are you looking to change something on your truck?
Air:fuel ratio
- Thread starter laserjock
- Start date
are you looking to change something on your truck?
I’ll apologize up front for the long winded rambling post you are about to receive. Bear with me. I’m still learning here. 
I worked up a spread sheet that starts with fuel volume based on rpm and data I found in a really old forum post on the moose pump. It covered the defueling with rpm so I worked that in. From there calculated horsepower etc based on fueling (which comes out fairly close to what I’d expect). Calculating air required to burn that fuel which is where turbo stuff comes in.
I kinda disagree with you on being too lean. Horsepower is really only a function of fuel volume so long as you are over stoichiometric on a diesel. It seems like most people set AFR at just above Smokey pig because it requires the least effort for reasonable results. That’s all well and good. All the reading I’ve done so far says there’s no such thing as too lean on a diesel which is completely opposite of gasoline or alcohol. Since the air is basically unmetered, idle AFR may be 200:1. The leaner the burn on a diesel the cooler it is running EGT wise mainly because you are diluting the heat. The fuel will produce roughly the same energy (heat) regardless as long as you are above stoichiometric. The more air you can cram in there the better (cooler).
Factory type tunes tend to stay very conservative (in the 20’s). This is for emissions and warranty issues I’m sure. Turning the pumps up pushes you into the 16-18 kind of range( assuming it’s not grossly over fueled) because while there may be some small change in turbo performance at steady state you really are pushing about the same amount of air because the RPM is not really changing and there is a lot more air than fuel in the combined exhaust (conservation of mass says what goes in must come out, roughly).
So really, as long as you have enough air, it seems to come down to driveabilty. I suppose there could be such a thing as too much air in the sense that you have to compress that air and that is cylinder pressure which can cause mechanical issues, but other than that I think it comes down to practicality.
I worked up a spread sheet that starts with fuel volume based on rpm and data I found in a really old forum post on the moose pump. It covered the defueling with rpm so I worked that in. From there calculated horsepower etc based on fueling (which comes out fairly close to what I’d expect). Calculating air required to burn that fuel which is where turbo stuff comes in.
I kinda disagree with you on being too lean. Horsepower is really only a function of fuel volume so long as you are over stoichiometric on a diesel. It seems like most people set AFR at just above Smokey pig because it requires the least effort for reasonable results. That’s all well and good. All the reading I’ve done so far says there’s no such thing as too lean on a diesel which is completely opposite of gasoline or alcohol. Since the air is basically unmetered, idle AFR may be 200:1. The leaner the burn on a diesel the cooler it is running EGT wise mainly because you are diluting the heat. The fuel will produce roughly the same energy (heat) regardless as long as you are above stoichiometric. The more air you can cram in there the better (cooler).
Factory type tunes tend to stay very conservative (in the 20’s). This is for emissions and warranty issues I’m sure. Turning the pumps up pushes you into the 16-18 kind of range( assuming it’s not grossly over fueled) because while there may be some small change in turbo performance at steady state you really are pushing about the same amount of air because the RPM is not really changing and there is a lot more air than fuel in the combined exhaust (conservation of mass says what goes in must come out, roughly).
So really, as long as you have enough air, it seems to come down to driveabilty. I suppose there could be such a thing as too much air in the sense that you have to compress that air and that is cylinder pressure which can cause mechanical issues, but other than that I think it comes down to practicality.
I have a couple areas of concern with my setup, but honestly I’m trying to develop a tool here that can be applied to various applications using my truck as the example.
I’m a little concerned my turbine housing is a little small although looking at R&D’s stuff it’s in the ballpark of his stage 1 turbo which should digest my pump fine. The other thing is my IC. I’m a little concerned that it’s too small and I’m taking a hit on it. That’s the reason for calculating air flows and such because I can find the pressure drop curve for it to check it.
I’ll apologize up front for the long winded rambling post you are about to receive. Bear with me. I’m still learning here.
I worked up a spread sheet that starts with fuel volume based on rpm and data I found in a really old forum post on the moose pump. It covered the defueling with rpm so I worked that in. From there calculated horsepower etc based on fueling (which comes out fairly close to what I’d expect). Calculating air required to burn that fuel which is where turbo stuff comes in.
I kinda disagree with you on being too lean. Horsepower is really only a function of fuel volume so long as you are over stoichiometric on a diesel. It seems like most people set AFR at just above Smokey pig because it requires the least effort for reasonable results. That’s all well and good. All the reading I’ve done so far says there’s no such thing as too lean on a diesel which is completely opposite of gasoline or alcohol. Since the air is basically unmetered, idle AFR may be 200:1. The leaner the burn on a diesel the cooler it is running EGT wise mainly because you are diluting the heat. The fuel will produce roughly the same energy (heat) regardless as long as you are above stoichiometric. The more air you can cram in there the better (cooler).
Factory type tunes tend to stay very conservative (in the 20’s). This is for emissions and warranty issues I’m sure. Turning the pumps up pushes you into the 16-18 kind of range( assuming it’s not grossly over fueled) because while there may be some small change in turbo performance at steady state you really are pushing about the same amount of air because the RPM is not really changing and there is a lot more air than fuel in the combined exhaust (conservation of mass says what goes in must come out, roughly).
So really, as long as you have enough air, it seems to come down to driveabilty. I suppose there could be such a thing as too much air in the sense that you have to compress that air and that is cylinder pressure which can cause mechanical issues, but other than that I think it comes down to practicality.
All fine and good, but it takes power to pump air.
That is also true. I think it comes down to what your goals are. If you are running empty or just need short bursts where sustained EGTs are not a problem, fatten it up.
I intend this to be a discussion. I suspect I know what the answer is but I would like others to weigh in.
I intend this to be a discussion. I suspect I know what the answer is but I would like others to weigh in.
That’s really cool you are doing that table, if you need any data from me just let me know. As far as the target air:fuel ratio the reason I said go with 17 is because beyond that I found I had diminishing returns as with egts vs power. It seemed (at least in my situation- your truck is setup very different) that anything leaner than 17:1 I had less and less of a decrease in egts but still continued to loose power at the same rate as from before.
For example:
Changing from 14:1 to 16:1 net me about 350* drop in egt and a drop in power, but the drop from 17:1 to 19-1 dropped 75-50* but still dropped the same amount of power.
Really enjoying this discussion and looking forward to seeing what you can come up with and what others may have to add.
I’ll try put a video together with a summary of my findings and with some driving under various conditions with some explanations, I think they would be best since not everyone can read a data log and because I sold all my software licenses to a friend, he’s local so I could get data logs if I need to but just not as convenient
For example:
Changing from 14:1 to 16:1 net me about 350* drop in egt and a drop in power, but the drop from 17:1 to 19-1 dropped 75-50* but still dropped the same amount of power.
Really enjoying this discussion and looking forward to seeing what you can come up with and what others may have to add.
I’ll try put a video together with a summary of my findings and with some driving under various conditions with some explanations, I think they would be best since not everyone can read a data log and because I sold all my software licenses to a friend, he’s local so I could get data logs if I need to but just not as convenient
You are absolutely correct you cannot have to lean of a situation with a diesel, it’s really the biggest benefit of its design because it doesn’t need to maintain a certain afr mixture to stay running so in my truck I can cruise down the highway at 40:1 and use very little fuel while a gas engine would have to stay below 20:1 regardless of displacement or load, while a diesel can idle at more than 200:1 like said before, diesels are awesome.
Before the moose pump I would adjust the fuel screw to control the max fuel injected, now with the moose pump I control it with my right foot, haven’t noticed a difference in afr between those two changes. The truck I am referring to is NA so the only thing that changes is fuel for me, so I can compare more and less fuel and how it affects the engine directly.
Your setup is more complicated so experimentation is your friend. If you want to use it, I’ll pull the afr gauge and o2 sensor off my truck and you can use it on big red
That makes sense. So it would make sense that if you are turning down the fuel, you are turning down the power.
I appreciate the offer on the o2 sensor. Could you post up the PN’s?
I may have my buddy weld some bungs in my charge pipes to look at temps and pressures. We shall see.
I appreciate the offer on the o2 sensor. Could you post up the PN’s?
I may have my buddy weld some bungs in my charge pipes to look at temps and pressures. We shall see.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/160999834586
That is what I use, I’ve had it on many vehicles before this one but if you buy the kit it comes with more than enough to install it
That is what I use, I’ve had it on many vehicles before this one but if you buy the kit it comes with more than enough to install it
the only thing we need to setup now is a dyno day for IDI week.
now mike i think the only difference in our engine setups is you have a bigger pump and a smaller exhaust housing and i am the opposite. i would be curious on the numbers i would get if i did the same tests because i haven't been able to run mine to the too hot point.
now mike i think the only difference in our engine setups is you have a bigger pump and a smaller exhaust housing and i am the opposite. i would be curious on the numbers i would get if i did the same tests because i haven't been able to run mine to the too hot point.
I’ve got access to a dyno down here... my current engine is going to be getting replaced with something I’ve been building for about a year, that setup will be spending a good amount of time on the dyno.the only thing we need to setup now is a dyno day for IDI week.
now mike i think the only difference in our engine setups is you have a bigger pump and a smaller exhaust housing and i am the opposite. i would be curious on the numbers i would get if i did the same tests because i haven't been able to run mine to the too hot point.
Recorded the video this morning, going to edit it so it is semi-watchable. Talking/filming/shifting 5spd is a bit much to do at the same time
I’ll try to make it to the east and west coast meets if they work with my work schedule, be happy to dial in anyone’s truck if y’all want
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my truck made it into the slideshow 
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