Very interesting info...sorry just reading what everyone is saying. I run 91 right now but it's only my second tank since I got the car 2 weeks ago. What are these "pre-ignition" probs. that everyone is talking about with lower octane fuel?

 

I would be honest with her, tell her the manufacturer recommends 91 octane, then show her the couple spots in the car where it says "premium fuel only" and then offer to pay the difference between 87 and 91.

With a tank and 1/2 it might come out to a $6.00 difference.

Problem solved.

 

Super (91) here is at $4.09/gal. By the time i take the trip it will most definately be higher than that.

 

just run 89 its in the middle of both!

 

Some cars (and most motorcycles) don't really require premium fuel... it's just a sales gimmick.

BUT.... i tried regular in my '96 LS for about a year and it slowly, and slowly and slowly got worse and worse gas mileage. I was a doubter myself until I witnessed it. I guess Lexus really does engineer their cars for premium. lol.

Anyway, I was getting a little over 14mpg at one point so I switched back to premium and after about 6 weeks, I'm up over 20! NO JOKE! I've always randomly checked the MPG just to hopefully spot a potential problem when it might arrise so I know this is accurate.

Look at the current prices and you'll see that even the extra $ for premium over regular WILL STILL PAY OFF WITH THE IMPROVED MILEAGE! At least it did for me.

 

Thanks for the information on the different grades of gas I have been using 89 octane and driving some days 250 miles a day and gas here in California is now $4.12 to 4.20 for 87 octane which I will try and run. I have been using Arco gas which a lot of people say is bad gas I put 102,000 miles on the platium plugs and they were clean and gray and no build up I am now testing
IRIDIUM plugs and the car runs even better getting about 24mpg not bad for California traffic and bad roads.

 

pre ignition or detonation, happens when the low octane fuel explodes under compression before the spark plug lights off the mixture. this causes the rod, piston and crank to be put under HUGE amounts of stress becuase the explosion is causing hte assy. to want to move back down before it's actually ready to; because another rod/piston assy. is already doing that.
octane is the resistance to explosion under pressure. that way we get our explosion to happen right when it's supposed to, controlled by the spark plug.

 

Yup, but I thought once the knock sensor detects the detonation, the ECU kicks in and retards the timing, hence why you would get the lower performance...

Of course, intake temperature is a variable in this equation as well, aint it?

 

you are correct. i was just explaining what pre ignition is to Greek.
intake temp won't really have a large effect on our n/a cars. on turbo cars, high intake air temp can cause more power loss.