Subject: 20B turbo...calcs Air Density at Sea level.
From: ACRE NL
Date: 9/10/2002, 7:20 PM



Paul,
I have attached a dyno chart for the turbo 13b you posted

earlier

(exhaust

manifold pic) from Paul Yaw's web site.  The chart indicates it
is  producing 262 hp at 6500 rpm with 6.4psi boost, flowing

405cmf.

From

this information, could I deduce that a similarly prepped turbo

20B

would

flow 607.5 cfm (405 x 1.5).  Since I won't be running quite that

high of

rpm's, I figure I could reduce this figure by about 10%, to

about

550cfm,

assuming the dyno chart is accurate.

As for the specifics for the above engine:  "The turbo (From

Turbonetics)

is a Garrett TO4E, 50 trim compressor, P trim exhaust, with a

modified 1.3

AR ratio housing. The turbine wheel is made of inconel. The

center

section

is water cooled. The turbo feeds the engine through a small

intercooler

made by Spearco.  Boost is 6.4 psi at 6500 rpm. (43" Hg.

manifold

pressure.)


How do I convert cfm to lbs/min to use in the turbonetics chart

and

maps?

Thanks,
Mark



Air density at sea level is about  .0019 pounds per cubic foot.
So CFM X .0019 = pounds/min

Paul Lamar




Paul,
Sorry to be so dense (no pun intended) on this, but if I multiply

this

out

I get 405 * .0019 =  .7695.  This doesn't appear to match with the

turbo

selection chart.  Could the "lbs/min" label be wrong?  Should the

chart

be

labeled lbs/hr rather than lbs/min?  As in,
.7695 * 60 = 46.17 lbs/hr, which looks like it would match with the

chart

for a 13B.    This comes out real close to where you drew the lines
for  the 13B.

Mark



Could be an error.
Paul Lamar



Air at STP=.08071 lb/cf, at 59F=.07651 lb/cf.
405 cf=32.7 lbs/min
[Marc Wiese]


Right you are Marc and Mark. I mis-read that chart. The density curve is displaced to the
right. Curious! Sorry! At 59 F, 15 C, 29.91"Hg  it is .002378 slugs/cubic foot. 

Or 32.17405 X slugs or .07651 pounds per cubic foot. 

Paul Lamar
 
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