Scaling MAF for Intake

footlong70 · Apr 17, 2015

tbsimmons said:
I will have to disagree with that statement and not a agree to disagree. It has to do with how much air the engine is digesting. Put the stock intake on. If your theory is correct and mine is wrong the truck should run totally different, as in worse at low throttle angles. In my opinion you are just getting the MAF scaled to the air flow at low throttle angles, nothing with the volume of the intake. You would have a bunch of extra fuel down low because you have told the PCM that now when the MAF is reading this frequency expect this much air. Another way is to put a tune in your truck that has more fueling down low and put the MAF tables back to stock. The truck will have more power down low because of the low throttle angle fueling. I didn’t notice one bit of difference in power in my truck from the a drop in AFE to a No Limit Intake with the stock chargers.
MAF has more than just measuring air, temp also.
If say at 5% throttle the tables are used to supply X amount of fuel.
Now at 5% you are getting more air into the engine and the same X amount of fuel is supplied the vehicle will run different, be it gas or diesel.
Now with bigger turbos you tell the MAF that at this 5% of throttle angle you need Y amount of fuel the truck will run different than with X amount of fuel. Which is what the MAF tables do, add or subtract fuel based on air.

The only way to get more air into the engine is build a motor or bigger chargers. An intake is not going to change the intake air requirement of the engine. It might not supply the required amount but the intake is not what determines air flow.

The only way the MAF would need to be scaled for the same amount of airflow would be if (2) intakes Y together and are of equal size and the MAF is only on one of the legs of the Y. If not the engine is taking in the same amount of air then the MAF would not have to be scaled. Look at the size of the inlet of the Turbo, that is staying the same. What you are saying above is partially correct but has to do off grams per second and the frequency the MAF sends to the PCM for fuel. The only way that can change is with a bigger turbo sucking more air at a given throttle angle. The above yes a 4” will have more velocity than a 5” but the air requirement of the engine is still the same.

I am taking that you need to scale the MAF for an intake, I thought that was the point of the dicussion.

Many reasons could have been used for the 2.75-4”. One is the injectors were way to big and the injector constant was not adjusted. With the vehicle idling it was thinking it was seeing a load and dumping fuel. The other was that the MAF tables were so far out for the given load that it was either pulling a bunch of fuel or dumping it. MAF is usedis for fueling (Along with MAP, injector size, etc.) before the vehicle sees a load bigger than whats programmed to switch into the fueling for power. Closed Loop to Power Enrichment or Open Loop for a gas engine for example.

Sorry mang but the more I read your replies the more I'm disagreeing. You've got this so much more complicated than it is. For starters yes, if I put the stock intake on with the modified map the truck would run rich. Simple.
Secondly volume of the intake has nothing to do with the maf after the sensor. I know that. Turbos do not have anything to do with the maf. The maf on the 6.4 is utilizing air velocity for a for an electrical signal for the pcm. That's it. It doesn't do any thinking or calculating. The whole point of this thread is making sure the maf sees the CORRECT amount of air coming in so the pcm can use the CORRECT amount of fuel. We are changing the velocity the air passes the maf by making the area larger AT the maf due to different sized intakes AT the maf. Larger intake AT the maf will flow slower than a smaller I.d. With the same amount of air being forced through. Therefore the sensor is not seeing the correct volume per second passing the sensor Entering the motor. Hence the map adjustment. The maf is utilized much more than just down low. I don't know how else I can put it but I know I'm correct and I'm very confident in the practice.

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tbsimmons · Apr 17, 2015

Right on man. Keep trucking then. I have just tuned many boosted and Nitrous vehicles with and without a MAF. You have to get the MAF dialed to the injector size and the amount of air. Ex air after a charger be it turbo or super, the HZ is going to be way higher because of airflow than it would be before. Therefore you have to rescale the tables on the amount of boost per the load.
It might sound difficult because I understand the reason for the MAF for low throttle fueling Like I said above "0" out your tables and see what happens to the fueling.

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footlong70 · Apr 17, 2015

Also just to clarify the theory is based on constant air temp and barometric pressure variables (air density). Which would affect maf interpretation.

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Gearhead · Apr 17, 2015

Yes this is needed sometimes. Also the position of the sensor relative to any turns in the pipe can make a very big difference...

footlong70 · Apr 17, 2015

Gearhead said:
Yes this is needed sometimes. Also the position of the sensor relative to any turns in the pipe can make a very big difference...

Yes absolutely. That's why I had mentioned the fact both stock and no limit are straight piping before and after the sensor for several inches so we are fairly safe to assume bends aren't a significant factor. But yes a important point.

makaveli200369 · Aug 4, 2015

Footlong70 I agree with what you're saying. The rescaling of the table allows correct calibration of the sensor output vs air flow. If the stock diameter of the intake pipe is 4" and you put that sensor in a intake pipe that is (we'll go on the extreme) 36" in diameter. If you flow 100CFM of air through the 4" pipe you could say there would be a measurable amount of velocity. 100CFM through that same huge 36" pipe you would barely feel a breeze. The sensor would barely register any frequency and think there is no air flowing into the engine. Now if you rescale the MAF accordingly it would know that the small amount of frequency is now equivalent to correct amount X grams/s. These engines can be run or tuned without a MAF because it has a MAP sensor on the intake and air flow can be calculated from that just like speed density. Whenever I see a vehicle that uses a MAF and Speed density system at the same time usually the MAF is used for low speed/part throttle readings because it reacts faster and is more granular then switches to MAP during boosted situations. When tuning the Nissan GTR it uses both systems you can eliminate the MAF and run off speed density or you can rescale the MAF if you change to larger diameter higher flowing MAF tubes. For a race car all out situation sure the speed density and elimination of the MAF offers slightly more airflow. But on the street application where you spend lots of time low speed/economy the MAF offers an edge.

Whether the 6.4 does this or how much of an importance the engineers placed on that scaling I couldn't say. But I can say for a piece of mind I'd rather have my MAF correctly scaled if its placed in a larger diameter MAF tube.