Some Stage 3 MAF math - (say that three times fast (discussion))
#1
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(Obviously there are generalizations made in the below math and they should not be considered absolutes)
RS4 K04 turbo characteristics:
K04s at 1.6 bar (23.52psi(70% efficientcy)) flow approximately 0.15 m3/s (or approximately 318 cfm)
There are two turbos in the S4 so the total potential CFM should be 0.30 m3/s (or approximately 636 cfm)
MAF characteristics:
Stock S4 MAF 73mm
Common conversion 88mm
MAF reading offset 1.45 correction factor.
Topic for discussion:
If 1 g/s = 1.77 cfm (approximate average given temp modulation) then an 88mm MAF reading 250 g/s = 362.5 g/s (when correction factor is applied) would approximately equal 640 cfm.
(I realize that there are temperature range air density factors in the MAF conversion but, I chose to simplify the discussion by leaving that out since a 40-100 deg range assumes similar basic air density of modest significance)
Question for discussion:
How can a 1.6 bar, 636 cfm potential max boost system provide a MAF reading of greater than the total potential cfm?
Is my math wrong here?
No particular car is implicated in this example as this is a math topic for discussion.
RS4 K04 turbo characteristics:
K04s at 1.6 bar (23.52psi(70% efficientcy)) flow approximately 0.15 m3/s (or approximately 318 cfm)
There are two turbos in the S4 so the total potential CFM should be 0.30 m3/s (or approximately 636 cfm)
MAF characteristics:
Stock S4 MAF 73mm
Common conversion 88mm
MAF reading offset 1.45 correction factor.
Topic for discussion:
If 1 g/s = 1.77 cfm (approximate average given temp modulation) then an 88mm MAF reading 250 g/s = 362.5 g/s (when correction factor is applied) would approximately equal 640 cfm.
(I realize that there are temperature range air density factors in the MAF conversion but, I chose to simplify the discussion by leaving that out since a 40-100 deg range assumes similar basic air density of modest significance)
Question for discussion:
How can a 1.6 bar, 636 cfm potential max boost system provide a MAF reading of greater than the total potential cfm?
Is my math wrong here?
No particular car is implicated in this example as this is a math topic for discussion.
#4
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..."how can it be higher" rather than the "how much".
Because the topic could digress. I think my math may not correctly account for g/s (air flow) vs cfm (volumetric measurment) in the presented example.
Side note: The case of the vehicle in question is considerably higher.
Because the topic could digress. I think my math may not correctly account for g/s (air flow) vs cfm (volumetric measurment) in the presented example.
Side note: The case of the vehicle in question is considerably higher.
#7
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shouldnt it be:
73mm vs 88mm maf should be 1.2055
73mm X 1.2055 = 88 so if 88mm maf reading is 250g/s wouldnt it mean 301.375? then the CFM would be much lower!
73mm vs 88mm maf should be 1.2055
73mm X 1.2055 = 88 so if 88mm maf reading is 250g/s wouldnt it mean 301.375? then the CFM would be much lower!
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#9
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You could also have a boost leak on the pressurized side... metering more air then is actually being used, so you may be flowing 1.7bar worth of air to get your 1.6.