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01-22-2009, 02:10 AM | #1 |
Scooby Newbie
Member#: 142335
Join Date: Mar 2007
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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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01-22-2009, 02:48 AM | #2 |
Scooby Guru
Member#: 140444
Join Date: Feb 2007
Chapter/Region:
NWIC
Location: Near Seattle, WA
Vehicle:05 Stage Free LGT ATP 3076, 6MT, AVO FMIC |
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? |
01-23-2009, 02:23 AM | #3 |
Scooby Newbie
Member#: 142335
Join Date: Mar 2007
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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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01-23-2009, 02:36 AM | #4 |
Scooby Guru
Member#: 140444
Join Date: Feb 2007
Chapter/Region:
NWIC
Location: Near Seattle, WA
Vehicle:05 Stage Free LGT ATP 3076, 6MT, AVO FMIC |
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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01-23-2009, 09:07 AM | #5 |
Scooby Specialist
Member#: 145145
Join Date: Apr 2007
Chapter/Region:
MWSOC
Location: Rockford, Il
Vehicle:2006 wrx STi |
Is there a temp correction anywhere in there? neat stuff.
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01-23-2009, 09:10 AM | #6 | |
Scooby Guru
Member#: 51961
Join Date: Jan 2004
Chapter/Region:
RMIC
Location: Broomfield, CO
Vehicle:2005 STi 2012 WRX |
Quote:
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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