The heck with it. Snow is about to fly so get those tuning logs in soon.

 

No, I understand. I've tuned enough of these to know that the curve changes with each intake.

Some MAF Scalings actually lower in the low voltages and rise in the upper voltages. Others raise linearly in the lower voltages, but increase a lot in the upper range.

What you are doing is a good start, but some long term logging with some proper trim based maf scaling is in order. I usually tweak the upper voltage ranges some based off WOT pulls.

 

yeah i have trouble with this concept as well.

a 3.5" tube is almost 2x the cross sectional area of a 2.5" tube.

So the theory is the table should be multiplied by 2... But that doesn't work for some reason, you get values WAY to large...

The best thing todo is get a number of sample points (idle, 2000 cruise, 3500 cruise), get the STFT/LTFT trim change and then use that as the multiplier for the MAF..

Then interpolate the voltages in between by the same rough amount...

 

It's because we use a hotwire maf. Windchill is a squareroot type equation in relation to velocity. So doubling the air speed does not double the windchill. The voltage does not decrease linearly.

See table:

 

but with a larger intake the airspeed is actually less..

so you are saying that

2.5 -> 3.5 is a 2x increase in area.

but we need to sq rt that to get the new cooling affect

ie going from 2.5 -> 3.5 is a gain of 40% (140%)

 

Yes, but it is velocity based. I don't know what a good equation would be. We change MAF size and the MAF outputs different volts than it used to. Even looking at the stock MAF scaling, you can see that volts to airflow is not a linear graph.

It is much easier to empirically determine the air flow from current MAF Voltages than to try to come up with a flat equation. There are spread sheets out there that really help with this. I use a custom one that makes sure that STFT are != 0 for the calculations, because that usually means that we are not in closed loop. That will work for the 2.66 volts and less area. From there you have to guess at the high end. Here I like to run the car at WOT and see what the AFR is. I then scale it to get the AFR back to what it was with the stock MAF. I basically end up doing the same type calculations the fuel trims do at low voltages. Finally I smooth the line out.

 

Now if only we had an exact method to how the original values were created.. it would be very simple to use this same method to create a new table.. ahh, dreams..

 

thats basically exactly right B, we dont really know what the values mean.

well we do - I looked it up a couple of days ago...

I will post up how these numbers get converted into load in a little bit.

Then maybe someone can reverse engineer them to go back to something meaningful..

 

I think I can make a spread sheet that will calculate new MAF tables based on airflow changes. Now this won't account for eddy currents and flow characteristics of the new intake, but it can be used as a much better rough estimate when slapping on a new intake.

Also, I thought the stock MAF was closer to 2.83 when measured at MAF's location. Maybe I'm thinking of something else. I'll measure it tonight.

 

Are you measuring the radius of the pipe? Or the approx. sensors location within the tube? I'm kind of interested to know if the sensor is considering the air flow "above" it.. if that makes sense?

 

I was simply referring to the diameter of the pipe where the MAF sits. The stock MAF housing is tapered in several spots.

 

The MAF calibration table gives mass air flow rate as a function of MAF voltage. If you want to rescale the *output* side of this table for a larger MAF tube, then you want to know the increase in mass air flow rate at any given MAF voltage. I do not need wind chill formulas to estimate this. All I need to know is that at a given MAF voltage (and air temperature), the airspeed over the wire is going to a particular value, say "S". The mass air flow going past the wire (at a particular temperature) is going to be S*A where A is the cross sectional area of the MAF tube. Therefore, the increase in mass air flow rate (the output side of the calibration) is going to be proportional to the square of the MAF tube diameter. This is all in theory of course - The maf tube is not a perfectly straight tube and there is a hanger in the tube to hold the wire. These non-idealized conditions will cause the final value to be different than theory. However, as a first order recalibration, the MAF scaling table can be rescaled for a larger MAF tube using the following multiplication factor:

m = [(aftermarket maf tube inside diameter)/(stock maf tube inside diameter)]^2

where the diameter is measured at the location of the MAF wire.

 

I had 3dman1 measure the ID of the stock maf tube and the Primo. Stock is 2.72" ID at the MAF wire, and Primo is 3.32". Using my formula:

m=(3.32/2.72)^2=1.49

In my dialing in of the Primo, I started with about 1.8 because I didn't have the MAF tube measurements, and I assumed the stock tube was more like 2.6" and the Primo was more like 3.5". I ended up with 1.5 to get the cruise trim and WOT AFRs spot on with where they were with the stock MAF tube, so there ya go.

I will need to tweak the calibration slightly in the idle range, but not surprising.

 

Where are you guys getting your diameter squared stuff from?

The area of a circle is pi * radius ^2 or pi * ( diameter / 2 ) ^2


And I don't understand why you would take the square root of the ratio of diameters.

 

Diameter or radius is fine when taking the ratio of the MAF tube cross sectional areas. Radius is 1/2 the diameter, so when taking the ratio of tube size using the diameter, the factor of 1/2 cancels out from top and bottom.