Spade

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

Spade

Let's add some more crap.

Of all the vehicles that I could find on the internet with a 9.6:1 compression ratio, 87 was the recommended octane!
10:1 or higher got the 91 recommendation.

Spade

Man, No one wants to comment? Interesting.

mattjohnston

Posted in the other thread also.... What about 110 Octane fuel, and 107 etc...? cant be 110%

?

just wondering.

isotopesope

i swear i get better gas milage with 91 octane. i've only used 91 in my current civic and previous civic. not that this has any technical value as the first post, butt hay.

4g4me

GOOD question

Pho Real

110 octane booster is concentrated.... but when you add a few ounces of it to about 10 gallons of 93 octane you wind up with about 94 octane gas....

Spade

Driving style too.......I consistantly got 30 miles to the gallon in my HX and now in my EX I get a constant 32 to the gallon.

I don't need to down shift to 3rd to pass on the freeway.

WAFFLES

bump

motomullet

what about the actual 112 octane fuel? Like the crap thats 5 bucks a gallon that i run in my motocross bike? That stuff isn't 93 octane pump gas and an additive. If it was pure octane, wouldn't it be 100% (100 octane??)

Spade

http://www.howstuffworks.com/framed....ing/leaded.htm

LEAD additives.....

motomullet

I'm talking 113 klotz un-leaded race fuel, not nascar lead fuel.

Spade

Here is the link..... http://www.howstuffworks.com/question90.htm

g_man80

Now that we are talking about compression and recommended octane, what kind of compression am I looking at with my '96 b18b? And what octane do you recommend?

Spade

87....stock B18's have a CR of 9.2:1

madtownhonda

Octane is a rating system. If you have solely Heptane and Isooctane, then it is a simple percentage. An octane rating of 0 indicates pure heptane, an octane rating of 100 is pure isooctane. The reason some have a rating of more than 100 is because of them have additives that have a higher octane rating. MTBE (methyl tertiary butyl ether) is one of those. Pure MTBE has an octane rating of 110. So if combined with a 94, it will raise the rating. MTBE oxygenates the gas, and reformulates it. Other oxidizing additives are ethanol and methanol. The reason these were introduced is that oxygenated gas burns more completely that does it's counterpart. When gas doesn't burn completely, the CO2 (carbon dioxide) product is increased as well as other volatile products of the combustion. It's part of the Clean Air Act back in the early 90s.

So if you wanna pass smog, put some high octane gas in your car. It will burn a lot cleaner.

The downside, it REDUCES FUEL ECONOMY. Why do you think you get worse gas milage in winter! The cold causes an even more incomplete combustion and they add more additives. So if you ever noticed that you get worse gas milage in winter, that is why. I know I'm enjoying my 35mpg on 87 octane gas right now. I get about 5% worse milage in winter.

****, I think I got all that right. I could have left some stuff out too.

g_man80

So, any advantage to running a higher octane in an engine that doesn't require it? A NA engine. And what is the compression of the B18C, b/c the owner's manual recommends a higher octane.

madtownhonda

I run 87 octane...never heard knocking so I don't use any higher. Performance gains are negligible between 87-93.

BTW: the lowest octane gasoline will probably not cause knocking on fuel injected engines. The reason they made higher octane fuel is because of carbs. Carbs don't control the A/F mixture nearly as well as fuel injected cars. The ECU controls the A/F under all types of conditions where carburators need to be adjusted if it isn't right. Anyways, I just recommend to use what the owners manual says. I just use 87 because I'm cheap.


[Modified by madtownhonda, 9:17 PM 7/2/2002]

Spade

THe B18C1 has the compression ratio of 10:1 therefore it needs 91 or higher.
The reason you can run 87 on some B18C1's is the knock sensor which will retard the timing to prevent the knock.

B19CivicHB

Alright, Ill be running 12.5:1 in my JDM GSR engine... ill be using 94 octane pump gas, good tuning and a daily prayer to stop detonation. Does higher comp along with higher octane promote or demote fuel efficiency\emissions?

-Nick-

Edit: Good info Gabe


[Modified by B19CivicHB, 6:38 PM 7/2/2002]

g_man80

Since you guys know what you are talking about: with turbo charged appl. you need to run higher octane b/c of the increased pressure (forced air, not vacume) even with low compression pistons, correct?

kane2g

when boosted, you can have high compression pistons, but need to use higher octane. Thats why lower compression is used. But when you increase the boost, make sure you add more fuel too.

93SSPHatch

I guess I might as well get my gas question in this thread. . .

I have a stock 93 Civic CX motor (D15B5) and the engine is pinging at high RPM's in 3rd and up gears. It also pings really bad when I charge up hills.

My local performance shop recommended that I start using 91 octane, instead of the 87 that I was using previously. I switched the octane to the higher grade, and I still hear the pinging/knocking .

Should I switch back to the 87, since the 91 didn't solve any of the pinging problems?

What else could cause this annoying pinging. . .i've changed my plugs, dist. cap/rotor.

Thanks

93SSPHatch

TTT. . .I hope I can get an answer ^ ^ ^




[Modified by 93SSPHatch, 11:26 PM 7/8/2002]

Spade

The pinging could be other things.....i.e. Damage. Is the engine stock?
When is the last time you had the fuel system cleaned.
Carbon build up over time is what i am thinking has gone and raised your compression......it happens.

N-E-Way, service shops do really great fuel system cleaning for about 75 bux.