Re: Turbo CFM- calculations for the archives

["Gaidos, A." <agaidos@got.net>]

 Hi Scott,
 A little off topic here but we've been talking about "creating" a
supercharger kit for the n/a 20v on the 20v list. Can I apply similar
equations to figure flow of a supercharger. Please except my apologies if
that's a silly question.
 I ask because I want to know if a G60 supercharger can be used on the 5
cylinder. New Dimensions says no, not enough flow for anything over 2.0L to
be worth it. If the 2.3 L n/a 20v is drawing in more then the G60 can
pressurize then they're certainly right.
Thanks
Anton

-----Original Message-----
From: QSHIPQ@aol.com <QSHIPQ@aol.com>
To: quattro@audifans.com <quattro@audifans.com>
Date: Tuesday, October 05, 1999 4:04 PM
Subject: RE: Turbo CFM- calculations for the archives


>Mr. Fawcett writes:
>>Hey everyone.  I looked in teh archives for this, but had no luck.  My
>>question is, what amount of cfm is the k26 turbo capable of producing?  Or
>>is it a better question to ask, with 20psi in the intake manifold, how
>>many cfm is the k26 producing?  This is on a 10v I5.  Any idea where I
>>could find this out?
>>Thanks, as usual.
>>James Fawcett
>>86 5kTQ
>
>James:
>I thought I posted this once, but thanks for searching first.  Here's how
you
>can figure engine cfm and turbo map stuff (and I'm not giving away my store
>here, basic information only).
>
>2.2liters = 134ci
>134 * rpm/1728 * 2 = 134*5500/3456
>= 213CFM @ 5500 rpm NORMALLY ASPIRATED
>213 * PR = AIRFLOW RATE (approximate, but maximum, figured at 100%
Volumetric
>Efficiency - I usually use 80% for the 10v cars, 85-87% for the 20v cars.
>The actual calculation to get to the above:
>cid * rpm*0.5* VE/1728
>**  Note: most tuners choosing turbos use the above calculation without VE
to
>help them account for altitude compensation)
>
>PR = Po + P1/Po, let's assume sea level
>First convert psi to bar:
>20psi + 14.7/14.7= 2.36bar absolute so,
>2.36bar - 1.0 bar (atmospheric) = 1.36 boost pressure
>
>PR = 1.0bar + 1.36bar/1.0bar
>
>Pressure Ratio = 2.36 (not a futile exercise for those above sea level:)
>
>Back to AIRFLOW RATE
>2.36 * 213 = 502.68CFM
>
>PROBLEMS:
>*  A two pass IC can only flow about 400CFM thru it's core in *single* pass
>trim
>*  A 2.36PR on a k26 turbo is outside both the k26 turbo map in terms of
>speed (that's 120,000rpm+++) - fyi, KKK doesn't list speeds higher than
that
>on just about any turbo they make
>*  You are just at 60% compressor efficiency (peak in stock trim is 72%)
>*  A stock 10vt k26 doesn't put out 500cfm
>*  RULE TO REREAD:  Turbo speed alone doesn't increase flow, it increases
the
>pressure ratio
>*  Bottom Line:  Wrong turbo to be running 2.36PR
>*  Next rule of thumb on I5 10vt:  Density rules over boost pressure.  Take
a
>ride in a 5ktq with a big effiecient intercooler @ 15psi boost, you'll
forget
>about more boost.
>
>To begin your journey into the black magic of turbochargers get:  Maximum
>Boost by Corky Bell, it's a great baseline, and some insurance against
doing
>something silly.
>
>For those so inclined to do the math, figure 2.0 maximum PR on a stock k26
>audi 10vt turbo car, 5700 maximum rpm cfm, 80-85% VE depending on mods, 65%
>minimum compressor efficiency .
>
>
>HTH
>
>Scott Justusson
>QSHIPQ Performance Tuning
>QSHIPQ@aol.com
>
>
>