Air Fuel Ratio
06-28-2006, 04:13 PM
#1
Air Fuel Ratio
I think it will be fun to have an open discussion on Air Fuel Ratio, there is allot to be learned and it will help myself and others with the topic.
As I too am learning as I go, here is one interesting fact that I picked up: 14.7:1 is considered perfect AFR due to the fact that it is as close to a 100% burn of the fuel as you can get.
I hope we can keep this on topic and educational. Could be beneficial to all.
16.0:1 LEAN
14.7:1 Stoich / Lamda
12.0:1 Rich
N/A 12.8 - 13.2 Ideal
N/A 12.8 - 13.2 Ideal
Boost 11.8 - 12.2 Ideal
Boost / N20 11.0 - 11.8
As I too am learning as I go, here is one interesting fact that I picked up: 14.7:1 is considered perfect AFR due to the fact that it is as close to a 100% burn of the fuel as you can get.
I hope we can keep this on topic and educational. Could be beneficial to all.
06-28-2006, 04:48 PM
#3
Originally Posted by Sport Side
How much, boost / N2O?
06-28-2006, 04:49 PM
#4
I always saw 14.7 as a perfect emmission scenario. The least amount of nitrogen and hydrocarbons. Nitrogen=ozone killer and hydrocarbon=smog. 14.7 isn't necessarily a complete burn as you mention, just the most acceptable EPA levels.
Different altitudes, areas, and smallest differences in vehicle setups can obviously effect "acceptable" afr's for the performance minded (hence the range you mention), but again striving for 14.7 and you are more enviromentally friendly...not necessarily the best performance or "efficient".
Different altitudes, areas, and smallest differences in vehicle setups can obviously effect "acceptable" afr's for the performance minded (hence the range you mention), but again striving for 14.7 and you are more enviromentally friendly...not necessarily the best performance or "efficient".
06-28-2006, 04:55 PM
#5
Originally Posted by dewmanshu
I always saw 14.7 as a perfect emmission scenario. The least amount of nitrogen and hydrocarbons. Nitrogen=ozone killer and hydrocarbon=smog. 14.7 isn't necessarily a complete burn as you mention, just the most acceptable EPA levels.
Different altitudes, areas, and smallest differences in vehicle setups can obviously effect "acceptable" afr's for the performance minded (hence the range you mention), but again striving for 14.7 and you are more enviromentally friendly...not necessarily the best performance or "efficient".
Different altitudes, areas, and smallest differences in vehicle setups can obviously effect "acceptable" afr's for the performance minded (hence the range you mention), but again striving for 14.7 and you are more enviromentally friendly...not necessarily the best performance or "efficient".
I am open for discussion on this topic, I might learn something.
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Adam Schneider (12-07-2023)
06-28-2006, 08:30 PM
#6
Okay heres one I learned when I first started this treacherous pain in the *** of modding my truck. I used to refer to the O2 sensor as being able to see how rich it is. Technically speaking, the sensor, narrow and wide only measure the amount of oxygen in the exhaust stream. Sounds simple enough, but I betcha alot of people think these sensors can see too much fuel. They don't, they see less oxygen. Hmmmm.
Another important note about BC's AFR ranges is that with all of the diffeent engine components these days, the whole 12.8 to 13.2 for n/a is only attainable recently (within the last 10 years) due to better combustion chambers and better heat efficient materials (aluminum versus' iron heads). Got an IronHead combo, you better stick to a 12.5:1 ratio.
Digging through my tuning "notebook" I have collected over the last couple years, this little piece of info is awesome IMO...
Why so important to me? well in tuning, fine tuning, no need to get all excited about a severe (15 to 16:1) AFR at part throttle when you are in open loop tuning. Just worry once you get near the 85 to 95kpa area of your ve table.
Another important note about BC's AFR ranges is that with all of the diffeent engine components these days, the whole 12.8 to 13.2 for n/a is only attainable recently (within the last 10 years) due to better combustion chambers and better heat efficient materials (aluminum versus' iron heads). Got an IronHead combo, you better stick to a 12.5:1 ratio.
Digging through my tuning "notebook" I have collected over the last couple years, this little piece of info is awesome IMO...
Originally Posted by I don't remember where I got this...its a zeroxed sheet out of a book and highlighted
When it comes to fuel mileage and increased fuel efficiency, this ratio changes again. All new cars run at 14.7:1 air-fuel ratio at part throttle because this is the lowest emission point. But depending upon the engine, it's possible to run an engine at leaner mixtures like 16:1 or more at part throttle to gain mileage. The difficulty with this is that drive ability and throttle response suffers at these ratios. Engine response is lazy and stumbles are commonplace. Each engine will be different, but there is fuel mileage to be gained by fine-tuning your carburetor. Don't be intimidated by these lean mixtures at part throttle. You won't burn the engine up since it is making very little horsepower at part throttle cruise--often less than 30 hp.
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Adam Schneider (12-07-2023)
06-28-2006, 09:00 PM
#7
"quote" BOOST-11.8-12.2 Ideal" quote" I was told that 12.0 and higher is too lean and the tune needs to be a tad richer at that paticular RPM and coresponding MAF frequency.I guess this is to error on the safe side. i was led to believe under WOT at full boost 11.5-11.9 is right at the safe sweet spot. please comment. We all want max power and safe conditions if possible. 
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Adam Schneider (12-07-2023)
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06-28-2006, 09:10 PM
#8
Originally Posted by TIM Z
"quote" BOOST-11.8-12.2 Ideal" quote" I was told that 12.0 and higher is too lean and the tune needs to be a tad richer at that paticular RPM and coresponding MAF frequency.I guess this is to error on the safe side. i was led to believe under WOT at full boost 11.5-11.9 is right at the safe sweet spot. please comment. We all want max power and safe conditions if possible.
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Adam Schneider (12-07-2023)
06-28-2006, 10:05 PM
#10
not me. I am shooting, errr I was, I am retuning now, but I will ultimately shoot for 11.7.
What I wonder is, in the E85 motors, a higher AFR is more tolerable. Is there a formula to work out a safe but leaner scenario for running meth injection.
I would go to guess, at WOT, using what we know with our injector formulas we can get pretty close to a reasonable speculation of how much pump gas is going into each cylinder. Then with what ever jetting at whatever pressure for your meth, figure out the same. Obviously again, using a speculative formula sense you are just dumping meth down the TB, but figure out what the meth amount is. Then with those two numbers, whats you pump gas to meth ratio. I would be interested in that. Blah blah blah right? I bet with parish's single turbo setup he is able to squeeze a little more of leaner afr out of it versus less meth (alcohol).
So, with that said, could we change the afr ranges if we introduced alcohol injection?
What I wonder is, in the E85 motors, a higher AFR is more tolerable. Is there a formula to work out a safe but leaner scenario for running meth injection.
I would go to guess, at WOT, using what we know with our injector formulas we can get pretty close to a reasonable speculation of how much pump gas is going into each cylinder. Then with what ever jetting at whatever pressure for your meth, figure out the same. Obviously again, using a speculative formula sense you are just dumping meth down the TB, but figure out what the meth amount is. Then with those two numbers, whats you pump gas to meth ratio. I would be interested in that. Blah blah blah right? I bet with parish's single turbo setup he is able to squeeze a little more of leaner afr out of it versus less meth (alcohol).
So, with that said, could we change the afr ranges if we introduced alcohol injection?
The following users liked this post:
Adam Schneider (12-07-2023)