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Discussion Starter #1
the engine(2JZGE) in n/a form has a compession ratio of 10.5 to one... Soooo why does that need premium fuel? My 4AGE in my AE86 has 10.3 to 1 compression NO fancy engine management, and I can use 89 octane with NO issues... (no knock sensor to monitor knock)

So, why does the IS300 require premium? Engine management should be ok to deal with a bit of timing retard if needed.... so WHY premium????
 

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because they made the rated 215hp and 218lb-ft of torque on premium with high compression and timing, yes, the engine management can cope and pull timing, but you will lose power and get less gas mileage.
 
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Correct...the Ecu Can Compensate For Lower Octane. It Will Result In Poor Gas Mileage And Possible Pinging In The Engine.

Why Take That Risk ? :nono:
 

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You'll save like $90 over the course of a year if you drive as much as the average american and run regular gas....Stop buying your f'ing starbucks for a week and buy premium....
 

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Discussion Starter #5
First..... Never trust the internet! Many sources said premium... but the book just recommends it, with nothing lower than 87.

You make the most power with the MINIMUM octane! If the engine doesn't ping on a lower octane you will make MORE power from a lower octane than a higher one(look it up if you don't believe me)

I just read the manual...(wife's car, SHE read the manual) 91 is recommended... with nothing lower than 87! I'll stick with Chevron(can't beat Techron....) I'll have her drive using 89... I'll see what develops.


Tom - shut the #$&$* up... when I want advice like yours I'll ask the monkey at the zoo. Besides... Starbucks sucks... I have Dunkin shipped to my home bi monthly.


A back handed intro(I'll post up more later) I have 30 years in the auto industry, I've enjoyed a few euro models, a few domestics... and a few asian imports... Some of my rides have been....

1966 Shelby GT-350H
1970 Mustang Mach 1 428 SCJ
Volvo 1800 (1 E model, 2 S models)
Volvo 122S(2 owned by the wife)
1969 Alfa GTV 1750
AE86 - 2, one stock, daily driver(loooong gone) one mildly modified balck street coupe
1968 Pontiac GTO Ram Air III
1969 TVR Vixen S2
1964 Opel Kadett 1100
A few other makes and models I don't recall at this time.
 

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First..... Never trust the internet! Many sources said premium... but the book just recommends it, with nothing lower than 87.

You make the most power with the MINIMUM octane! If the engine doesn't ping on a lower octane you will make MORE power from a lower octane than a higher one(look it up if you don't believe me)

I just read the manual...(wife's car, SHE read the manual) 91 is recommended... with nothing lower than 87! I'll stick with Chevron(can't beat Techron....) I'll have her drive using 89... I'll see what develops.


Tom - shut the #$&$* up... when I want advice like yours I'll ask the monkey at the zoo. Besides... Starbucks sucks... I have Dunkin shipped to my home bi monthly.


A back handed intro(I'll post up more later) I have 30 years in the auto industry, I've enjoyed a few euro models, a few domestics... and a few asian imports... Some of my rides have been....

1966 Shelby GT-350H
1970 Mustang Mach 1 428 SCJ
Volvo 1800 (1 E model, 2 S models)
Volvo 122S(2 owned by the wife)
1969 Alfa GTV 1750
AE86 - 2, one stock, daily driver(loooong gone) one mildly modified balck street coupe
1968 Pontiac GTO Ram Air III
1969 TVR Vixen S2
1964 Opel Kadett 1100
A few other makes and models I don't recall at this time.
I'm not saying anyones right at this time but I can now see why people are ditching my.is for other IS sites. All anyone is doing is asking for advice. Thats it. STOP dissing each other. Well at least on forums.
 

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First..... Never trust the internet! Many sources said premium... but the book just recommends it, with nothing lower than 87.

You make the most power with the MINIMUM octane! If the engine doesn't ping on a lower octane you will make MORE power from a lower octane than a higher one(look it up if you don't believe me)
First, chill out, tom just drew a comparison on how much the difference is using starbucks.

So this is why race gas is well over 100 octane? Higher octane gas burns at a higher temperature, avoiding pre-ignition and knock allowing you to run more compression and more timing to get more power out of the motor. Yes, the ECU will compensate by pulling timing, but you will lose some power and you do risk knock problems.
 
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this is what i do. cheap car cheap gas. expensive car expensive gas. =)
 

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man last night i calculated 14.4 mpg :shocked: i always run 93 octane. what do they do to gas in the winter out here???
 

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I'm not saying anyones right at this time but I can now see why people are ditching my.is for other IS sites. All anyone is doing is asking for advice. Thats it. STOP dissing each other. Well at least on forums.
Seriously we are suppose to be looking out for each other on this website, not who is better and admit when you are wrong.. its not about who has the longest dick, lol, I agree with you man..
 

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First, chill out, tom just drew a comparison on how much the difference is using starbucks.

So this is why race gas is well over 100 octane? Higher octane gas burns at a higher temperature, avoiding pre-ignition and knock allowing you to run more compression and more timing to get more power out of the motor. Yes, the ECU will compensate by pulling timing, but you will lose some power and you do risk knock problems.
You took the words right out of my mouth.;)
 

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Discussion Starter #13
I have no problem with anyone... But, for my first significant post, Tom was less than friendly, and with no pertenant help/information! I apologize for "slapping" him

Has anyone run the car with an OBD II reader ON and SEEN if the ignition pulls??? Why would you assume something when it comes to power and gas mileage??? The one Achilles heal I read about PRIOR to buying this for my wife was the IS300's gas mileage. Soo... if running on 89 still perform perfectly why wouldn't you???? Expensive cars DON'T always = Expensive fuel.... Perfect example(albeit a bit extreme) would be the diesel racing R8 Audis.... who would think you could run a winning racing car on diesel......

Another point...... this is our daily. this will never be thrashed THAT hard.... I may enjoy it once in a while... but if I want to play, my AE86 is more than enough to enjoy the twisties with.
 

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$44.00 to fill up today. On a nearly empty tank. :(
 

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Honestly.. I run on Chevron 91 octane just because thats what I hear most, that choice is the best way to go.. I dont know if its true to just go with 88,87, or even 85 to save money but I just would rather be safe then sorry..
 

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interesting. bastards
I had never heard of oxygenated gas before this... definitely interesting. Although, now living in Ohio, I don't know if the gas is oxygenated like in CA, but I can attest that mpg is worse in my car, and my wifes fx35 by quite a bit in the winter time. I had attributed this to the cold temps making the oil more viscous and creating more drag on internal rotating parts. that, or, possibly the greater oxygen density of cold air causes more fuel to be dumped in by the injectors to keep a consistent A:F ratio??? just thinking of hypotheses. all I know is my mpg is always better in the summer.
 

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Welcome to our inbred board oldeskewltoy. We're not the most polite group, and like to bicker, but stay around...you might like it. And we can always use some schooling.

As for the octane issue...it's really a matter of ignition timing. Octane will make you more power, albeit probably minimally, if the ECU takes advantage of it with more timing. The OBD-II doesn't allow you to log knock count like some OBD-I system. I have not logged stock timing for octane...however, I know there is not much room to advance stock ignition timing much without getting audible knock before the ECU pulls timing with 91octane.

The car will more than likely run fine with 89 octane. Since it has knock sensors, it will simply run a retarded map. The only thing I can suggest is to stick with one grade so the ECU doesn't have to hunt for optimal timing with every fill. Modern ECUs, will try to extract the most efficiency they can unlike old cars that have to run the lowest common denominator tune. If the $90 saved annually is worth the few % efficiency loss (hp and mileage), than that is your prerogative.
 
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I'll toss in my .02c as well.
Engineers (guys with smarts) determine the minimum and recommended fuel octane to use in an engine based on their testing, notice key word "recommended". Which in the case of the IS350 is "ONLY", key word "ONLY".
Can you get away with regular gas in a premium recommended engine,....I would say yes, with all the caveats previously posted.
Should you use regular in a premium only engine,....I would say no, because the guys with smarts designed the engine to give it's best using premium for all the reasons we don't know.

Compression ratio is only one part of the complicated puzzle of what octane fuel you can use in an engine,.......cylinder head design, fuel charge, flame front propagation, N/A, boosted,......on and on.
i.e. My son's '89 ALL-TRAC is about 8.5:1 compression ratio, but because it is turbo charged, you CANNOT RUN anything less than 91 minimum, we use 93.
 

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not to stoke the fire but i work for lexus. have been a tech there for many years. in the training i have been to in the past we went over this very topic.
yes most cars will run on normal 87 gas. no brainer. but for the computers that these cars run it is programed for premium fuel. we had issue with shifting concerns on a few different models. it really all came down to the type of fuel. like listed before the ecu will take timing out when it has to. in turn over ther learning curve of your ecu/car it see less timing and less agressive mapping. and that directly affects shifting in automatics. we do tons of studies research and such. it was even recorded on our cars that you will save money on using premium over a course of 3 tanks or so. the longer it lasts the less you fill up.

plus if you add it up its not that much. gas difference is like 20 cents between the grades. 16 gallon tank fill thats 3.20 more for each fill.
 
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