[s-cars] RE: Math quiz: turbo compressor choices

[MLP]

Yes, VE in the naturally aspirated BMW site formula proposed at
http://www.320i.com/ is supposed to represent volumetric efficiency for
purposes of choosing an appropriate compressor wheel by working
backwards off a naturally aspirated dyno torque curve for the BMW M10
engine.  I guess somewhere in the conversion volumes of air are mixed up
with, or transposed over ?? lbs or slugs of air.  Yeah, 348% would have
to be a "virtual" engine of some kind.
 
This thread started with Dave was speculating about good, better, best
compressor choices for the Audi motor using a general VE assumption of
85%.
The BMW boys have reverse engineered a set of VE estimates for their
motor that run as high as 105% by working backwards off the torque curve
on a dyno chart.  Audi shouldn't have to take no stinking back seat in
VE guestimates to no stink'n BMW motor, so .... how does one get an
accurate, or at least better estimate of the AAN's volumetric efficiency
across a range of rpm, say @ 2000, 3000 4000 etc? 
 
Eric Fahlgrens Turbo Calculator (
http://not2fast.wryday.com/turbo/glossary/turbo_calc.shtml#pr ) allows
independent assumptions to be used for VE while applying different boost
inputs and computing flow in both CMF and by lbs.min. e.g. 
 
                                                    Lands "just short
In                     Sea
                                                      of Everboost
Everboost            Level            Everboost
Ambient Air Temp             15°C
Altitude                               0                5,280 ft
@ 7,100+        
Compressor Efficiency      75%
Manifold Boost                  25 psig
Intercooler efficiency        75%
RPM                                7,000
Volumetric Efficiency        85%
100% 
***************
Pressure Ratio                  2.74          3.11
3.25                      2.74                 3.26
CFM flow                          569 cfm     637 cfm                664
cfm                670 cfm          781 cfm
Lbs/min air flow                 43.5 lbs     40.1 lbs/min
39.03 lbs/min         51.24 lbs/min   46 lbs/min
 
I guess the question remains, what is the AAN's VE at various rpm
points.
 Say at (a) at 1psi of boost; (2) at peak torque @ 4,000 rpm; and the
motors 7000 rpm redline.
 
mike
  

-----Original Message-----
From: FvAMI at aol.com [mailto:FvAMI at aol.com] 
Sent: Sunday, March 14, 2004 1:06 AM
To: mlped at qwest.net; Djdawson2 at aol.com; s-car-list at audifans.com
Subject: Re: [s-cars] RE: Math quiz: turbo compressor choices


In a message dated 3/12/04 7:49:09 AM Pacific Standard Time,
mlped at qwest.net writes:



Even so, a VE claim of 348% seems pretty high, ... and it gets higher if
you bump up the driveline loss adjustment (.83), i.e. 361% at 80% etc.





I assume VE is Volumetric Efficiency!

If so ... I believe the VE (Volumetric Efficiency) is independent of
boost by definition ... I assume you guys are trying to calculate a
"Virtual" VE ... which could be defined as VVE.

So with a Ve of 83% and 2.5 bar absolute pressure the VVE = ....

I think we could claim our 2.2 liter engines have a "Virtual"
displacement of 5.3 liters at 2.5 bar absolute ... but claiming it had a
5.3 liter displacement would be incorrect.

Best regards,
Feico van der Laan