The Importance of Proper Air-Fuel Ratios and Engine Tuning

It's often said that an engine is only as good as its tuning, and one key aspect of tuning is understanding how to balance air-fuel ratios. When an engine is properly tuned, it runs smoothly and efficiently, producing the desired power output. However, if the air-fuel ratio is off, it can lead to a range of problems, including decreased performance, increased emissions, and even engine damage.

One common misconception is that running lean (more air than fuel) will somehow magically improve an engine's performance. Unfortunately, this is not the case. In fact, running lean can have the opposite effect, pulling down combustion temperatures and reducing power output. When an engine is running lean, it's unable to burn all of the oxygen present in the cylinder, which leads to lower combustion temperatures. This can cause a range of problems, including decreased performance, increased emissions, and even engine damage.

So why do people say that an engine is running too lean? The answer lies in knock, or pinging, which occurs when there are multiple combustion fronts within the cylinder. This can happen when the temperature and compression ratios become too high, causing a spark to ignite areas of hot air pockets. Knock can cause significant engine damage and is something that tuners strive to avoid.

To prevent knock, tuners use various strategies, including ignition timing adjustments and changes to the air-fuel ratio. By pulling the air-fuel ratio down, tuners can reduce combustion temperatures and minimize the likelihood of knock. This is particularly important for turbocharged or forced induction engines, which often require a more precise tuning process.

When it comes to maximizing power output, most engines are designed to run rich (more fuel than air). However, even in these situations, running too lean (less fuel than air) can cause problems with combustion temperatures and lead to knock. Conversely, if the engine is tuned too rich (more fuel than necessary), it can lead to reduced performance and increased emissions.

The ideal air-fuel ratio will vary depending on the specific engine design and application. However, for most engines, a ratio of 11-13:1 or 12:1 is considered optimal. At these ratios, the engine is able to burn all of the oxygen present in the cylinder, producing maximum power output while minimizing emissions.

To maximize power output, tuners will often try to find that sweet spot within this rich region. However, if the air-fuel ratio becomes too lean (less than 12:1), temperatures start to rise, and knock can occur. This is why it's so important for tuners to carefully monitor the engine's performance and make adjustments as necessary.

By understanding how to balance air-fuel ratios and proper engine tuning techniques, tuners can optimize their engines for maximum power output while minimizing emissions and reducing the risk of engine damage. Whether you're a seasoned tuner or just starting out, mastering these skills is essential for achieving peak performance from your vehicle.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video we are talking about a common misconception and that is that running an engine lean uh causes it to run hot so you'll often hear people say oh the engine's running too lean as a result it's getting too hot that's why you're having problems occur but running an engine lean actually doesn't cause it to run hot in fact it does the opposite it causes it to run cool now there is some validity to saying oh it's too lean it's going to run hot it's going to have problems which we will get into in this video but ultimately a lean burning engine meaning it's using a lean air fuel ratio will burn cool so just as a quick refresher the ideal or stoichiometric air fuel ratio for gasoline is about 14.7 to one so that is a ratio by mass 14.7 parts of air by mass one part fuel by mass lean is anything greater than that so more air than you can use and you don't have quite enough fuel rich is anything less than 14.7 to 1 meaning you have excess fuel you will not be able to burn all of the fuel so first of all what are the facts what actually happens to combustion temperatures as you change that air fuel ratio and so here we just have a simple plot where we have temperature plotted on the left and then here on the bottom we have the air fuel ratio ranging from about 10 which would be very rich to 20 which would be extremely lean and so they're in the center about 14.71 or just 15 to 1 we've got our ideal air fuel ratio and as you can see uh based on this chart which of course i've drawn uh but it is somewhat accurate is that our peak temperature is going to occur around stoichiometric ideal air fuel ratio that's where you're going to have the highest temperature occur for combustion and part of why you can tell is because of nitrogen oxide emissions now nitrogen oxide emissions only occur when you have very high cylinder temperatures that's what you need in order for that reaction to occur to have that nitrogen and oxygen bond together and so in this reaction you will see that it peaks around stoichiometric air fuel ratios and it peaks wherever temperature is the hottest and so you will see that temperature will decrease as you get richer air fuel mixtures you will see that temperature will get lower as well as you get into leaner air fuel mixtures and you will see nitrogen oxide emissions correlating with that so you know this may say that oh if we want to reduce nitrogen oxide emissions we can go rich or lean that is true generally speaking if you go rich though that means you're dumping in more fuel and by dumping in more fuel you're going to add additional carbon emissions you've got more hydrocarbons in the equation so more hydrocarbons going out the exhaust now why does an engine running rich or running lean cause combustion temperatures to drop any idiot can draw a graph and say here it is this is why it's true but it's more important to understand is that actually true and why is it true so looking at some different cylinders here each one of these we've got a different scenario going on so ideally you have that 14.71 ratio so you have the perfect amount of fuel the perfect amount of air all of that air and fuel burns a rich mixture is going to have a bit of excess fuel that's what i've drawn here in purple and then a lean mixture will have a bit of excess air you're not able to burn all of the oxygen in it so in the ideal world great 14.1 sounds awesome you could make the perfect amount of power but unfortunately not all of that air actually gets used in this ideal mixture you have different ratios air fuel ratios occurring within that cylinder and not all of the fuel and air is burned up so unfortunately you're not making peak power if you are actually at a 14.7 to 1 air fuel ratio so what you will do is you will reduce that air fuel ratio you will run rich inject extra fuel and that ensures that you use up absolutely all of the oxygen within that cylinder in order to make the most amount of power possible so if you're running rich that means you're able to burn all of that oxygen and make more power however that also means that there's excess fuel sitting in that combustion chamber and that excess fuel changes from a liquid to a gas and during that phase change it brings down the temperature within that cylinder so your combustion temperatures go down as you start to inject more fuel and that fuel undergoes that phase change where it goes from liquid to a gas and in doing so cools the internal temperatures of that cylinder so why does it then happen also why do temperatures also decrease as you start to lean out that mixture well going back to our little drawing right here where you have the amount of fuel injected it's not quite enough to burn all the air in the cylinder so you've got this lighter blue color which is all the air that you can burn and then you've got that darker blue and that's that excess air and so you've just got excess air sitting in there that you can't actually use for combustion if you were to able to burn all of it you would get higher temperatures within that cylinder it's a very similar strategy to egr so exhaust gas regulation is taking exhaust gases that have already gone through combustion routing them back into the cylinder and that inert gas isn't doing anything it's not adding any power it's not improving your combustion temperatures in fact it's pulling it down and so by putting in that egr or just by adding more air you're not able to burn all that air and your combustion temperatures drop so whether it's egr or running lean that means bringing down your combustion temperatures and as a result of bringing down your combustion temperatures you can reduce your nitrogen oxide emissions so that's what egr is used for egr is used in order to reduce your nitrogen oxide emissions by using exhaust gas a similar thing can be done by simply injecting more air or just not enough fuel and running lean okay so then why do people say your engine is running too lean it's running too hot as a result you're going to have damage you don't want to run it that lean well this kind of gets into the tuning of the engine and so you know knock is certainly something that you want to prevent so as your piston is coming up compressing that air fuel mixture your spark plug fires it starts to travel but if the compression alone within that cylinder and the temperature alone within that cylinder is able to ignite another area then you've got another pocket of combustion that starts you've got two combating flame fronts and you can have quite a bit of engine damage as a result of it so knock is not a good thing and it results when you start to have really high combustion temperatures once you start rising these cylinder temperatures you get a greater likelihood for it occurring because that temperature is able to combust those hot areas and so what you want to avoid is a knock of course and you do so through multiple strategies one strategy is using ignition timing another strategy is using air fuel ratio which we're discussing in this video so by pulling your air fuel ratios down you can have cooler combustion and by having cooler combustion you can avoid running into knock so here's kind of where this thing comes from let's say you put your car on the dyno and you're tuning it you're trying to maximize power and that peak power is going to occur you know somewhere around 11 to 13 to 1 air fuel ratios maybe around 12 to 1 as an air fuel ratio and it's going to vary a little bit engine to engine but somewhere in that ratio is where you're able to burn up all of that oxygen and make good power so no matter what especially if this is a turbocharged or forced induction engine you're going to be running rich when you're at wide open throttle when you're trying to make maximum power you're for sure going to be running the engine rich and that's to pull those temperatures down and to maximize power so as you start to get less rich below we're still below you know that stoichiometric that ideal air fuel ratio then temperatures start to rise so if you're running a turbocharged engine with an air fuel ratio of 14 to 1 1401 is still technically a rich air fuel mixture but your temperatures are going to rise up enough that you could start to run into some knock problems and so this is kind of where that saying comes from you know running lean runs hot that kills your engine but reality is you know you're never going to actually be running lean when you're trying to maximize power you're going to be somewhere in this rich region and if you're running less rich which would you know like be the technical way to describe it dude you're running too not enough uh you're not running rich enough is like the you know way of of being accurate about it i don't care about the like you know what do you call it um but technically speaking running lean will drop temperatures and i think that's caused a bit of confusion in some of my videos i've started talking about how you know you can run lean in order to reduce nitrogen oxide emissions and a lot of people have said wait a minute but running lean runs hot and i think it comes from this where you know let's say you're getting your engine tuned you're not running rich enough you're still running rich but not rich enough then you're going to start to run into these problems with knock and having you know engine problems because the engine is running too hot at these uh less rich areas versus if you were somewhere over here and that happy region you know the the oems are going to be having their engines around that 11 to 12 region for boosted engines to make sure that it's in a very safe spot that you don't have detonation you bring down those combustion temperatures so i believe that's kind of where this comes from of people believing that lean runs hot when in reality lean runs cool and it can be used in certain engines as an advantage to run lean for efficiency purposes and for emissions purposes so if you guys have any questions or comments of course feel free to leave those below and thanks for watchinghello everyone and welcome in this video we are talking about a common misconception and that is that running an engine lean uh causes it to run hot so you'll often hear people say oh the engine's running too lean as a result it's getting too hot that's why you're having problems occur but running an engine lean actually doesn't cause it to run hot in fact it does the opposite it causes it to run cool now there is some validity to saying oh it's too lean it's going to run hot it's going to have problems which we will get into in this video but ultimately a lean burning engine meaning it's using a lean air fuel ratio will burn cool so just as a quick refresher the ideal or stoichiometric air fuel ratio for gasoline is about 14.7 to one so that is a ratio by mass 14.7 parts of air by mass one part fuel by mass lean is anything greater than that so more air than you can use and you don't have quite enough fuel rich is anything less than 14.7 to 1 meaning you have excess fuel you will not be able to burn all of the fuel so first of all what are the facts what actually happens to combustion temperatures as you change that air fuel ratio and so here we just have a simple plot where we have temperature plotted on the left and then here on the bottom we have the air fuel ratio ranging from about 10 which would be very rich to 20 which would be extremely lean and so they're in the center about 14.71 or just 15 to 1 we've got our ideal air fuel ratio and as you can see uh based on this chart which of course i've drawn uh but it is somewhat accurate is that our peak temperature is going to occur around stoichiometric ideal air fuel ratio that's where you're going to have the highest temperature occur for combustion and part of why you can tell is because of nitrogen oxide emissions now nitrogen oxide emissions only occur when you have very high cylinder temperatures that's what you need in order for that reaction to occur to have that nitrogen and oxygen bond together and so in this reaction you will see that it peaks around stoichiometric air fuel ratios and it peaks wherever temperature is the hottest and so you will see that temperature will decrease as you get richer air fuel mixtures you will see that temperature will get lower as well as you get into leaner air fuel mixtures and you will see nitrogen oxide emissions correlating with that so you know this may say that oh if we want to reduce nitrogen oxide emissions we can go rich or lean that is true generally speaking if you go rich though that means you're dumping in more fuel and by dumping in more fuel you're going to add additional carbon emissions you've got more hydrocarbons in the equation so more hydrocarbons going out the exhaust now why does an engine running rich or running lean cause combustion temperatures to drop any idiot can draw a graph and say here it is this is why it's true but it's more important to understand is that actually true and why is it true so looking at some different cylinders here each one of these we've got a different scenario going on so ideally you have that 14.71 ratio so you have the perfect amount of fuel the perfect amount of air all of that air and fuel burns a rich mixture is going to have a bit of excess fuel that's what i've drawn here in purple and then a lean mixture will have a bit of excess air you're not able to burn all of the oxygen in it so in the ideal world great 14.1 sounds awesome you could make the perfect amount of power but unfortunately not all of that air actually gets used in this ideal mixture you have different ratios air fuel ratios occurring within that cylinder and not all of the fuel and air is burned up so unfortunately you're not making peak power if you are actually at a 14.7 to 1 air fuel ratio so what you will do is you will reduce that air fuel ratio you will run rich inject extra fuel and that ensures that you use up absolutely all of the oxygen within that cylinder in order to make the most amount of power possible so if you're running rich that means you're able to burn all of that oxygen and make more power however that also means that there's excess fuel sitting in that combustion chamber and that excess fuel changes from a liquid to a gas and during that phase change it brings down the temperature within that cylinder so your combustion temperatures go down as you start to inject more fuel and that fuel undergoes that phase change where it goes from liquid to a gas and in doing so cools the internal temperatures of that cylinder so why does it then happen also why do temperatures also decrease as you start to lean out that mixture well going back to our little drawing right here where you have the amount of fuel injected it's not quite enough to burn all the air in the cylinder so you've got this lighter blue color which is all the air that you can burn and then you've got that darker blue and that's that excess air and so you've just got excess air sitting in there that you can't actually use for combustion if you were to able to burn all of it you would get higher temperatures within that cylinder it's a very similar strategy to egr so exhaust gas regulation is taking exhaust gases that have already gone through combustion routing them back into the cylinder and that inert gas isn't doing anything it's not adding any power it's not improving your combustion temperatures in fact it's pulling it down and so by putting in that egr or just by adding more air you're not able to burn all that air and your combustion temperatures drop so whether it's egr or running lean that means bringing down your combustion temperatures and as a result of bringing down your combustion temperatures you can reduce your nitrogen oxide emissions so that's what egr is used for egr is used in order to reduce your nitrogen oxide emissions by using exhaust gas a similar thing can be done by simply injecting more air or just not enough fuel and running lean okay so then why do people say your engine is running too lean it's running too hot as a result you're going to have damage you don't want to run it that lean well this kind of gets into the tuning of the engine and so you know knock is certainly something that you want to prevent so as your piston is coming up compressing that air fuel mixture your spark plug fires it starts to travel but if the compression alone within that cylinder and the temperature alone within that cylinder is able to ignite another area then you've got another pocket of combustion that starts you've got two combating flame fronts and you can have quite a bit of engine damage as a result of it so knock is not a good thing and it results when you start to have really high combustion temperatures once you start rising these cylinder temperatures you get a greater likelihood for it occurring because that temperature is able to combust those hot areas and so what you want to avoid is a knock of course and you do so through multiple strategies one strategy is using ignition timing another strategy is using air fuel ratio which we're discussing in this video so by pulling your air fuel ratios down you can have cooler combustion and by having cooler combustion you can avoid running into knock so here's kind of where this thing comes from let's say you put your car on the dyno and you're tuning it you're trying to maximize power and that peak power is going to occur you know somewhere around 11 to 13 to 1 air fuel ratios maybe around 12 to 1 as an air fuel ratio and it's going to vary a little bit engine to engine but somewhere in that ratio is where you're able to burn up all of that oxygen and make good power so no matter what especially if this is a turbocharged or forced induction engine you're going to be running rich when you're at wide open throttle when you're trying to make maximum power you're for sure going to be running the engine rich and that's to pull those temperatures down and to maximize power so as you start to get less rich below we're still below you know that stoichiometric that ideal air fuel ratio then temperatures start to rise so if you're running a turbocharged engine with an air fuel ratio of 14 to 1 1401 is still technically a rich air fuel mixture but your temperatures are going to rise up enough that you could start to run into some knock problems and so this is kind of where that saying comes from you know running lean runs hot that kills your engine but reality is you know you're never going to actually be running lean when you're trying to maximize power you're going to be somewhere in this rich region and if you're running less rich which would you know like be the technical way to describe it dude you're running too not enough uh you're not running rich enough is like the you know way of of being accurate about it i don't care about the like you know what do you call it um but technically speaking running lean will drop temperatures and i think that's caused a bit of confusion in some of my videos i've started talking about how you know you can run lean in order to reduce nitrogen oxide emissions and a lot of people have said wait a minute but running lean runs hot and i think it comes from this where you know let's say you're getting your engine tuned you're not running rich enough you're still running rich but not rich enough then you're going to start to run into these problems with knock and having you know engine problems because the engine is running too hot at these uh less rich areas versus if you were somewhere over here and that happy region you know the the oems are going to be having their engines around that 11 to 12 region for boosted engines to make sure that it's in a very safe spot that you don't have detonation you bring down those combustion temperatures so i believe that's kind of where this comes from of people believing that lean runs hot when in reality lean runs cool and it can be used in certain engines as an advantage to run lean for efficiency purposes and for emissions purposes so if you guys have any questions or comments of course feel free to leave those below and thanks for watching\n"