High octane gas burns slower,…

Posted: Fri Oct 13, 2006 11:31 pm

…and this is how it prevents knock, detonation, and pre-ignition. This is a sort of “conventional wisdom” one can read on many forums these days, and people seem to reach a consensus on this, and this saying goes as common knowledge without questioning by others. Like “when something falls, it falls down”.

From combustion researcher point of view gas/air mixture burning speed has no relation whatsoever to particular gasoline octane rating and, therefore, does not affect its ability to prevent abnormal combustion. Different gasolines can burn slightly slower or slightly faster depending on the exact components used.

Detonation is an uncontrolled explosion, and its speed is 10s if not 100s times faster than any normal fuel burning speed. The difference between gas oven normal burning and its explosion in case something bad happened can give you an idea of the difference between normal combustion in engine and detonation. This is nowhere near the range of burning speeds different fuels have.

Member Joined: Nov 15, 2006 Posts: 18

Put 87 in a turbocharged car tuned for 93, and see if it preformce the same. I am pretty sure you'll change your mind.
EX: Friends chipped GTI, tuned for 91-94 octane, one day we put 87 in it, check engine light was on, saying there is detonation, and car run like complete poop. Think he just got the magical 4 gallons of bad fuel? I doubt it. Never happend with 93, maybe you should do more research as insulting as this sounds, I really don't mean to question your knowledge, but from what I read it doesn't seem like you know all that much about car tunning. From reading your original post, it sound as if a drag car tuned for 110 gas. will run just about the same on 87, did I misunderstand something here?

Posted: Thu Nov 16, 2006 1:57 am

I see, looks like bad wording on my side, sorry. When one goes to do myth busting, he should be more precise. Very Happy

I did not mean you should put low octane fuel into the engine that needs high octane, it's a sure way to ruin your engine.
I meant that fuel octane rating does not show how slow or fast fuel burns under normal conditions, it has nothing to do with that speed. I can try to elaborate on this tomorrow...

Posted: Fri Nov 17, 2006 10:41 pm

Ok, let me try to re-phrase it here. Wink

People think that octane rating shows how slow gas will burn in the engine. The higher the rating, the slower it will burn.

I’m telling that octane rating and burning speed are two completely unrelated parameters. Gas with high octane rating can burn faster or slower than gas with low octane rating. And this speed does not matter at all as long as it is within gas specifications.

Let me know if this does not clarify the issue, please.

New member Joined: May 09, 2012 Posts: 4

I think Misha, what your getting at is that some consumers are buying high octane gas with the "it burns slower' mentality thinking that slower burning gas is Somehow saving them fuel.. Ie it lasts longer.

Or is it that Performance guys who know that their high compression engine needs some kind of protection against pre ignition/detonation.. try to incorrectly explain high octanes welcomed resistance to pre-ignition.. as 'it burns slower'

How ever it works, I like not having melted pistons every 100k miles.

Posted: Fri May 11, 2012 9:20 pm

Hi MonzaMan, nice to meet you and welcome to Fun and Safe Driving Smile

This was written like 5 years ago, so I don't remember exactly what prompted it - though I doubt it was about saving gas. Mostly likely it was related to discussions on hondacivicforums.com, and those teens care much more about performance than savings Smile