CLoNE

I'm lost on this? Dose 89 octane gas burn faster and hoter than 92?
or is it the higher the octane the cooler and slower it burns?
Is this rule for gasoline only?

Is not methanol a slower,cooler burning fuel? then gasoline?

What about Alcohol? Is this a slower-cooler or faster-hoter burning fuel,then the other two?

Or do I have this all messed up?

Please say (if you know,for sure) in layman's terms. :confused:

Q1KSLVR

Actually, octane has to do with the speed of the burn. A lower octane will burn quicker but with less of an explosion. The computer sees the lack of octane and opens the injectors longer. This means more is needed to do the same job resulting in less gas mileage and less power.

Now you are getting into racing fuels. They are designed for very high compression and forced air induction engines made to go fast and shut off. I'm not the expert on alt. fuels, just that they will melt your s**t if you use them in your street car. :thumbs:

CLoNE

Actually, octane has to do with the speed of the burn. A lower octane will burn quicker but with less of an explosion. The computer sees the lack of octane and opens the injectors longer. This means more is needed to do the same job resulting in less gas mileage and less power.


Thanks (Q1KSLVR) so lower octane burns quicker and cooler, and a higher octane burns slower and hoter.

well thanks again, my friend and I were both right,kinda.
:seeya


[Modified by CLoNE, 1:32 PM 10/3/2003]

efweber

I have an '84 Corvette with 183K miles. The engine has 60K on it. When I bought it it backfired and missed pretty frequently. I always filled the tank with 91 or 93 octane gas. My mechanic told me the intake manifold gasket needed to be replaced, so I had that done. When I got the car back, it ran better, but still missed a little once in a while. In the meantime, I saw Gordon Killebrew at Carlisle. He said there was no need for the high test gas, so I switched to mid-octane. Since the switch, I have had no problems with missing or backfiring. Anyone got any theories?

Nathan Plemons

This topic has been beat to death, just search the archives. The short of it is that you actually want to run the LOWEST octane gas that you can run full spark advance with. Running a higher octane than you need costs you money, and performance.

CLoNE

So how dose your post help me in any way.You did not answer the question at all. Only bitch about it.

WHAT BURNS FASTER,SLOWER,COOLER,HOTER? Do you understand?


[Modified by CLoNE, 10:54 PM 10/3/2003]

mitymek

"This topic has been beat to death, just search the archives. The short of it is that you actually want to run the LOWEST octane gas that you can run full spark advance with. Running a higher octane than you need costs you money, and performance."
:iagree:
your question was also answered.
higher octane fuel is used when a slower burn is needed to prevent pinging/knock which your knock sensor picks up and signals resulting in timing retard.
sooo,if your question is relative to a c4 vette,what you get from this info is:hook up a scan tool and run the lowest octane gas you can run without triggering a knock sensor event.
(if your question is not c4 vette relative your on the wrong forum :p: )

might wanna try over in tech and performance for your race gas question.



[Modified by mitymek, 8:32 PM 10/3/2003]

CLoNE

Lets beat around a bush.So higher octane burns slow, is it hotter?
And NO I don't think the qustion was or is answered yet.Totally
96 LT4 coupe (clone)
If you don't know, why make a post telling me to search the archives,WHEN YOU CAN JUST MOVE ON.
Funny how some will make a post and NOT a answer or only haft of one?
I must have pissed someone off?Damm some of you write like I'm wineing about the wave. :lol:

Thanks quick silver the only + post yet. :cool:


[Modified by CLoNE, 12:56 AM 10/4/2003]

JCAIRE2

Lower octane = faster burn
Higher octane = slower burn

Couldn't tell you about hotter or cooler. I would imagine a faster burn would be hotter. :confused: What does the relative heat of combustion have to do with what you want to know?

Nathan Plemons

Do you have any proof of this? Why does the same amount of high octane fuel create a richer air / fuel ratio?

Essentially you are saying that there is more "mass" of fuel for any given volume with high octane which is simply not the case. If you take an engine that runs on a low compression ratio, say 8.5:1 and hold everything constant you will see an interesting problem. The 8.5:1 motor can run full timing advance on 87 octane. If you substitute in 93 and hold everything constant the engine will make less power. Why? The higher octane fuel burns slower, less violently if you will. This means that the piston is actually pulling away from the explosion rather than the explosion pushing on the piston, this is also a cooler burn.

If you take the same amount of two fuels and under the same conditions one of which burns cooler you can draw a very important conclusion. The reason why one is less violent is because there is less energy for any given amount to be released.

The power from your engine comes from compression. The higher the compression ratio, the more powerful the explosion will be. Higher octane fuels are LESS powerful, but since they allow higher compression the benefit outweighs the loss. If the engine can not increase compression or timing by running high octane it will only cost you power to run it. Also, since the engine is running at it's capabilities yet the explosion is less powerful you will also see a decrease in gas mileage. Every explosion will release less energy, which means that less work can be done for any amount of fuel.

Run back to back dyno's with 110 octane fuel vs 93. You'll loose power on a street driven car.

For the best engine efficiency you want to run the absolute lowest octane rating that allows you to run full spark advance. That will be the fuel that creates the most power per unit. If you run higher octane fuel you will essentially be running a less potent fuel which means that for any given amount of work you will have to burn more fuel.

Higher octane fuels only give you more power if your engine can't run at it's full capabilities on a low octane fuel, otherwise they cost you power. That's a fact which cannot be disputed.


[Modified by Nathan Plemons, 11:39 AM 10/6/2003]

SurfnSun

I can see both sides of the arguement...and Im stumped

Looks to me like the reasoning would be b/c higher octane fuels will expel more unburned gases causing the O2 sensor to read more rich?

:confused: :confused:

Either way one thing remains unchanged....running too high of octane is a waste of money and detremental to performance.

Q1KSLVR

No. With fuel injection, low octane gives less power and fuel efficiency, and higher octane gives more power with higher efficiency.

There are no constants in a computer controlled engine when it comes to mixture air/fuel ratio or timing. The computer will constantly change the outputs by what it receives from it's inputs.

Nat, buddy, your not getting something. I think you are digging too deep into it.

I don't know what a "Helpdesk Tech." is, but my 19 years as an automotive tech means I know what I'm talking about. :thumbs:

Nathan Plemons

Apparently not. Just because you are certified doesn't mean you are qualified. Rather than just say it's correct because you say so, why don't you get some facts to back it up. You can't build a rational argument so you result to the old "I'm certified, I must be right" stance. Doesn't hold much water.

I'm not trying to call you stupid here, quite the contrary. I keep trying to explain it in such a way that you'll "get it" so you won't regret it. What's worse, a computer tech (me) who would happen to be wrong, or a 19 automotive veteran (you) who would be wrong. I know it's hard to comprehend that you might be misinformed, but if you are incorrect, and you actively spread incorrect knowledge it looks bad on you.

If I screw up an automotive answer every once in a while, it's no big deal, that's not my job and I don't claim to know everything. If you claim to know it all and you give a wrong answer it makes you look really bad.

The fuel injection argument is completely bogus. An engine works on the same principal be it fuel injection or a carb. Sure the engine can adjust for a wider variety of variables with fuel injection, but at it's core that doesn't mean that you are going to magically make more power by running a higher octane fuel than you need.

Honestly now, sit back, take an open mind and re-read what I have to say. It really makes sense and there are plenty of people out there to back it up. Also consider one more thing. If every new car made is fuel injected, and the EPA is getting stricter on fuel economy, why would they not mandate high octane gasoline only? Why would places such as California who are so strict about emissions only allow 91 octane at the majority of gas stations? Why to places of higher elevations such as Colorado have much lower octane fuels? Could it be that the lower atmospheric pressure requires a lower octane fuel for detonation resistance? What a concept.

mitymek

my butt dyno reports no difference between 87 and 91 octane fuel.
my mpg info reports 22 with 87 and 20 mpg is tops with 91 octane.
tested this 3 times over the summer.
although i find all the submitted theories very interesting,i am forced to stick with Gordon Hildebrands recommendation of low octane unless the computers pulling timing.
i've logged 500 miles with a monitor 4000 enhanced diagnostics tool on the passenger seat and never recorded any knock sensor event or timing retard.
this is going to be different for altitude and ambient temp but for where im at on the planet and the temps i run in-works for me.
im talking street use here.
drag racing all day could be a different story altogether.wouldnt surprise me if timing retard occured after 3 or 4 w.o.t. runs on a warm day with 87 octane fuel.
would be nice if someone had dyno or track results using different fuels.

1990CORVETTE

Here you go: Put gas in that SOB and drive it down the road,,,,,, if we are worried about 2 or 4 ratings of octane,, we got prob's.... No matter what kind of gas we put in our cars they will run like a raped ape........ FAST
:boxing :seeya :flag :cool: :steering: :auto: :hurray:

mitymek

:iagree: :thumbs:

Yello95

[QUOTE]Here you go: Put gas in that SOB and drive it down the road,,,,,, if we are worried about 2 or 4 ratings of octane,, we got prob's.... No matter what kind of gas we put in our cars they will run like a raped ape........ FAST


:lol: