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Old 01-22-2009, 02:10 AM   #1
3rdangle
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Member#: 142335
Join Date: Mar 2007
Default Curve Fit Test Data on Breathing Capacity of Stock '07 STI

From acquired data on 2007 STI for boost > 1 psig (882 of 38313 data points using Ecutek DeltaDash):

RPM: 1800 to 6800 rpm, PSIG: 1.0 to 18.0 psig

PPM = ( a + b*RPM + c/PSIG + d*(RPM^2) + e/(PSIG^2) + f*RPM/PSIG )*PSIG

a = 2.3624697745957365E-02
b = 1.7202030655447530E-04
c = -2.8041056560228700E-01
d = 1.0516747850613378E-08
e = 3.0268800278786051E-01
f = 2.6850163893927669E-03

Example: Find approx. required CFM to achieve 14 psig boost at 4500 engine rpm.

For 14 psig @ 4500 engine rpm: PPM = 26.0 lb/min, CFM = 340 cfm ((26.0 lb/min)/(0.0765 lb/ft^3), @ 59 degF & 14.7 psia)

Note: Use at your own risk.
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Old 01-22-2009, 02:48 AM   #2
NSFW
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05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

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If I'm reading this correctly, you've basically come up with an equation that provides VE (though measured in lb/min) at a given RPM and manifold pressure?

Is there a reason to prefer this approach over a VE table, with manifold pressure on one
axis and RPM on the other? With a VE table it's much easier to visualize what's going on.

Is there something you're trying to achieve next, once you feel confident about this?
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Old 01-23-2009, 02:23 AM   #3
3rdangle
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Default Re: Curve Fit Test Data on Breathing Capacity of Stock '07 STI

Another way to look at it, is the pressure restriction the engine poses to increasing the air intake mass flow rate. The objective is to make it easier to calculate an operating point for a new compressor, given a compressor map. The supplied equation works nicely in an EXCEL spreadsheet. Besides, where does one find a VE table for an '07 STI available online?
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Old 01-23-2009, 02:36 AM   #4
NSFW
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Seems to me it should be possible to come up with a VE table with lots of logs and some Excel. This software almost does it... if you could be sure you were at the same temp all the time it would probably be trivial to turn its "VE" table (which is really a g/s table) into the real thing.
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Old 01-23-2009, 09:07 AM   #5
MartinSTi05
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Is there a temp correction anywhere in there? neat stuff.
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Old 01-23-2009, 09:10 AM   #6
the suicidal eggroll
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Quote:
Originally Posted by 3rdangle View Post
The objective is to make it easier to calculate an operating point for a new compressor, given a compressor map.
I think this would be much more useful as a VE equation, personally

VE = 5660*CFM/(L*RPM*(psig/psia+1))
your equation gives you CFM from RPM and psig, so with a few little modifications it could give you VE instead.
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