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Davidv

Modelled fuel + MAF questions

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Hey guys, 

I've recently gone back to using a MAF sensor, and I notice that with modelled fuel there is the option to have as a load axis "Air per Cylinder Measured" Which is awesome.

Since this figure comes directly from the MAF sensor I am assuming that a lot of the calcs for modelled fuel get bypassed. 
I also notice there's a seperate category for "MAF IAT" Rather than regular IAT, I assume this does the IAT calculation differently too.

However I have a few questions.

1. Options for load axis in the fuel calculation are either MAP, BAP, or Off. I've set this to Off. Would that be best option?

2. Which of the modelled fuel settings now get ignored, since you're measuring air directly?
I get the feeling that it air per cyl measured is used as part of the calc which then still generates "air per cyl estimated" which is what the fuel calc runs from?

I realise that MAF isnt the suggested option but it offers some benefits while I'm doing some experimenting with cam timing, so I'd just like to get it setup to "best practice". 
So any advice/info on how it calculates would be appreciated.

Thanks

David

It's pretty cool having grams/cyl as a load axis because the values are quite linear... This was the MAF basemap that I put together based on observation of my MAP based tune, and car ran awesomely on it! 

r2n5zz2l.s0n.jpg

It's now changed shape a little after the first iteration of tweaking it but it's still very linear.

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Hi David,

I dont have all answers and our documentation around MAF is a bit thin and barely anyone I know has used it, so I just done a few quick tests on the simulator to get some basic answers.

10 hours ago, Davidv said:

Since this figure comes directly from the MAF sensor I am assuming that a lot of the calcs for modelled fuel get bypassed. 
I also notice there's a seperate category for "MAF IAT" Rather than regular IAT, I assume this does the IAT calculation differently too.

With a MAF since you are measuring air mass directly so you dont need air temperature (to approximate the mass via density).  If you select " MAF IAT" then the fuel equation is not modified by IAT. - It really just becomes a parameter that is logged and has no effect.

 

10 hours ago, Davidv said:

1. Options for load axis in the fuel calculation are either MAP, BAP, or Off. I've set this to Off. Would that be best option?

I dont know this one confidently but I suspect "Off" is the most appropriate.  I cant see how BAP would affect the measured air mass so I dont think that is useful.

 

10 hours ago, Davidv said:

2. Which of the modelled fuel settings now get ignored, since you're measuring air directly?
I get the feeling that it air per cyl measured is used as part of the calc which then still generates "air per cyl estimated" which is what the fuel calc runs from?

It appears to me that if you use Modelled mode then "estimated" is used, if you use traditional mode and have a MAF assigned then "measured" is used.  That means to me that traditional mode is a more true MAF strategy but you then miss out on some of the fuel pressure/density comps.  In modelled mode if I do a test at a fixed mass air flow and change something like "engine capacity" I see "estimated air/cyl" change and pulsewidth change, so it seems the "air density model" is still trying to do its work in the background.

 

11 hours ago, Davidv said:

2. Which of the modelled fuel settings now get ignored, since you're measuring air directly?
I get the feeling that it air per cyl measured is used as part of the calc which then still generates "air per cyl estimated" which is what the fuel calc runs from?

If you wanted to use modelled mode then put the charge temp table to zero and make sure your IAT is set to "MAF IAT" so charge temp is taken out of the equation.  Provided the other air density related settings like "engine capacity" are left alone then it should provide a good MAF strategy.   

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