93 all the time?
Also, what are your guys opinions on who has the best quality gasoline? Ive heard good things about BP, Shell and Sunoco. I know Sunoco is racing fuel so I cant imagine anything bad about it. Just trying to gain some knowledge here, Thanks guys.
05-31-14, 07:19 AM
#78
Lead Lap
05-31-14, 07:50 AM
#79
The pursuit of F
Thread Starter
I told my wife to fill up my car the last few times telling her to surprise me to put 87 once, back to 91, then 94 another random time. I was able to feel the slight difference, with 87 being a tad sluggish and 94 being the most responsive.
05-31-14, 10:47 AM
#83
My wife could not do that test for me, she is at look but don't touch status with the IS
06-01-14, 09:19 AM
#84
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93-94 octane is a good thing for any high performance car or any car designed to use premium. Manufacturers have to design ECU's to compensate for a range of octane ratings but cars that call for premium as per the manual usually have a fuel map designed for 93-94 octane gas. It comes down to the more expensive fuel being more capable of bringing the best performance your car can offer. It's more resistant to detonation and therefore your engine computer isn't pulling timing as much. With 91, 90, 89 or god forbid 87 your engine's power is severely limited by the computer because the lower the octane fuel the quicker it burns. This is fine for vehicles specifically designed to run on 87 or 89 100% of the time but not for a luxury car or high performance car requiring premium.
This is also why your manual states you CAN use very low octane fuel if you HAVE TO but only for as long as it takes to get to a gas station that sells higher grade fuel to top off with. Still, anything 91 or higher is considered "premium".
Perhaps it's apples to oranges but my SC was also tuned for 92 or 93 octane from the factory. It runs on the 91 we have in California just fine but power and ultimately some smidgen of fuel economy is sacrificed. There is a big difference between 91 octane and 93 or 94. I'd venture a guess that your IS doesn't need 94 octane but it should benefit from running 93 regularly. In Florida there is no 91 in most places, just 87, 89 and 93 so plenty of cars calling for "premium fuel only" run 93 all the time.
Beyond this, people with turbocharged cars need usually need the highest octane fuel that they can afford-- unless the manual says otherwise.
Someone else can better explain the physics of how different octane fuels burn in the combustion cycle, how high and low octane fuel and other byproducts are made from the same batch of crude oil and generally why high octane fuel is required for some engine designs but I hope this clarifies things a bit.
This is also why your manual states you CAN use very low octane fuel if you HAVE TO but only for as long as it takes to get to a gas station that sells higher grade fuel to top off with. Still, anything 91 or higher is considered "premium".
Perhaps it's apples to oranges but my SC was also tuned for 92 or 93 octane from the factory. It runs on the 91 we have in California just fine but power and ultimately some smidgen of fuel economy is sacrificed. There is a big difference between 91 octane and 93 or 94. I'd venture a guess that your IS doesn't need 94 octane but it should benefit from running 93 regularly. In Florida there is no 91 in most places, just 87, 89 and 93 so plenty of cars calling for "premium fuel only" run 93 all the time.
Beyond this, people with turbocharged cars need usually need the highest octane fuel that they can afford-- unless the manual says otherwise.
Someone else can better explain the physics of how different octane fuels burn in the combustion cycle, how high and low octane fuel and other byproducts are made from the same batch of crude oil and generally why high octane fuel is required for some engine designs but I hope this clarifies things a bit.
Generally, an engine with a high compression ratio (or effective compression ratio for Forced Induction engines) must use a higher octane fuel. This is due to the already high combustion temps and pressures associated with a high compression ratio. A high performance engine will always have a high compression ratio. The 2014 Lexus IS350's engine has a compression ratio of 11.8:1, which is considered fairly high for a N/A engine that is designed to run on pump gas. The higher the compression ratio, the need for a high octane fuel becomes necessary. Higher octane fuel's flame-front moves slower and more controlled than a lower octane fuel. This is especially important in an engine with a high CR due to the high pressures and cylinder temps. If lower than 93 octane fuel is introduced, the flame-front will propagate faster and more erratically, causing what's called "pre-ignition", which can lead to "detonation" if allowed to continue unabated (pre-ignition/detonation can be caused by other things as well). The ECU in a high performance engine application (like our Lexus IS350) is programmed to command ignition advance for maximum efficiency and power (with a built-in margin of safety) for 93 octane. The engine uses the "knock sensor" to listen for pre-ignition and detonation in the engine. A knock sensor is just a microphone, usually screwed into the engine block, that is tuned to hear certain frequencies that are associated with "knock" or "ping" from pre-ignition and detonation. Once the ECU "hears" the knock, it will begin to retard ignition timing using a complicated set of algorithms, to try to correct the knock. The ECU will keep track of what it hears and how much timing it had to pull to stop the knock. Most ECUs (especially forced induction), will have knock tables and an octane counter that will move the ECU slowly to a set of very conservative maps/tables as the knock-count rises. This is to protect the engine from an obvious bad-gas situation or a lower than tuned-for octane rating. As the ignition advance is retarded for a given load, the engine will loose power and efficiency.
Lower octane fuel already has less power potential due to loss of energy though heat, now factor in the loss of power/efficiency through retarded ignition timing and you get a very sluggish engine. If the engine is tuned for a lower octane fuel (lower compression ratio engines), going to a higher octane fuel will cause a lack of power as well, if the ECU doesn't advance ignition timing more to reach peak efficiency for that given octane. This is also holds true if you were to put 110 octane race fuel in your Lexus IS350. You would loose power unless your could re-tune the ECUs ignition advance. If you COULD re-tune for that fuel, you would gain a good bit of power. Now, some manufacturers run a lot of ignition advance for a given fuel and rely on the knock sensor to keep things safe. In this case, running an even higher octane than called-for can increase power as the ECU is already capable of commanding much more ignition advance as long as it doesn't hear any knock. Manufacturers do this to get the most fuel efficiency out of an engine as possible for low-load situations. But, there are many limitations to this. For instance, over-advanced timing will start to loose peak efficiency just before a knock condition. This also changes as the engine sees different loads.
There are also many other dynamic factors at play here, including air/fuel ratios, ambient air temps, barometric pressure as well as many other things.
Hope this somewhat helps without being too confusing.
06-01-14, 02:03 PM
#85
This is correct, but let's go a but deeper into the subject. This is very complicated and hard to write in a single post, so I will have to abbreviate this a lot. There are a lot of factors at play and I could write a book on each individual one as a former professional Dyno tuner.
Generally, an engine with a high compression ratio (or effective compression ratio for Forced Induction engines) must use a higher octane fuel. This is due to the already high combustion temps and pressures associated with a high compression ratio. A high performance engine will always have a high compression ratio. The 2014 Lexus IS350's engine has a compression ratio of 11.8:1, which is considered fairly high for a N/A engine that is designed to run on pump gas. The higher the compression ratio, the need for a high octane fuel becomes necessary. Higher octane fuel's flame-front moves slower and more controlled than a lower octane fuel. This is especially important in an engine with a high CR due to the high pressures and cylinder temps. If lower than 93 octane fuel is introduced, the flame-front will propagate faster and more erratically, causing what's called "pre-ignition", which can lead to "detonation" if allowed to continue unabated (pre-ignition/detonation can be caused by other things as well). The ECU in a high performance engine application (like our Lexus IS350) is programmed to command ignition advance for maximum efficiency and power (with a built-in margin of safety) for 93 octane. The engine uses the "knock sensor" to listen for pre-ignition and detonation in the engine. A knock sensor is just a microphone, usually screwed into the engine block, that is tuned to hear certain frequencies that are associated with "knock" or "ping" from pre-ignition and detonation. Once the ECU "hears" the knock, it will begin to retard ignition timing using a complicated set of algorithms, to try to correct the knock. The ECU will keep track of what it hears and how much timing it had to pull to stop the knock. Most ECUs (especially forced induction), will have knock tables and an octane counter that will move the ECU slowly to a set of very conservative maps/tables as the knock-count rises. This is to protect the engine from an obvious bad-gas situation or a lower than tuned-for octane rating. As the ignition advance is retarded for a given load, the engine will loose power and efficiency.
Lower octane fuel already has less power potential due to loss of energy though heat, now factor in the loss of power/efficiency through retarded ignition timing and you get a very sluggish engine. If the engine is tuned for a lower octane fuel (lower compression ratio engines), going to a higher octane fuel will cause a lack of power as well, if the ECU doesn't advance ignition timing more to reach peak efficiency for that given octane. This is also holds true if you were to put 110 octane race fuel in your Lexus IS350. You would loose power unless your could re-tune the ECUs ignition advance. If you COULD re-tune for that fuel, you would gain a good bit of power. Now, some manufacturers run a lot of ignition advance for a given fuel and rely on the knock sensor to keep things safe. In this case, running an even higher octane than called-for can increase power as the ECU is already capable of commanding much more ignition advance as long as it doesn't hear any knock. Manufacturers do this to get the most fuel efficiency out of an engine as possible for low-load situations. But, there are many limitations to this. For instance, over-advanced timing will start to loose peak efficiency just before a knock condition. This also changes as the engine sees different loads.
There are also many other dynamic factors at play here, including air/fuel ratios, ambient air temps, barometric pressure as well as many other things.
Hope this somewhat helps without being too confusing.
Generally, an engine with a high compression ratio (or effective compression ratio for Forced Induction engines) must use a higher octane fuel. This is due to the already high combustion temps and pressures associated with a high compression ratio. A high performance engine will always have a high compression ratio. The 2014 Lexus IS350's engine has a compression ratio of 11.8:1, which is considered fairly high for a N/A engine that is designed to run on pump gas. The higher the compression ratio, the need for a high octane fuel becomes necessary. Higher octane fuel's flame-front moves slower and more controlled than a lower octane fuel. This is especially important in an engine with a high CR due to the high pressures and cylinder temps. If lower than 93 octane fuel is introduced, the flame-front will propagate faster and more erratically, causing what's called "pre-ignition", which can lead to "detonation" if allowed to continue unabated (pre-ignition/detonation can be caused by other things as well). The ECU in a high performance engine application (like our Lexus IS350) is programmed to command ignition advance for maximum efficiency and power (with a built-in margin of safety) for 93 octane. The engine uses the "knock sensor" to listen for pre-ignition and detonation in the engine. A knock sensor is just a microphone, usually screwed into the engine block, that is tuned to hear certain frequencies that are associated with "knock" or "ping" from pre-ignition and detonation. Once the ECU "hears" the knock, it will begin to retard ignition timing using a complicated set of algorithms, to try to correct the knock. The ECU will keep track of what it hears and how much timing it had to pull to stop the knock. Most ECUs (especially forced induction), will have knock tables and an octane counter that will move the ECU slowly to a set of very conservative maps/tables as the knock-count rises. This is to protect the engine from an obvious bad-gas situation or a lower than tuned-for octane rating. As the ignition advance is retarded for a given load, the engine will loose power and efficiency.
Lower octane fuel already has less power potential due to loss of energy though heat, now factor in the loss of power/efficiency through retarded ignition timing and you get a very sluggish engine. If the engine is tuned for a lower octane fuel (lower compression ratio engines), going to a higher octane fuel will cause a lack of power as well, if the ECU doesn't advance ignition timing more to reach peak efficiency for that given octane. This is also holds true if you were to put 110 octane race fuel in your Lexus IS350. You would loose power unless your could re-tune the ECUs ignition advance. If you COULD re-tune for that fuel, you would gain a good bit of power. Now, some manufacturers run a lot of ignition advance for a given fuel and rely on the knock sensor to keep things safe. In this case, running an even higher octane than called-for can increase power as the ECU is already capable of commanding much more ignition advance as long as it doesn't hear any knock. Manufacturers do this to get the most fuel efficiency out of an engine as possible for low-load situations. But, there are many limitations to this. For instance, over-advanced timing will start to loose peak efficiency just before a knock condition. This also changes as the engine sees different loads.
There are also many other dynamic factors at play here, including air/fuel ratios, ambient air temps, barometric pressure as well as many other things.
Hope this somewhat helps without being too confusing.
08-08-14, 10:58 AM
#86
Gas Octane rating for IS350F
What's the factory recommended gas octane rating for this car? I have been putting petro Canada 94, but some forums suggested that petro Canada 94 = 91 plus additive, and Shell V power 91 is the best.
What's yours and what do you think is the best for performance and what is best for MPG? If you know any facts please share as well.
What's yours and what do you think is the best for performance and what is best for MPG? If you know any facts please share as well.
08-09-14, 05:31 AM
#89
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I noticed on the instead of the gas cap, it says use Premium Fuel Only even in the 250 ... but I put Regular in it.
I can't believe these engines need such high octane fuel, it's not like they are making crazy power. I'm not sure the compression on the engines, but I doubt these are high compression motors.
Technically, if these motors really need higher octane - then more than likely using regular unleaded fuel probably forces the motor to retard the timing, which means that you're car won't be as efficient or powerful if it was actually using the fuel it was designed for.
With that being said, if you're really looking for MPG's, the massive price difference between regular and premium wouldn't make up for the couple MPG different you'd potentially get.
If you're looking for power .. again, I don't know how much these cars really need higher octane fuel, but if they do, then that's how you'll get the most out of your car.
I can't believe these engines need such high octane fuel, it's not like they are making crazy power. I'm not sure the compression on the engines, but I doubt these are high compression motors.
Technically, if these motors really need higher octane - then more than likely using regular unleaded fuel probably forces the motor to retard the timing, which means that you're car won't be as efficient or powerful if it was actually using the fuel it was designed for.
With that being said, if you're really looking for MPG's, the massive price difference between regular and premium wouldn't make up for the couple MPG different you'd potentially get.
If you're looking for power .. again, I don't know how much these cars really need higher octane fuel, but if they do, then that's how you'll get the most out of your car.
