Uberdata formula

[high c]

So to those who have used uber a lot (acclude, MRX, r33...) i was just wondering if there is some way to develope a mathmatical formula to figure what the fuel value should be in any given cell? I am 'mathmatically inclinded' and was just thinking there has to be a more efficant way of tuning my car then driving around logging it, changing the map accordingly, then test again. I mean shit, 93 is expensive

if i am being unclear, i am meaning taking the vac/boost level, figuring how it relates to the fuel value in the cell, for any given injector size, to the a/f ratio. I figure those are the four variables, vac/boost, injector size, rpm, and what a/f you want to be at.

Also because the curve isnt going to be linear (so i cant just take a slope of it and work from it) i could prob use it like a parabula and figure it that way...

if someone out there were to be able to tell me for example "the a/f ratio is 14.7 when i am at 3k rpm running 15 in/hg of vac with 450 cc injectors, the value in my uber cell is XXX"

The biggest values i am concerned with are 14.7 out of boost to get the good fuel efficancy of a DD, and 12.5 in boost, which is a good conservative ratio to run while under boost. I figure the values from changing from vac --> boost would just be mod-ing the out of boost values between what they are currently, and the boost values.

I know i can make a formula for them, im not saying it is going to be easy, but i figure if i were to do something like this then it would benifit both myself, and pretty much everyone else on this site that is running uber. And im not saying that you guys make bad base maps at all (everyone that i have ran is great) just taking them to the next level

mods, if this isnt wehre it is suppose to be then by all means move it

[Accord R33]

The main problem when trying to figure this out, is that Hondas use a MAP sensor, and they rely on pressure. What you really want is the mass of air going into the cylinders, which is impossible to figure out, since everywhere on earth, the air is of different densities, it even changes day to day. so even if you were able to figure out the density, and get a solid formula, you would need some way to meter and compensate for when it changes, which is basically out of the question.

On a related note, this is entirely possible with MAF sensors, and having written my own Nissan "uberdata" type software, i can tell you its very easy to calculate exact fuel values using the MAFS signal, since it measures the mass of the air, not the pressure.

at first glance one would think a MAP sensor is better for tuning, but having tuned both, iv learned that MAF sensors are just easier and more accurate. once you get past the fact that you need a recirculated BOV (unless you do a blow through MAF), there is really not many (there IS some), but not many advantages to a MAP sensor

[high c]

wow that was fast eric! Ok, so i understand what it is you are saying about the density of air that is going into the cylinders and how that is going to change the rich/lean ratio of the fuel. Another way of saying this (and correct me if i am wrong):

if i were to tune my car perfect for 14.7 out of boost at sea level, and then drive my car up a mountain it might run more lean/rich depending?

I geuss where i am having a hard time grasping what you are saying about the cylinder pressure, is that it does vary, but i cant see it varying so much, that if my car was running 12.5 at 10 psi, the next day due to humidity, etc, it might run a little leaner/richer....

i understand that i am not going to be able to keep the a/f at 14.7 throughout the whole rpm band out of boost, but from the variances with different densities of air it shouldnt make it vary more then .2ish (example) either plus or minus. Know what i mean?

also i geuss i do kinda have a ? about air density. All of the air going into my engine (other then teh amount that is being sucked in by the IACV) is comming from the turbo, going throuhg the intercooler, and into the tb and intake plenum. So how would it not remain pretty constant, other then temp and humidity of it?

thanks bud
justin

[MRX]

agreed, the map sensor allows for way too many variables. It can't be that bad trying to tune lol. Come on man i can do a motor from start to finish in just a couple hours now. I thought u had soy with you?

[Accord R33]

its hard to explain, but you have to understand you can have a very different number of air molecules at the same PSI at different places/times.

I guess it would be somewhat possible to formulate something. you would need to figure out how much mass the air in the cylinder has at say, an average density. then you would need to figure out how much fuel is flowing at a certain pulse width, figure out how dense the fuel is, and find a way to compair an average number of air molecules to the average number of fuel molecules. then figure out the correct amount of both to create your desired A/F ratio....

This is all assuming averages though, with a MAF, its much more exact

[maroonaccord2.2]

This is an interesting discussion. In regards to air density/humidity/temp going through an I/C being consistant..... Maybe I'm preaching to the choir, well shoot..... I know I am but temp varies with pressure, and the boost curve would look something like a parabala if it were graphed out.

Anyhow, very good info seeing as how I have minimal boost experience, but I understand the basics I guess.....

[MRX]

i can answer that too.

By too many variables i'm talking about humidity, air density, air temperature, engine temperature, and overall air quality. If you tune at sea level and have a perfect a/f of 14.7 in vac and then tune again at a higher altitude the a/f will most likely be higher. For example i usually tune at the subaru dealership and the techs say that STI's and WRX's that come from Atlanta, GA down to Jacksonville, FL run 1 full a/f ratio richer here than they did in Atlanta. This is mostly due to humidity and density of the air. Goes to even show that the MAF's aren't perfect either. The 12.5:1 a/f that your shooting for is too risky IMO because of what we just talked about. The chance of running leaner or richer in a given area is what i call the "a/f swing" and i try to compensate for that occassion. I shoot for an 11.7 because its not too rich, and certainly not too lean. Vacuum is a different story. It doesn't have nearly as much of an effect on longevity as WOT and is alot more forgiving with the ratios. Honestly a 13.5 to 15.7:1 isn't anything damaging even for extended periods of time. But of course the 14.7 is optimal and rules out the a/f ratio as a possible trouble spot.

[Accord R33]

Atlanta, GA down to Jacksonville, FL run 1 full a/f ratio richer here than they did in Atlanta. This is mostly due to humidity and density of the air. Goes to even show that the MAF's aren't perfect either.

MAFs have an inherent problem with humidity, they cant accurately distiguish between wet and dry air

[MRX]

I guess it would be somewhat possible to formulate something. you would need to figure out how much mass the air in the cylinder has at say, an average density. then you would need to figure out how much fuel is flowing at a certain pulse width, figure out how dense the fuel is, and find a way to compair an average number of air molecules to the average number of fuel molecules. then figure out the correct amount of both to create your desired A/F ratio....

But by the time he would be able to take into account all of the air variables, the cam specs (those would certainly matter), and VE of his engine someone else would have been done tuning his car already. And since every engine is different he couldn't use the same specs for even the same motor.

I'm trying to say that theres a point where theory and mathmatical calculations seize and real testing most be done.

[Accord R33]

But by the time he would be able to take into account all of the air variables, the cam specs (those would certainly matter), and VE of his engine someone else would have been done tuning his car already. And since every engine is different he couldn't use the same specs for even the same motor.

I'm trying to say that theres a point where theory and mathmatical calculations seize and real testing most be done.

I agree 100%. its just not worth it

[LoDollar92LX]

time to make a honda EMS system that uses a MAF

[high c]

thanks for getting back to my gents. I appreciate all your feedback and insight in this area, so thanks in advance. lots of useful information here that can be used by myself and others im sure.

All in all, i think it can be done, by all the time invested in making a formula i think evens out just going out and enjoying my boosted baby and just tuning it the trial and error method. Thanks a lot guys for your insight again.

[LoDollar92LX]

ill let you know when i get the MAF system working justin

[high c]

thanks mike lol, but i already ahve the 3 bar and a hella awesome map that acclude ripped me...how you converting it to MAF?