Octane, and what it means to you...

[SmokingTires]

Since there seems to be a common misconception about octane, I thought I would go through and explain it for you

Octane rating tells you the fuels ability to resist spontaneous ignition under compression. Lower octane fuel (such as 87 octane) will be able to withstand lower amounts of compression than high octane fuel (like 92 octane).

What octane fuel you use will depend on what your compression ratio is. Lower compression vehicles (8:1 compression) will use low octane fuel. High compression vehicles (11:1) will need to use high octane fuel. Each engine has the specified octane that should be used in it.

Using the correct octane is important to the running condition of the car. If you use too low of an octane fuel, your engine will knock. Knocking is when the fuel ignites due to being compressed, instead of the spark from the spark plug.

If you use too high of octane fuel, not all of the fuel will burn. This causes carbon build-up to form on the inside of the cylinder. This will eventually cause problems with in your engine.


So to correct many misunderstandings, using higher octane gas does not create more power. It mearly shortens the amount of time before you need to rebuild your engine.

Hope that helped
Mike

[kenratboy]

But my Camry can use 87-91, or anything I guess.

Thats good. With current gas prices, 87 all the way!

[Warped]

Originally posted by alltrac165
The more efficient the combustion process, the less ignition advance and/or the lower octane required, all other things (such as CR and volumetric efficiency) being equal.

If I'm reading this right, does that mean my 95 1mz is pretty damn efficient if it has a CR of 10.5:1 and still run on 87 octane?

[alltrac165]

^That's partly correct, it is a pretty efficient chamber, but VE or Volumetric Efficiency plays a part as well. So an engine that can't breath really well can use a higher CR on low octane. The less air that gets into the cylinder means the less heat builds under compression, and vice versa. A friend of mine has an old Dodge Dart with a slant 6. These things have terrible heads. He can run 13:1 pistons because the thing can't get enough air in the cylinder to cause a problem. You'll notice that if you have an engine that requires high octane, and you run the cheap stuff, it only pings(or the computer pulls timing) under high load when the throttle is wide open and the cylinders are filling the best. That's because the CR is now a problem with the larger amount of air in the cylinder that has to be compressed. That is one of the reasons boosted engines generally use lower CR's. Engines designed for low rpm use and good mileage tend to have higher velocity ports which usually translates into lower overall VE. Higher CR is great for part throttle/cruise economy.

heres a couple links
http://auto.howstuffworks.com/question90.htm
http://chemistry.about.com/cs/howthi.../aa070401a.htm
and the mother of all octane links
http://www.imoc.co.uk/technical/article/octane.htm

[SmokingTires]

Originally posted by Wraith
Yes I work at a refinery ... I'm the big bald headed guy with the wooden spoon that stirrs the hot oil... lol

So wind at high speeds does have the power to blow your hair off?




Ok, I would like to make a point, and explain this to you guys. These threads I post, informing people of things like Octane, are very simple. They are meant for noobs and uninformed people. Which is why I don't go into exceptions like Turbos and engine build. Things like that would only confuse them.

I mean, I don't write these threads for you guys. I know you understand it. And the way I see it, by the time some noob is charging his engine, he will understand it too. So please, leave out your overly detailed corrections that everyone seems to feel the need to add. If I use the wrong name for something, please, feel free to correct me. But I don't want to make this harder to understand.

I think this might help explain my point...

Originally posted by Wraith
Mike, going into octane ratings its going to have to be pretty simple because ... Not everyone is going to understand what the hell we're talking about ...

Did I do good enough Wraith?

[VVT-i Owns]

Originally posted by alltrac165
^That's partly correct, it is a pretty efficient chamber, but VE or Volumetric Efficiency plays a part as well. So an engine that can't breath really well can use a higher CR on low octane. The less air that gets into the cylinder means the less heat builds under compression, and vice versa. A friend of mine has an old Dodge Dart with a slant 6. These things have terrible heads. He can run 13:1 pistons because the thing can't get enough air in the cylinder to cause a problem. You'll notice that if you have an engine that requires high octane, and you run the cheap stuff, it only pings(or the computer pulls timing) under high load when the throttle is wide open and the cylinders are filling the best. That's because the CR is now a problem with the larger amount of air in the cylinder that has to be compressed. That is one of the reasons boosted engines generally use lower CR's. Engines designed for low rpm use and good mileage tend to have higher velocity ports which usually translates into lower overall VE. Higher CR is great for part throttle/cruise economy.

heres a couple links
http://auto.howstuffworks.com/question90.htm
http://chemistry.about.com/cs/howthi.../aa070401a.htm
and the mother of all octane links
http://www.imoc.co.uk/technical/article/octane.htm

A higher velocity intake charge will give better low end torque and throttle resp. A lot of Japanese cars here have probably been remapped for the gasoline in North America. IE 1ZZ 10:1 CR

I've said this before and I'll say it again that in Asia the AKI of fuel is a lot higher.

FYI Volumetric Efficiency isn't static even with in an engine. It will depend greatly on RPM.

[dark_serphen]

if ur vehicles r equip with standard engines, then just use standard octane fuel. 87-91, cuz higher octane would causing to lower cat. coverter's life... which it could be burned out.

if ur vehicles r equip with high performance then definitely go for higher octane, @ least 91

just read ur damn owner manual

[SmokingTires]

Originally posted by bowlofturtle
hm... i've just read everything posted here twice. First off i never really understood compression ratios. Well now i under that the V6 camry has a high compression and it should use 93 octane correct?

Also the 4-cyl camry is high compressioned as well meaning it should also run on 93 octane.

By giving the car 87octane we are not letting the car breathe ?

So in general, all camry's should have 93 octane in them to aviod knocking since they have high compressions.

But what happens if you pur 87 in there and the car doesn't knock, will it die out in the long run?

V6 Camrys are higher compression vehicles, but now "high compression vehicles". V6 Camrys around about 9.6:1. High compression would be more around 10.5:1 or higher. I have found that the V6 Camry gets fine results with 87 octane, but runs a little smoother on 90 (or whatever your midgrade is)

Using 87 octane has nothing to do with breathing. Octane tells you the amount of compression the fuel can take before spontaniouslt combusting.

87 Octane will run fine in your car.


However, Unlike dark_serphen says, higher octane doesn't shorten your cats life. I don't know where you got that from. No matter what you are using, exhaust gases are all that go through the cat.