I am curious if there is any correlation between octane and likelihood of flooding. There are a number of posts indicating that high octane gas yields a rough idle and that high octane gas is slower to ignite in normal operating conditions (decreasing the chances of pinging). Is there any reason to believe that high octane would also increase the likelihood of flooding?

 

My guess is no. I was not aware that high octane gas is "slower to ignite". In fact, I'm pretty sure it isn't "slower to ignite". High octane gas can withstand more compression than lower octane, but given a spark, will ignite just as quickly as low octane. You'll have to wait for someone else to post if you need a more technical answer.

 

Been using 92/93 octane here for over 1000 miles and not had a problem with flooding or rough idle. I do follow the manual in regards to letting the car warm up if only going a short distance.

 

Been using 87 octane. No difference in starting or performance. Have never flooded on high or low octane. The rotory idles a little rough because the car is so smooth off idle Mazda did not have to employ a counter balancer like most cars. The rough idle just adds to the charactor and mystique of the car. IHMO

 

The ' My Mazda web site ' recommends using the lowest octane within the octane range listed in the manual. Manual recommends 87 to 93 octane. Thats why I burn 87. The car runs the same and I save at the pump.

 

He's right about the higher the octane, the harder it is to ignite. That's why high compression and high heat motors need higher octane fuels to prevent pre-ignition.

I however am pretty sure that octane levels will have nothing to do with flooding or prevention thereof.

 

It withstands more compression...I stated that. If by withstanding more compression you mean harder to ignite, then sure. But if you take a flame to either octane fuels, they both ignite just as quickly. In other words, one is no more flammable than the other!

 

No, it really does burn slower and is harder to ignite. Octane rating of a fuel is the measurement of the fuel's resistance to ignite. That's why when people with normal cars put high octane fuel in, they can actually see a decrease in performance and fuel economy. Taking a match to a pools of gas of varying octanes isn't a precise enough test to observe the differences though... we're talking about small differences that under the heat of compression will become apparent.

 

Tell me more.......

If it's 'harder to ignite', maybe we could fire the sparkplugs twice?....make sure, in case it doesn't 'catch' the first time......

It burns slower? How does this theory fit in a 9000 rpm scenario?

If you put high octane in a regular car you will get worse fuel economy? Please explain, I'm keen to hear all about that one....

Please, fill us in with the details, this is priceless stuff, let me get a pen to write this all down......

Sorry, my name is Doc, and I'm a 'sarcast-alholic'.......I been clean for two weeks.....
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doc

 

Yeah, but it would be cool to watch! :D

Anyone have a pool or two they'd like to volunteer to science?

-Eric

 

Ok oh sarcastic one... then everything I've read over the years is wrong. You're going to tell me that a fuel's octane rating is /not/ a measurement of it's resistance to ignite under compression...?

I'll admit the term 'harder to ignite' isn't the most accurate, but I eagerly await your definition of what effect different octane levels have on fuel... pen in hand.

 

apparently many racing sites agree with you, higher octane does burn slower. i'm learning something new every day! I liked this site's explanation:

not this one, but this one

 

oh man that reminds me of an experience i had with a campfire and a tank of gas. a friend of mine's idiot brother had a plastic gasoline container and was pouring gasoline trails and igniting them. Well, the container was almost empty when he lost his grip on it and it fell into one of the fire trails. the opening caught fire and everyone instinctively starts hauling *** away from the container, except for my buddy. he runs over and stomps the thing as hard as he can in an attempt to put out the fire. instead, he ends up launching a 30 ft fireball. the crowd oooo's and aaaaah's for a minute. so then he stomped it a few more times to let out some more fireballs. very neat, very dangerous, but very cool to watch.

 

That site's info is similar to how I learned it... although I know there are other factors involved with the fuel chemistry when you start talking about race gas vs. pump gas. I tried to read up on this stuff when I was modding my Miata by advancing the ignition timing many years ago. Advancing it too much induced pre-ignition, which was resolved by running 93 octane since I was in SoFlorida at the time. When I moved north, I was able to drop to 89-91 octane and add a couple more degrees of ignition advance because of the cooler, drier air.

 

I have two neighbors with above-ground eyesores, I mean pools, that I'd gladly volunteer

 

LOL

-Eric

 

my owner's manual say use at least 90 octane. Since that is an octane that is not available, I use the 93 octane.

 

One more wrinkle. Take an engine that needs 91 octane. If you put 87 octane in it will ping. However with the magic of modern technology, the engine computer detects this pinging and adjusts things (richness, timing etc) to prevent pinging. The engine is saved, but he new anti-ping parameters cause a loss of horsepower. According to the manual the Rx8 is such an engine. I haven't tried cheap gas in the Rx8, but the power loss in my wife's 626 can actually be felt behind the wheel. Even at today's inflated gas prices, 87 only saves like $2 a fillup.
--Dave.

 

Hmm. I can't tell any difference in power between 87 and 93 octane.