making sense of flow numbers..
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making sense of flow numbers..
say you have your exhaust manifold (1.8t) flow tested and it flows 197cfm (volumetric flow rate).
at room temperature this converts to 108g/s (mass flow rate)
compared to what a WOT chipped maf reads (at room temp) this, 108g/s is low. why the disparity? is too much of a simplification?
(btw i understand thermodynamics, but im wondering if the simplification is or isnt valid)
at room temperature this converts to 108g/s (mass flow rate)
compared to what a WOT chipped maf reads (at room temp) this, 108g/s is low. why the disparity? is too much of a simplification?
(btw i understand thermodynamics, but im wondering if the simplification is or isnt valid)
AudiWorld Super User
Joined: Mar 2000
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Where did you account for back pressure?? (EDIT)
That's what it would flow with no restriction to air flow. You can flow more than that it just has to be "forced" out and will create back pressure and heat.
Just for kicks I went ahead and ran some calcs. For simplicity I'll assume that it flowed 197 cfm under "standard" conditions (19F and 1013 mbar pressure). Under those instances you would flow ~110 g/s.
However, your exhaust gas is hot and a turbo car has high pressure in the exhaust manifold. Usually the exhaust manifold pressure is twice the intake pressure (or higher on stock cars). I'm going to assume your exhaust temperature is 1500 F and your EMP is 4000 mbar absoute (about 15 psi intake).
Pressure Adjustment:
110 g/s * 1013/4000 = 28 g/s
Temperature Adjustment:
28 * (273+1500)/(273+19) = 170 g/s
I don't really know 1.8T's so how did I do?? I had to take liberties with my assumptions so hopefully they are in the ballpark for a chipped 1.8T.
To answer your question, you were WAY to simplified.
Just for kicks I went ahead and ran some calcs. For simplicity I'll assume that it flowed 197 cfm under "standard" conditions (19F and 1013 mbar pressure). Under those instances you would flow ~110 g/s.
However, your exhaust gas is hot and a turbo car has high pressure in the exhaust manifold. Usually the exhaust manifold pressure is twice the intake pressure (or higher on stock cars). I'm going to assume your exhaust temperature is 1500 F and your EMP is 4000 mbar absoute (about 15 psi intake).
Pressure Adjustment:
110 g/s * 1013/4000 = 28 g/s
Temperature Adjustment:
28 * (273+1500)/(273+19) = 170 g/s
I don't really know 1.8T's so how did I do?? I had to take liberties with my assumptions so hopefully they are in the ballpark for a chipped 1.8T.
To answer your question, you were WAY to simplified.
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