Maths

[RealMcCoy]

It was solved by moles. There is a ratio of 11.5 air molecules to 1 fuel molecule.

I was just skimming, I see where I misread... It was the statement of how many liters 1 mole of fuel occupied that sent me on the wrong train of thought.

You DID solve for only 6(ish) lbs. above atmospheric though.... If you wanted 20 psi above atmospheric you need to convert 34.7 lbs to 239.48 kilopascals

[Memphetic]

I was just skimming, I see where I misread... It was the statement of how many liters 1 mole of fuel occupied that sent me on the wrong train of thought.

You DID solve for only 6(ish) lbs. above atmospheric though.... If you wanted 20 psi above atmospheric you need to convert 34.7 lbs to 239.48 kilopascals

Are you sure...? Can you show me an article that makes this evident? I think that was the most confusing part about this. I was almost certain that I would have to add 14.7psi, though, as like I said, an engine is a vacuum.

[RealMcCoy]

As a force there is no such thing as vacuum.... It's simply another measurement of pressure. It's an easy way to measure pressure levels below atmospheric. If you are going to calculate the air mass entering the engine, you have to measure it all, not just what you added above atmospheric.

If you are under boost conditions, at no time will you see a vacuum in the motor anyway.

[Memphetic]

I suppose I may be an idiot because obviously if you put a zero into the equation (representing 0 kpa), it would fail to work... likewise, entering something, say, -10 PSIg, would yield negative results. Thinking isn't necessarily straight that late at night :P

After redoing, resulted in 1166.368 cc/min.

This would be a duty cycle on stock 360cc injectors of 54%, ~510 cfm of airflow, with a MAF frequency of about 2080Hz. This volume sounds *way* more appropriate to me, but the duty cycle seems off :-P

[anyonebutme]

I suppose I may be an idiot because obviously if you put a zero into the equation (representing 0 kpa), it would fail to work... likewise, entering something, say, -10 PSIg, would yield negative results. Thinking isn't necessarily straight that late at night :P

After redoing, resulted in 1166.368 cc/min.

This would be a duty cycle on stock 360cc injectors of 54%, ~510 cfm of airflow, with a MAF frequency of about 2080Hz. This volume sounds *way* more appropriate to me, but the duty cycle seems off :-P

You're going to need better equation, quite simply. Something that takes into effect BSFC when you are dealing with fuel flows even at a basic scale like this. Or you can assume it's 70%ish at peak torque and maybe 50-60% at peak HP and just adjust your fueling numbers afterwards.

[RealMcCoy]

Edit: nevermind.... bad math post

[sergechronos]

Just further proof that math has never solved anything for anybody :P

[akotten]

I've created an excel doc that calculates this for you if you'd like me to share it...

Well...mine does it a little differently. It calculates the amount of fuel (ms duty cycle) to inject to obtain a specified AFR given certain paramters. (injector size, cylinders, MAF, stoich fuel, etc) Not sure if this will be helpful to you.
If you can figure out our MAF, it should be cake.

Fuel Injection Calculator.xlsx (13 KB)
https://mega.co.nz/#!nZ4WwKSD!XFy7Z2...cyx4XoWm6UlNa0


Google Docs version here
https://docs.google.com/spreadsheet/...Xc&usp=sharing

[futurevr4man]

The main factor that I'm not understanding... is CFM from the turbo. Obviously a larger turbo pushes more CFM at the same PSI. Or does it? Where is it reflected in the ideal gas law? The only place I can figure would be in the temperature of the intake charge.

The reason for this thread... I will be developing an air/fuel controller that will include standalone logging onto an SD card (or android/pc app via bluetooth or cable, both supported), as well as a 3D fuel map based on engine speed and load, that runs at a 100mHz clock speed. Essentially this would convert any Mitsubishi car into one with speed density, amazing logging capabilities, and more precise tuning than can be achieved with most of what is available from big name companies. In addition, my target price is around $300 ;-)

i dont have time to read this whole thread, but its not as cut and dry as saying a bigger turbo will make more CFM at the same psi. disregarding turbine design, friction forces on the air, and the temperature increase/decrease that a bigger turbo would create... the psi that you hit is a measurement of restriction from the engine. if you have an engine that can breathe 500cfm and a turbo that pushes 300cfm compared to one that pushes 400cfm, then it will be hard to build much pressure BUT you will still have an increase in airflow. obviously this is a very exaggerated example, however, the majority of people i talk to about this dont seem to get it.

[Memphetic]

i dont have time to read this whole thread, but its not as cut and dry as saying a bigger turbo will make more CFM at the same psi. disregarding turbine design, friction forces on the air, and the temperature increase/decrease that a bigger turbo would create... the psi that you hit is a measurement of restriction from the engine. if you have an engine that can breathe 500cfm and a turbo that pushes 300cfm compared to one that pushes 400cfm, then it will be hard to build much pressure BUT you will still have an increase in airflow. obviously this is a very exaggerated example, however, the majority of people i talk to about this dont seem to get it.

And as a result of not reading, you miss the intention and question :-P