ummagawd

iTrader: (1)

I tried it to see if it would ping... and everything's fine. In fact I'm getting slightly better mpg now that i'm putting in 89.

chanh55

Isn't the difference between 89 and 91 only about $0.10? If so... if you had to fully fill your 20 gallon tank, you're only saving $2.00. So for saving $2.00 to fill a full tank, I don't think the risks of harming your engine is worth the savings.

ummagawd

iTrader: (1)

well... like i said i just wanted to see if it would ping/bog/etc... and it runs like a champ... plus the slower burning 89 gives me more mpg

JLAM

iTrader: (1)

<--- stickin with 93 octane.

BlackSeat

If you put 87 into your car, it still won't knock noticeably. The ECU will immediatly detect lower octane (knock sensor) and switch to a diffrent fuel/timing map. Low octane generally only lowers your MPG (if your using it in a car that requires a higher octane) and performance (i.e. retard ignition timing). I'm suprised that your MPG actually went up.

If I could I would use 93.

LexusPunk

I've used it for awhile now...no big whoopdy doo, but I am saving a $105 dollars a year by switching to 89

ummagawd

iTrader: (1)

i was boggled by this too actually

BigWaveSC

iTrader: (5)

Wow I wondered about using lower grade gas, but whatever.
in San Diego they only sell 91 for premo whats up with that.?

Neo

iTrader: (3)

Nope. Not liking the pricing like many of you but I'm sticking with premium.

DetMich1

I started using 89 octane gas in my 1992 SC400 years ago. I would estimate I have put on over 100,000 miles using the mid-grade fuel. Have never suffered any noticeable knock or loss of performance. I have driven the car over 351,000 miles with NO drive train related issues at all. 14 year old car still has original engine, tranny, drive shaft , differential, universal joints, even the exhaust system is still original. The mufflers on my American cars never lasted more than 3-4 years. Just replace fluids, brakes tires, reccommended routine maintanance. Most reliable and durable car I have ever owned. I hope my other Lexus' last as long.

CVsIS250

This post is not meant to offend anyone BUT...if you can afford a 50-60K ride, why would a $.10-.20 difference in gas prices mean anything to you?

CV

ummagawd

iTrader: (1)

non taken.... but i suppose its the same reason why businesses spend countless resources to see where they can save money.

CVsIS250

True that! I do believe that the more money you have, the tighter you are. I buy myself nice things, but I sure don't spend frivilously. I get tired of worrying about two things in my life, keeping in shape and gas prices. I've promised myself that I would only let one of these things control my outlook. You can guess which one. I am sure not going to cheat my car for $2.

CV

BlackSeat

Only one explanation:
Its a Toyota! Energizer should use Toyotas instead of the stupid bunny to illustrate their point.



Seriously, I wouldn't expect the difference between mid grade, and high grade to be all that diffrent. Especially in a V8. For that matter the drivetrain would be the last thing affected by lower octane.

Either way todays ECUs are all tuned toward using a certain octane of gas. The whole idea of higher octane is simply that it has a higher tolerance to preignition and detonation than lower octane (contrary to popular belief, higher octane does not equate to higher quality). By switching to lower octane you've effectivly lowered the preignition/detonation threshold (with all other things being equal).
The two simplest ways to get around this is:
a) "richen" the air/fuel ratio [increase fuel injection, while keeping consumption the same {this leads to lower fuel efficiency}], and,
b) "pull back" ignition timing [the spark arrives increasingly later in relation to the original spark timing - which allows the piston to reach closer to top dead center before ignition {this leads to less available power}].
This is all done in the ECU itself. Though they are a few other factors that cannot be avoided or changed when choosing the octane.
By far the most important factor of this type is the Compression Ratio (CR). Increasing the CR as a means to increase performance, will also increase the likelyhood of preignition and detonation. In terms of simply Chemistry, this comes down to thermodynamics. Increasing pressure-or-decreasing volume will increase the systems energy (1st law of TD). During combustion, majority of this energy is turned into heat (and a smaller portion is turned into sound and work). In all reality its a system of diminishing marginal returns (strictly in terms of power and heat ~ higher CR can also increase fuel economy). You may get more work out of it (i.e. more power), but your also getting a disproportionately larger increase in heat. In this sense, the CR is directly related to amount of heat in the combustion chamber and in turn the octane rating required. With that said, the 2IS come with a ridiculously high CR (somewhere around 12:1). For comparisons sake, my '00 Mitsubishi V6 has a CR of only 9:1 and still requires premium grade in order to make peak power
The other factors that affect the octane required include total displacement, the amount of output per liter, and environment (altitude, temprature, humidity).

Though in all honesty I suppose if your not flooring it all that much you might not really notice much of a differance. Even more so by switching to a slightly lower octane (as opposed to simply using 87). As for the thread starters original post, I can only theorize that a combination of events lead to seemingly increased MPG with lower octane. Maybe the ECU didn't pick up on the lower octane (after all, the ECU can't readily detect lower octane ~ it can only assume your using lower octane by how the engine behaves)...though I'm not entirely sure how that would increase MPG.

If you really want to see the difference in octane, wait for a hot-dry sunny day (triple digits if possible ~ Death Valley kinda hot). After you've emptied your current tank, try out a few gallons of 91 first. Drive your car enthusiastically till your empty again (I assume no liability for your own interpretation of enthusiastically ). Then try out some 87 with the same conditions as before. Heck if you have an intake you might even notice the differance in your engine sound.

edit: Sorry for the lecture, though I figured some of you guys might want to know why you bother putting in 91 instead of lower grade...I'm sure its not airtight, though thats the basic idea.

StasGS4

iTrader: (1)

I completely agree with BackSeat. Another key point to 89 octane gas is that it is a blend between 87 and 92/93. In fact the mid grade (89) gets blended directly at the gas station. So in turn you are still getting a fraction of the premium fuel when you purchase 89 octane.