This is information I thought I would post, just because it might be useful to some of you other guys thinking about going the big turbo route.

Just about every week I do some logs with the vag-com to make sure timing, knock, etc is all safe, I recently upped the boost to 17psi, and did a log last week. I decided to log maf values just because I was curious and came up with this:

Engine Air
Speed Mass Flow
/min g/s
1960 3.68
1960 9.17
2040 15
2200 17.43
2360 22.01
2600 36.18
2920 51.18
3280 78.19
3840 131.73
5000 187.98
5840 187.43
5920 187.22
6480 187.43
7120 187.64
7680 187.64
6920 42.78
5960 13.68
5240 164.37
5840 187.15
5800 187.22
6080 187.71
6360 187.15
6600 187.01
6880 187.36
7120 187.43
7400 187.57


Now, I am running a 3" vr6 maf (2.75" ID), and 440cc injectors. As you can see my current maf is being maxed out around 5000rpm at 17 psi, at this point I see plumbs of smoke out the exhaust followed by fireballs when switching gears. I'm assuming the ecu sees that the maf is maxed out and is dumping fuel to be safe.

To resolve this problem I happen to have an s4 maf laying around which has a 3" id. The reason why a bigger maf will solve this problem is because much more air can flow through the larger surface area, at a lower reading of the maf sensor. However I can't just throw in the bigger maf, otherwise I will run out of fuel and cause a lean/dangerous situation. The ecu opens the injectors a certain amt depending on the maf reading as well as other things.

To calculate fuel I had to do some math. I am currently running a 2.75" id maf, 440cc injectors at 43.5psi, and I need to calculate how much fuel to use with a 3" maf so here's what was done:
First calculate the maf scale:
[(.5)(3.14)(new maf radius)^2]/[(.5)(3.14)(old maf radius)^2]=[(new maf radius)^2]/[(old maf radius)^2]
Turn diamter into radius to use in above equation
3/2=1.5
2.75/2=1.375
(1.5)^2/(1.375)^2 = 1.19

Next calculate the amt of fuel needed:
440cc(1.19)=524cc

Finally, calculate the amt of fuel pressure needed to increase the flow of the injectors from 440cc to 524cc, if it's reasonable I will go this route instead of new injectors:
% increase in injector flow=square root of [(new pressure)/(recommended pressure)]
1.19= square root of (new pressure)/43.5
new pressure=61.6psi, which is equal to 4.24bar.

Therefore I can now run my 440cc injectors as 524cc injectors and use an s4 maf, and still be in the same scale. This should keep things safe, and the ecu happy


I will post how this works out once my fuel trims adapt. I will also post some pics of maf sizes and stuff if i can find my camera. Thanks to speedyg on vwvortex for the help with the math!

 

umm..i think i needa tutor...

 

Looks OK, but you don't have to multiply the radius by 0.5.

The formula should be 3.14(0.5 x dia)^2.

See even at my age, some of the neurons still work.

 

Ah true, I actually multiplied the diameter by .5 to get the radius, but I shouldnt have written it like that, I'll edit it now

 

What the hells ur problom thomas, that math is easy, get it right.
















j/k

 

LOL, if I screwed up enough, my motor could go boom so I'm glad ppl are pointing these things out!

 

See I knew there was a reason to stay awake during math class!

 

*stares blankly in a fog of ignorance*

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