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Discussion Starter #1
Is Premium gas a must???Has everyone been sticking to the rule?? It says on the gas fill door use Premium gas only, however the manual says 89 octane or higher??? What is everyone using and does it make a huge difference if you use 89 (midgrade)????
 

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In my opinion it doesnt matter between midgrade and premium..every article I have read says there is no difference. It just makes you feel better and takes more out of your pocket. So go figure


K
 

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There is no difference between the 87 and the 92 octane gas, the only thing that the 92 will do is prevent knocking better than the 87. You will not see a difference in performance in your IS by putting an 87 rather than 92, unless you are at a very hot area where knocking is possible. If you still want more fact to support this, go to any library and read documents on combustion chemistry. You will see there is no difference.
 

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i dont' know the compression ratio on the is300, but with cars taht have high ocmpression ratios, you need higher octane fuel
 

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you are right on that one, but with the compression ratio modern car uses, you usually don't have to worry about knocking under regular driving condition. The only engines you will have to worry about are the force induction engines.
 

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There's a simple test anyone can perform.....

Try use 87 and do an acceleration test, then fill her up with 92 and THEN do an acceleration test......

Then tell us if there's a difference.....speedwise, noisewise, and smoothness of the motor.....

Especially in the high RPM range....


[This message has been edited by dude (edited September 04, 2000).]
 

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If the manual says 89 octane, you should use 89 or higher octane gas. Don't go by Premium or Midgrade labels until you read the octane rating. Some places have 87 or 89 midgrade, some have 92 or 93 or even 94 premium.

For maximum performance with minimal knocking, use the recommended gasoline: 89 octance. You can try 87 or lower if you want, but it is likely performance will be suffer (the engine is avoiding knock) and if you hear audible knocking, you should go definitely go back to 89 or higher.

There is no difference between the 87 and the 92 octane gas, the only thing that the 92 will do is prevent knocking better than the 87
The difference is is that the higher octance gas has a higher "flash point" than the lower octane gas. That is a critical and important difference. The octane in a gas is a measure of how hot and bothered (compressed) a gas can get before it ignites. When you run a high-compression NA engine (like the IS, although the IS does not have a really high compression engine) or a forced-induction engine (turbo or super-charged) you really want all the octane you can get. If the engine is knocking or is trying to prevent knock (via on-board systems in newer cars or aftermarket devices like MSD or J&S) it is retarding the timing. If you (or the engine) are retarding the timing, you are not getting the maximum power out of the engine.

It's up to you what gas to put in. But 89 octane is in the manual for a reason. Lexus doesn't get kickbacks from Chevron.

with the compression ratio modern car uses, you usually don't have to worry about knocking under regular driving condition. The only engines you will have to worry about are the force induction engines.
Modern cars don't all have the same compression ratios. The higher the performance figures for a given size displacement engine, the higher the compression ratio is likely to be when normally aspirated. However, many modern cars have their own knock sensors and can retard timing when knock occurs.

And another thing, ever wonder what race gas is? It's gas with a very high octane rating, usually around 104. And octane boosters? Race gas allows engines to run with more advanced timing and/or more boost without knocking and pinging. In case some of you didn't know, knocking and pinging are signs of premature detonation (the gas has ignited due to compression before the spark has lit). This is bad. When bad enough, it causes engines to explode. In fact, in rotary engines, one simple ping is enough to blow apex seals...

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Tony
'01 Spectra Blue
'94 Turbo Miata



[This message has been edited by webmaster (edited September 04, 2000).]
 

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Wow, you explain pretty much what I learned in one combustion class in just a few paragraphs. Pretty good.
All I was trying to say is for everyday driving, lower octane gas shouldn't matter and racing gas will not give us any advantage because of the ignition timing we are using.
For example, my combustion professor, who is one of most well known engineers in this field (if you are at UCI you will know who I am talking about), drive a Lexus LS400 and usually use 87 Octane gas. The reason being that out of one barrel of oil, only about 10 - 15% can be refined to 92 or higher octane gas, while around 50% of the barrel can be easily refine to the 87 octane gas. This is the main debate behind whether or not they should just use one grade of gas, 89 octane, so pollution can be reduced.
Well, I know most of us will still use the 92 octane anyway.
 

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ok, lexus owners bitching about saving 10-20 cents a gallon, what next? pumping gas at a arco outlet? refurbished? irregular gas? try a few different types and brands then stick to whatever made your car feel best...
 

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We went through this whole debate in an earlier thread...

Anyways - Lexus doens't make any money off of gasoline sales - so they have no reason to recommend needlessly expensive gas.

You should follow their recommendation.

Trying to second guess based only on compression ratio is a mistake. There are lots of other factors - combustion chamber shape, spark plug temperature, etc, etc.

My modfied (extra boost) supercharged MR2 pings on 92 octane Arco or Shell gas, but runs great on 92 octane Chevron gas... A mechanic told me to use Chevron premium when doing emissions tests. Chevron tends to cost a bit more, but I think they use superior additives.

My wife's Mercury Sable says that it runs fine on "regular", but we have to run 89 octane when driving uphill in the mountains otherwise it pings.

Another thing to consider is that gasoline varries regionally - some places uses Ethanol mix. Some add oxygenating agents for emissions purposes.
 

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Discussion Starter #16
Thanks for the info guys. I wasn't bitching about the price of the gas. I was just trying to clear up the confusion of what the manual said. I will continue putting premium gas in it. Sorry I sruck a nerve with you Don C. Just trying to get some info!

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you didnt strike a nerve, i was just commenting how its ironic that some ppl would spend 35k for a car yet worry about pocket change...i can care less what you put in or on your car cause its your car, it just strikes me as funny when i see all these ppl driving luxury cars buying second rate stuff all for a few pennies...like i said, try a few and stick to what you like, i wouldnt worry too much as to what the manual says as long as you meet its minimum since the ppl who wrote it should know whats good for the car. for me, its the top of the chevron line for my IS300
 
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