How Many Of You Guys Use 87 Octane

[JasonInDallas]

There are so many misunderstandings and errors in this thread I have to step in and explain a few things:

1) Octane measures fuel's resistance to predetonation, which is when the air-fuel mixture explodes before the spark is applied. Basically the cylinder goes "boom" before it's supposed to. The higher the compression ratio of an engine (typical on high performance engines), the higher octane is required to prevent knocking and pinging. Knocking and pinging are the telltale results you hear from predetonation, and they not only reduce performance but are also bad for the engine.

2) Using higher octane than is optimal for the engine is a waste. That is to say if your car runs best on 91 octane then 93 has absolutely no benefits, since it doesn't have enough compression to predetonate the 91 octane so 93 would be no different. This bears repeating: octane's only job is to prevent predetonation, and all you need is good enough octane to prevent predetonation, and anything higher is a waste unless you rebuild yoru engine with higher compression pistons or otherwise (such as adding a supercharger which has the net effect of bigtime compression). Running 93 in a car that wants 91 is literally burning your money.

3) Most highly engineered modern engines have knock sensors, advanced metrics, and comprehensive engine management. In other words ther car watches what's going on in the engine, measures it, and then decides how to make adjustments for optimal operation many times a second - kind of like a continuous tune up as you drive. In a nutshel a sensor sits on the engine and "listens" for knocking which is caused by too low of octane. If it senses knocking, it retards the ignition timing which prevents predetonation. This is why a car that runs best on 91 can get by with a bit lower such as 89, however the retarded timing reduces performance which in turn reduces fuel economy thus negating any money you saved with the lower octane fuel.

In summary: run exactly the octane your car asks for and nothing lower or higher if you want best performance and best economy.

[Wilfred]

So what exactly is the recommended RON for a Lexus?

[Shareque]

We've driven 132K in a 93 LS 400 and 45K in a 2002 LX470 using primarily 87. Haven't noticed any difference between grades and have had no problems.

[AussiLS400]

In Australia we have 3 grades 91 regular, 95 premium & 98 super premium. The book here says to run on 95. I've run my car on all 3 grades and found that 95 gave the best power & economy. I found the minute i filled up with regular one day i could tell it had lost power and when i filled it again had used more fuel. I then tried 98 and it felt like it was underpowered again (not as much) but the economy was slightly better than the 95 and heaps better than the 91. I then refilled with 95 and found the power much better, smoother idle and the economy was good. MPG readings in litres were, 7.3 km per litre for 91, 8.1 km per litre for 95 & 8.5 km per litre for 98. The 8.1 is about 19 mpg city driving. I would suggest that you read the owners manual and run your car on what they recommend as this is what your car is set for.

[akewlguy]

NO MORE TRIPS IN THE LS. Just kidding, but today oil is above 66.. YIKKKKEEEEESSSSS

Looking forward to buying a scooter for local trips. Cheers

[90LS400Lexus]

Thats something I like about my 1985 Mercedes 380SE , is that it is not even required to run on premium fuel - it missed it by one year. Beginning with the 1986 model year, premium fuel was recommended for all Mercedes automobiles sold in the USA, save for the diesel models, (the 300SDL and 190D) which used diesel of course. :D

Whats more, I get 19-21 MPG in the city with my 3900 lb V8 Mercedes sedan. No, this is not typical either. Most people with the same car are getting around 15-16.

This car has 265K, I hope it lasts at least 20K more miles. :D

[nc211]

Premium...all the time. Put regular in there once, and won't do it again, car felt sluggish. Plus, at my mileage, the premium fuel cost "extra $2 bucks" is worth it to me to know that it's getting what it says it needs to run correctly.

[dole2000]

I used 89 a couple of times. Seems like I get a little better gas mileage with the 91. Did notice much differnce in performace.