I keep seeing threads about the MAF mod and understand the concept, but I can’t figure out exactly what’s suppose to be done, I have a 02 4.0 sohc and this is what my MAF looks like, pointers on what needs to be modified?

 

MAF = MASS air flow
Mass being the key word, MAF sensor is there to WEIGH the incoming air, MAF data is used by computer to calculate the MASS of the in coming air

14.7:1 gasoline air:fuel ratio is a WEIGHT Ratio
14.7 pounds of air to 1 pound of gasoline
14.7 grams of air to 1 gram of gasoline

This is why Fuel Injectors are rated in POUNDS of gasoline per hour, not gallons or liters, POUNDS, because its a weight ratio

Cold or warm, gasoline's weight doesn't change much
Cold or warm, air weight changes ALOT

It's how Hot Air balloons work, "hot air rises", why,?
Because its lighter than cooler air, so a balloon filled with Hot Air will float up above the cooler air around it

You can add more gasoline to colder heavier air because mix is a WEIGHT ratio, its why people use Cold Air Intakes(CAI), all 1986 and up Rangers come with that, just FYI
When you can add more gasoline you get more power released
If you just add more gasoline you get a flooded engine not more power, lol

If you think the size of the MAF passage is restricting air flow to the engine at WOT(wide open throttle) then a larger diameter MAF may be needed, but stock size is plenty for stock 4.0l SOHC
Diameter would only be an issue if you modified the engine so it could use more air at WOT

On any engine you can hook up a vacuum gauge you can see in the cab
Then find a stretch of road that you can run at WOT and higher speed, no police around, lol
At WOT you should see 1"-2" of vacuum until Valves Float and it drops to 0"
Over 2" could mean a restriction, on intake air OR Exhaust OUT

MAF sensor itself only samples say 15% of the incoming air, this % is programmed into the computer, computer then calculates total air weight from this
So changing the diameter of the opening and using same sensor would throw off that %, so throw off computer calculation

There is also an Air Temp Sensor, IAT or ACT, used in conjunction with the MAF data to calculate air weight so computer can added correct weight of gasoline

To get more power from any engine you need to get it to use more air, so more gasoline can be added
Thats what "larger Cams" are for, engine gulps a bit more air thru the valves
Or what turbo or super changers do, FORCE more air into the engine so more gasoline can be used at the 14.7:1` ratio
And of course larger displacement, 5 liter engine can gulp more air than a 4 liter engine, so can use more gasoline at 14.7:1 and get more power released

Car makers sell performance, so most stock systems are the best that stock engine will do
Back in the 70's and early 80's car makers had to detune systems to meet emissions requirements, those days are long gone now, better engine designs and Cat Converters mean engines can be tuned for best performance