Octane
Thread Starter
TECH Veteran
iTrader: (7)
Joined: Aug 2004
Posts: 4,996
Likes: 1
From: Southeastern IL
Octane The practical application of the octane rating in fuel seems to be a bit misunderstood by many. I don't know how many times I hear someone say they want to put 100 octane gas (or whatever) in their car to make it "go faster." As I understand it, that is not how things work.
I started this thread -- which has a significant chance of dying due to lack of interest -- as an open discussion about the practical application of octane ratings in gasoline. Honestly, I'd rather not get into ethanol as there are plenty of good threads about that.
I have a couple general questions to which I already have a pretty good idea I know the answers.
I've read that using lower octane fuel (87/89) in our engines makes them less fuel efficient than running higher octane (91/93). I think it's this ideology that has lead some to post that running 87/89 doesn't save money at the pump. Is this true?
I've read that running higher octane fuel produces more heat. Is this true?
Thanks!
I started this thread -- which has a significant chance of dying due to lack of interest -- as an open discussion about the practical application of octane ratings in gasoline. Honestly, I'd rather not get into ethanol as there are plenty of good threads about that.
I have a couple general questions to which I already have a pretty good idea I know the answers.
I've read that using lower octane fuel (87/89) in our engines makes them less fuel efficient than running higher octane (91/93). I think it's this ideology that has lead some to post that running 87/89 doesn't save money at the pump. Is this true?
I've read that running higher octane fuel produces more heat. Is this true?
Thanks!
TECH Resident
Joined: Apr 2008
Posts: 834
Likes: 12
From: Right here, right now!
5.5 million posts! Is that for real? 
The published info I had on this is long gone but I do recall that running fuel with an octane rating much above what is needed to prevent knock in "the" optimised engine of choice is not just a waste of time but also can see a loss of power as less energy is available from fuel (gasoline vs gasoline as the example) of higher octane ratings.
IIRC this is due to the higher octane fuel requiring more heat to fully vaporise which robs the combustion process of heat.
Of course the trade off gained by higher comp and higher octane when NEEDED does outweigh the loss of power due to a lower energy fuel.
BUT: this is all by memory and the details are vague now and have read the opposite elsewhere since so not really sure of what is true/correct.
But it is an excellent question!!!
The published info I had on this is long gone but I do recall that running fuel with an octane rating much above what is needed to prevent knock in "the" optimised engine of choice is not just a waste of time but also can see a loss of power as less energy is available from fuel (gasoline vs gasoline as the example) of higher octane ratings.
IIRC this is due to the higher octane fuel requiring more heat to fully vaporise which robs the combustion process of heat.
Of course the trade off gained by higher comp and higher octane when NEEDED does outweigh the loss of power due to a lower energy fuel.
BUT: this is all by memory and the details are vague now and have read the opposite elsewhere since so not really sure of what is true/correct.
But it is an excellent question!!!
Last edited by rsz288; May 5, 2010 at 04:02 AM. Reason: Editing........ :)
The practical application of the octane rating in fuel seems to be a bit misunderstood by many. I don't know how many times I hear someone say they want to put 100 octane gas (or whatever) in their car to make it "go faster." As I understand it, that is not how things work.
I started this thread -- which has a significant chance of dying due to lack of interest -- as an open discussion about the practical application of octane ratings in gasoline. Honestly, I'd rather not get into ethanol as there are plenty of good threads about that.
I have a couple general questions to which I already have a pretty good idea I know the answers.
I've read that using lower octane fuel (87/89) in our engines makes them less fuel efficient than running higher octane (91/93). I think it's this ideology that has lead some to post that running 87/89 doesn't save money at the pump. Is this true?
I've read that running higher octane fuel produces more heat. Is this true?
Thanks!
I started this thread -- which has a significant chance of dying due to lack of interest -- as an open discussion about the practical application of octane ratings in gasoline. Honestly, I'd rather not get into ethanol as there are plenty of good threads about that.
I have a couple general questions to which I already have a pretty good idea I know the answers.
I've read that using lower octane fuel (87/89) in our engines makes them less fuel efficient than running higher octane (91/93). I think it's this ideology that has lead some to post that running 87/89 doesn't save money at the pump. Is this true?
I've read that running higher octane fuel produces more heat. Is this true?
Thanks!
At higher temperatures the fuel is burned more efficiently. So, while it’s true that the higher-octane fuel does not posses any more energy than low octane fuel, the increased octane allows the extraction of more of the potential energy that has always been there. Conversely, lower compression ration engines utilize a little less of the fuel energy potential (2-4% reduction) but there is also less heat generated in the combustion process.
What I get form that is there is more heat created in the burning of high octane fuel. It makes sense because it takes more energy to get a higher octane fuel to burn.
These are just my opinions and may be entirely wrong, but they are opinions nonetheless.
