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

[MLP]

Dave - the suggested formula for calculating VE and the cfm to lbs/min
constant came directly from 
the www.320i.com   ~>  <http://www.320i.com/turbocharging.htm>
www.320i.com/turbocharging.htm  page.
 
I've sent your question on the email address listed at the site.  Let's
see if the author has enough interest to reply. 
I'm assuming the 0.83 figure/constant in the BMW site's suggested
formula is a drive line conversion factor for changing the dyno chart to
flywheel hp.
What number are you going to use?
 
Mike

 -----Original Message-----
From: Djdawson2 at aol.com [mailto:Djdawson2 at aol.com] 
Sent: Thursday, March 11, 2004 9:45 PM
To: mlped at qwest.net; s-car-list at audifans.com
Subject: Re: Math quiz: turbo compressor choices



Mike,
Based on your info, I get:
VE=(792001.6*(325/.83)/(4800*135.8*14.7*9.3)

This doesn't make sense...  3.4ish....?

I based it on my dyno run, and input the rpm figure where that
horsepower figure was developed.  What am I doing wrong?  I used 14.7
for AP, as the dyno figures were corrected to sea level. I used 135.8
for the displacement (61.02*2.226).

Also, where did you get .0756 as your conversion figure for CFM to
lbs/min?  I generated mine by calculating the molar mass of breathing
air (28.9gm/mole), then converted liters to cubic feet... 1l = .0353147
cubic ft, so 1 mole (22.4 liters) of air = .791 cubic ft.  Therefore,
one cubic foot of air has a mass of 36.54 grams (28.9/.791).  Divide
that by 453.6 grams/lb, and I got .0806...  granted, only a 6.5%
difference, but I'm curious where your number came from, and if it is
more appropriate for these calculations..
Thanks for the info.
Dave