I read many informative posts on this site, some scientific and some speculative but truly nothing very conclusive. Even emails to Toyota drew little assurance. I historically ran Regular gas in my LX with great results even while towing. I recently found a very good source of 93 Premium as local Sams Club opened up gas station. They only offer 2 grades of gas Regular 87 for $1.995 and Premium 93 for $2.279, well that made me think, why not. With very little tuning experience I geared up with real time OBD2 device and programmed some custom gauges and gave it a go.
Hopefully we could get some experienced tuners involved in this conversation.
Couple of conclusions from prior posts were that all 200 Series cars run well on regular gas. Slight improvement in mpg is so minimal that it does not justify higher cost of Premium. Another one is that both Toyota and Lexus use the same engine configuration and the same engine ECU - it is the same part number and likely same programing for LC (requires Regular 87) and LX (requires Premium 91) Lexus tech specs list slightly higher HP (close to nothing) and Torque.
So rather than beat on the dead horse, Toyota truly no help, I did some real time monitoring and on line research and found some valuable information.
My conclusion to date and I could be wrong - it s all in the software. Did not I just say both LC and LX use the same software? Well that is correct. My current conclusion is that our stock 5.7 is fully capable of running both Regular and Premium. What is of importance is to be consistent with what you put in your tank and not to switch back and forth between grades often as by doing so you would give your ECU a rather hard time figuring out which tune to use.
Well I just gave out the answer. My research and testing leads me to believe, that a ECU stores multiple tuning tables. Looks like there is a High Octane Table (better performance with more advanced timing) and Low Octane Table. Depending on how sophisticated programming is, there could also be an additional in between hunting table for those who switch between grades often or for situations where you fill up with some bad gas.
So how does it work? Well you decide what grade of gas you put in your tank and that is about all you can do unless you are into custom chips and advanced tuning. ECU software does the rest. It monitors the knock sensor microphone output at various above idle RPM ranges. If it dectects knock it updates real time tables and looks for consistency and reoccurrence in predetermined RPM ranges. Based on the data it collects over time (May take a full tank or 2) it adjusts your knock PID parameters like Knock Correction Learning Value and Knock Feedback Value. It takes time as it looks for consistency and that is where you can help. If you buy SheLL Premium - stick to Shell premium, if you buy BP Regular - stick to BP Regular. I believe it is consistent Knock Feedback Value ECU uses to determine if it should use High Octane or Low Octane Tunning Profile table. 89 Octane could be your worst choice as your ECU could go into constant hunting mode (kind of undecided). If you run 89 mid grade it is likely you are not doing your ECU a favor at all.
I believe the true reason why Lexus manual calls for a Premium 91 Octane is simply the luxury aspect of the brand and they want us to have better overall experience with best possible performance, hence they want us to use High Octane Tuning table.
I believe If you own a LandCruiser you would accomplish same results and performance gains benefits with Premium, most important more timing advance = unquestionably more power. Keep in mind that process takes time - up to 3 tanks full according to some tuners for you to notice (or not) the benefits.
Hopefully we could get some experienced tuners involved in this conversation.
Couple of conclusions from prior posts were that all 200 Series cars run well on regular gas. Slight improvement in mpg is so minimal that it does not justify higher cost of Premium. Another one is that both Toyota and Lexus use the same engine configuration and the same engine ECU - it is the same part number and likely same programing for LC (requires Regular 87) and LX (requires Premium 91) Lexus tech specs list slightly higher HP (close to nothing) and Torque.
So rather than beat on the dead horse, Toyota truly no help, I did some real time monitoring and on line research and found some valuable information.
My conclusion to date and I could be wrong - it s all in the software. Did not I just say both LC and LX use the same software? Well that is correct. My current conclusion is that our stock 5.7 is fully capable of running both Regular and Premium. What is of importance is to be consistent with what you put in your tank and not to switch back and forth between grades often as by doing so you would give your ECU a rather hard time figuring out which tune to use.
Well I just gave out the answer. My research and testing leads me to believe, that a ECU stores multiple tuning tables. Looks like there is a High Octane Table (better performance with more advanced timing) and Low Octane Table. Depending on how sophisticated programming is, there could also be an additional in between hunting table for those who switch between grades often or for situations where you fill up with some bad gas.
So how does it work? Well you decide what grade of gas you put in your tank and that is about all you can do unless you are into custom chips and advanced tuning. ECU software does the rest. It monitors the knock sensor microphone output at various above idle RPM ranges. If it dectects knock it updates real time tables and looks for consistency and reoccurrence in predetermined RPM ranges. Based on the data it collects over time (May take a full tank or 2) it adjusts your knock PID parameters like Knock Correction Learning Value and Knock Feedback Value. It takes time as it looks for consistency and that is where you can help. If you buy SheLL Premium - stick to Shell premium, if you buy BP Regular - stick to BP Regular. I believe it is consistent Knock Feedback Value ECU uses to determine if it should use High Octane or Low Octane Tunning Profile table. 89 Octane could be your worst choice as your ECU could go into constant hunting mode (kind of undecided). If you run 89 mid grade it is likely you are not doing your ECU a favor at all.
I believe the true reason why Lexus manual calls for a Premium 91 Octane is simply the luxury aspect of the brand and they want us to have better overall experience with best possible performance, hence they want us to use High Octane Tuning table.
I believe If you own a LandCruiser you would accomplish same results and performance gains benefits with Premium, most important more timing advance = unquestionably more power. Keep in mind that process takes time - up to 3 tanks full according to some tuners for you to notice (or not) the benefits.
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