warminwisc

Not sure how it can be "night and day difference", but you won't even notice?Huh

Jabberwock

Agree - the ECU on the LS can detect how the engine is running with a given octane/grade of fuel and will make adjustments to avoid pre-ignition and to run as well as possible with a given fuel grade.

The theoretical expectation should be that lower grade fuel (ie regular versus premium) will result in some what lower mpg, performance and HP. It is fairly common currently for gas distributor to up ethanol content to boost octane in premium gas. Ethanol has less energy in it so you can end up with lower mpg with premium these days.

I can't recall ever seeing any objective study or set of measurements being published to verify or confirm performance and mpg results of different fuel usage in the LS. We have had anecdotal results via periodic posting by folks saying they use regular and get same, better, worse performance, etc - not much in the way of confirm-able usable data.

If I was on a budget and driving lots of miles I'd likely use regular in the LS unless I was driving mountains, high temp, or carrying heavy loads in the car where high octane premium would protect against load/temp induced knock.

LiCelsior

iTrader: (32)

go WOT on 87 and go WOT on 93..thats the difference.

edit: and the difference was in reference to the detonation..but the performance aspect is effected also.

hit it right on the nail.

XJSFan

I do feel a difference between 87/93. These cars were specd for 93 and that is what you should use. Mid grade may be OK but I know a Gas station owner and he told me that midgrade is not sold anywhere near 87 or 93 and can get stale in the stations tanks. I also do not think you should mess with any vehicles fuel system... If it calls for 93, then use it.

campisi

I can't tell you if there's a difference between 87 and 93 because I've always used 87 in my 03 since I bought it brand new. The only time I ever put 93 in is if I happen to be driving over a mountain pass in the summer or spend time in a place like Phoenix AZ in the summer. If you don't spend a lot of time with the pedal to the metal or quarter-miling then it's not one iota of an issue. My car returns about 26 MPG on the open highway using 87, cruising about 70-75MPH.

Gene01

XJSfan - I have seen the statement several times that the LS430 requires 93 octane, but can't figure out where that comes from (perhaps non-US owner's manuals). I am aware of the different countries' use of different standards for describing octane ratings. I have attached the page from the 2005 LS430 OM specifying the grade required in the US (91). Do you have a diferent source? Thanks.

aypues

91 is correct. That is all you can get in CA anyway.

Lavrishevo

iTrader: (1)

The LS430 does take advantage of higher octane fuels. It's a high compression engine. Don't forget that ethanol lowers the octane rating. You are really not getting 91 or our premium 93 on this side of town. The best mileage I see is when I run an octane boost or something like the Lucas fuel product. As high was 30 consistently mpg on the highway. For road trips it is well worth it. As much as 5 more mpg over 18 gallons is a lot. Have a heavy right foot and can't slow down a little? Don't bother expecting better mileage. 1700 - 2000 rpms is the sweet spot.

Here is a shot of pretty good mileage I got the other evening on standard 93. This was the average across 35 miles.

Jabberwock

Gasoline octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. It is so named because a fuel composed of 100% iso-octane has an octane rating of 100. Fuels which are less resistant to detonation than this standard are said to have an octane rating lower than 100, fuels that are more resistant than the standard to detonation have octane ratings greater than 100.
Since ethanol is less explosive and more resistant to detonation than iso-octane, it has an octane rating greater than 100. Ethanol octane rating is nominally 113. Mixing it will gasoline with a lower octane rating will boost the rating.

XJSFan

I will check but you may be right that it is 91. Here in Wi the stations have 93 octane... I probably should have stated that Premium is recommended.

jayclapp

My 04 Owners Manual clearly states 91 octane. People really should use their manuals more often for answers to questions.

Lavrishevo

iTrader: (1)

You are right. I was misinformed in regards to the octane. Ethanol does produce 33% less energy vs pure gasoline which is where the reduced mileage comes from.

Tom57

Over 500K miles over 20 years on 4 different LS's including 250K on my '01 running 87 octane. 25 mpg +/- highway @ 75+ mph. No gas-related issue whatsoever. Starts immediately in the morning at 15 below zero.

MPG is a function of so many contributing variables other than simply the "stated" octane rating (actual octane varies), including weather conditions (wind, temperature (cold better), humidity, tires including rolling resistance of tire rubber composition, tread configuration and tire pressure, wheel alignment, engine performance characteristics (fuel - air mix), spark plugs, mass air flow sensor, fuel injectors performance, choice of oil type/grade, combined weight of wheels/tires, and obviously whether the A/C compressor is "on" or "off." Having just replaced both of the oil control valve solenoids at 251K miles, even that has improved my highway MPG by 1 mpg due to their effect on more efficient variable engine timing. Oh, and my 5-speed '01 with over 250K miles gets better overall MPG than my 6-speed '06 with 60K+ miles. There is less internal friction in the higher mileage engine.

Definitely run premium.

XJSFan

In my 2006 Lexus manual it says premium unleaded gasoline with an octane rating of 91 or higher for optimum engine performance. In my state it is 93 octane and whatever you want to use is up to you...

KawiLex

I hate this thread.