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Old 04-11-03, 11:45 AM   #1
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What does Lean and Rich really mean?

I have a friend that says lean and rich is the ratio of oil and air or fuel or something.

Now, I've always thought it's the air/fuel ratio but this guy does know more than me about cars so just thought I would clear it up.

And sorry if this has been asked before but seaching turns up some poop and various crap but not any info.
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Old 04-11-03, 11:50 AM   #2
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its the air fuel mixture. rich means the mix have more gas, lean is more air.
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Old 04-11-03, 11:51 AM   #3
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To run lean is to run an a/f (air-fuel) mixture that contains too much air and not enough fuel. Running rich is just the opposite, too much fuel and not enough air. Of course, when I say 'not enough' of one or the other, that's based on what the car wants to run at peak efficiency.

It has nothing to do with oil.
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Old 04-11-03, 12:14 PM   #4
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See?!!! That's what I thought! He's full of crap!
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Old 04-11-03, 04:51 PM   #5
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Lean and rich are both things I am not. I don't know if that helps at all
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Old 04-11-03, 06:31 PM   #6
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Quote:
Originally posted by MosesX605
To run lean is to run an a/f (air-fuel) mixture that contains too much air and not enough fuel. Running rich is just the opposite, too much fuel and not enough air. Of course, when I say 'not enough' of one or the other, that's based on what the car wants to run at peak efficiency.

It has nothing to do with oil.
There is an ideal mixture of fuel and air which when combusted would consume all of the oxygen in the air and all of the carbon in the fuel to make H2O and CO2. There would be no left over Hs, Os and Cs. This is referred to as the stoicometric ratio. This is the ratio of air to fuel where an engine runs most fuel efficiently and still functions correctly.

Any ratio of air to fuel (air/fuel) that is larger than this ratio means that there is more air than needed for this ideal combustion mixture. Any ratio smaller means that there is more fuel than needed for the ideal combustion.

This ratio is different depending on the fuel. Also, no combustion is ideal due to many factors, so even at the stoicometric ratio, there will still in reality be non-ideal exhaust products.
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Old 04-11-03, 09:50 PM   #7
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The stoicometric ratio is based on what's the best ratio the CAT can convert those bad gasses into H20 and CO2 I think the ratio was 14.7 parts air and 1 part fuel... some say 15 to 1 but whose counting...
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Old 04-11-03, 11:38 PM   #8
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Quote:
Originally posted by MRGSL-SE
The stoicometric ratio is based on what's the best ratio the CAT can convert those bad gasses into H20 and CO2 I think the ratio was 14.7 parts air and 1 part fuel... some say 15 to 1 but whose counting...
its 14.1 to 1 i thought. i know i read somewhere someone actually proved on a dyno rotaries run better with the mixture in the 12's. i think like 12.9 to 1. dont hold me against that, but can anyone else varrify that?
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Old 04-12-03, 01:27 AM   #9
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Oh of course!

Yes, quite!

I do fancy a intelectual conversation now and again.

Who am I kidding? I have no idea what you guys are talking about.
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Old 04-12-03, 01:31 AM   #10
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I always believed that it was in the 14's for an n/a engine and mid 12's to mid 13's for a turbo car. I never did know why it would be so different and frankly it doesn't matter too much to me. My car sits pretty at 14.7 almost all the time (I love having a stand alone ems ).
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Old 04-12-03, 04:09 PM   #11
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Quote:
Originally posted by MRGSL-SE
The stoicometric ratio is based on what's the best ratio the CAT can convert those bad gasses into H20 and CO2 I think the ratio was 14.7 parts air and 1 part fuel... some say 15 to 1 but whose counting...
No, this is wrong, the stoicometric ratio isn't influenced at all by the catalytic converter, my previous post explains exactly what it is.

For gasoline, it's 14.7:1 air:fuel on a mass basis. This doesn't have anything to do with the aspiration of the car, tubo or natural. It's dependent on the hydrocarbon fuel, so gasoline is different from propane or hexane or diesel.

Most engines and especialy rotories run rich. The combustion of a rich mixture is cooler than a lean mixture so it's safer for the engine to be rich. Also, the maximum power of an engine is rich of stoic. For these reasons you will see that people tune to a/f ratios in the 11-13 range.

Under cruising, where the engine is at a constant speed and a fairly low load is the only time when you want your car to be running near stoicometric.

Last edited by purple82; 04-12-03 at 04:14 PM.
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Old 04-12-03, 04:09 PM
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