octane argument

[absolom]

a car will make the MOST power on the LOWEST octane it can run WITHOUT pinging/detonating

true or false

in other words, say a car runs perfectly fine with no detonation on 93, putting 118 alone with no other changes will NOT boost performance...

correct?

[kamaroman68]

Based on what i learned along time ago yes that is correct. to see the benefits of the increased octane you would need to bump / advance the timing. chris

[EFI69Cam]

The slower burn rate of the 118 gas might even hurt power.

Advancing timing can go only so far, too much advance and the piston is working against the expanding fuel air charge no matter how controlled a burn it is.

[absolom]

The slower burn rate of the 118 gas might even hurt power.

Advancing timing can go only so far, too much advance and the piston is working against the expanding fuel air charge no matter how controlled a burn it is.

yeah, that's exactly what i'm saying

without any other changes, going to higher octane is more likely to hurt power, probably not a whole lot, but a little bit

[Fuelie Fan]

Just so you know, octane and burn rate are not intrinsically linked. Some higher octane fuels burn slower, but some burn faster as well.

[72NovaSS]

if the engine is tuned for the octane then its all good. if you were to put in the 118 octane on a car that has a tune for 93 then yes it will hinder performance.

[72NovaSS]

if youre thinking about putting the 118 in the cobra engine it should do fine with a tune! i know guys that will only run race gas in their daily driver terminators!

[EFI69Cam]

Just so you know, octane and burn rate are not intrinsically linked. Some higher octane fuels burn slower, but some burn faster as well.

Strictly speaking this is true. It would take more research than I want to do to prove it conclusivly, but "octane" as its used now is not an indication of how much octane in in the fuel, but a measure of its resistance to pre-detonation. This resistance usually comes from a slower burn.

What goes on inside a combustion chamber is so complex that it cannot be modeled accurately, chaos theory is the only mathematic model for it.

I think for the sake of the original assertion that more "octane" than what is required to avoid detonation and ping is at best a waste, that octane and burn rate can be interchanged.

[tumper93]

GM tells us now that if your vehicle states to run 87 octane and you run a high octane fuel you will actually be emitting more pollutants, along with possible degraded performance, because the compression ratio along with the timing is not enough to fully burn the fuel within the combustion chambers

[jbone]

I was told that certain motors such as the LS1 and others were capable of adjusting timing themselves "to a certain degree" based on the level of octane detected??? Is this true?

[silver69camaro]

I was told that certain motors such as the LS1 and others were capable of adjusting timing themselves "to a certain degree" based on the level of octane detected??? Is this true?

The computer doesn't detect the octane, but will retard the timing based on a "hit" from the knock sensors. If it detects detonation (say from a lower octane fuel), it will retard the timing to eliminate it.

[David Pozzi]

I moved this thread to the Engine section. It's a better fit.
David

[jbone]

The computer doesn't detect the octane, but will retard the timing based on a "hit" from the knock sensors. If it detects detonation (say from a lower octane fuel), it will retard the timing to eliminate it.

I over heard a conversation that "coil-on-plug" (or something like that) alowed the motor to recognize the type of fuel........So there is no such thing as any engine advancing timing for race fuel correct? .......again I have no idea about this stuff

[LS6 Tommy]

Almost all, if not all, OBDII engines will retard timing based on detonation sensors. AFAIK, none of them will "read" octane and increase timing. Multiple fuel engines somehow "ID" the fuel being used and adjust accordingly.

Tommy

[68sixspeed]

Give it a 'true' for most cases- on my old motor I lost 2-2.5mph at the dragstrip by changing from 93 octane to 100 octane, even with a 10:1 motor. I tried jetting down and still couldn't recover it. I know I didn 't get the a/f mixture optimal on the 100, but it sure didn't impress me.

[Y-TRY]

All of this rings true BUT.. there was a magazine test a few years back that seemed to prove the exact opposite. I tried to write the with "WTF?" but never saw a response.

They ran a pump motor on high octane and gained power. The magazine guys even seemed completely puzzled. It seems crazy, but it's the last time I saw any back-to-back test published and it contradicted everything I thought I knew of octane.

[Adam's 55 Chevy]

All you will do is waste money on fuel you don't need. If your car needs 106 octane 110 may be a buffer but 116 will just be lost $$$.