[s-cars] Math quiz: turbo compressor choices
MLP
mlped at qwest.net
Thu Mar 11 10:58:00 EST 2004
-----Original Message-----
From: MLP [mailto:mlped at qwest.net]
Sent: Thursday, March 11, 2004 8:47 AM
To: 'Djdawson2 at aol.com'; 's-car-list at audifans.com'
Subject: RE: [s-cars] Math quiz: turbo compressor choices
Dave, have you seen this suggested formula / method for estimating
volumetric efficiency?
VE=(792001.6*(RWHP/0.83))/(RPM * Displacement in in3 * AP * CR)
Where:
VE = Volumetric Efficiency (Theoretical)
RWHP = Rear Wheel Horse Power
Displacement in in3= Engine displacement in cubic inches (2.0L =
122 in3)
AP = Atmospheric Pressure (~14.5 psi depending on altitude)
CFM=(122*RPM*VE%)/3456; and finally
CR = Compression Ratio (Static is close enough)
* The better the information plugged into the formula the more accurate
the output.
Conversions: Lbs/min = 0.0756 x CFM
taken from http://www.320i.com/turbocharging.htm on selecting a coldside
for running an aftermarket boosted 10psi 2.0 (122" c^3) BMW motor? He
comes up with some pretty high VE estimates (105% at 4,000 to 4,500 rpm)
for the naturally aspirated version of an M10 motor, with the lowest VEs
used being 83% at 2,500rpm and 85% at 6,500.)
2nd, I've heard the accuracy of the generic Turbonetic's maps questioned
from time to time. This particularly applies to the "super" trim
series, which to my eye at least, appear to be copies of the equivalent
"regular," i.e. the "non-super" T04E wheel trim maps, moved @ +10 lbs to
the left on the x axis. I've never seen one of the "super trim"
compressor wheels, but from the Turbonetics catalog etc., my impression
is that the difference is reflected in a uniform increase in the inducer
major diameter, from a TO4E's standard usual 2.950" to the "super-sized"
trims 3.200" From Turbonetic's 2001 catalog the various dimensions are
given as:
TO4E Std Trim/Shaft Big Shaft Super TO4E Innovative
Trim Minor Major Minor Major Minor Major "Quill" diam
40 1.870 2.950 same same 1.870 3.200 .250"
42 Innovative but No Turbonetics listing same
44 " same
46 2.003 2.950 same same 3.200 .250 & .312"
46 2nd Innovative 46 version .312"
50 2.122 3.000 2.122 3.00 2.122 3.200 .250" & .312"
50 2nd Innovative 50 version .312"
54 2.170 2.950 same same 3.200 .250" & .312
57 2.230 2.950 same same 3.200 same
60 2.290 2.950 same same 3.200 same
The interesting excepton/varriation in the group, if it isn't a typo, is
the "standard" 50 trim's seeming deviation from the "norm" placing
somewhere between the 2.95 and 3.200 diameters ~ While 5/100ths of an
inch doesn't sound like much, +1.27mm in diameter does seem more
substantial. Not sure what the "Quill" diameters provide by Innovative
refer to, probably the shaft size, and if that's the case, Turbonetic's
offers a standard (.250") and big shaft (.312") versions too.
The catalog doesn't provided any data on the "height" of the wheels, so
I assume they're all equally "tall." That could be a faulty assumption.
WRT to the "compressor" maps, & if someone knows different, please
correct me, I believe each of these "trims" in essence comes from the
same wheel casting, i.e. the wheels all have, for example the same
number of blades, at the same pitch and orientation etc. The casting
blanks are just sized big enough so that they can be machined to the
above different sizes. Now what I was told was the turbonetics
"published" compressor maps are not Garrett's "original" engineering
maps, but rather derivatives. The story goes that in the "way back when
days...." which I assume must have been before computerized data
acquision software etc., a manufacture may have only created one, or at
the most a couple of actual "testing" data based compressor maps for a
ny one particular family of wheel (i.e. the TO4E), the rest of the maps
would be an extrapolation of data based on the original master map or
maps for the compressor wheel.
So, what is a "super" trim TO4E wheel? Is this an "official" Garrett
trim, or something Turbonetics, based on its own in house engineering
work has built off of a standard Garrett wheel? And if its the latter,
how much "extrapolation" was/is required to come up with the map on
which you're asked to base a wheel selection? Is the "super" trim sort
of a Turbonetics trademark/feature, or are other 2nd tier turbo
manufacturers, i.e. Innovative, TEC in Golden &/or Majestic etc. also
offering the trim as their own? I, just for an example, don't see a
"super" trim category in the Innovative catalog. My guess is they, or
TEC in Golden, could probably machine a blank though to Turbonetics
"super" spec size. Has anyone asked?
Any way, probably more than anyone cares about wheels etc.
HTH
mike
-----Original Message-----
From: s-car On Behalf Of Djdawson2 at aol.com
OK... choosing a cold side for a 2.2...
Here's what I think I know:
2.2 liters, max 7000rpm, pressure ratio is 2.7, efficiency guessed at
85%.
Based on these factors, it looks like these engines could require up to
47lbs/min of air. Reviewing the RS2 compressor map, it appears as if
that turbo is
maxed out at around 33lbs/min of flow. If this is correct, I guess it's
really
obvious why my engine power peaks at just shy of 5k rpm.... that's where
it
would require 33lbs/min. After that engine speed, boost drops off, as
does
power, simply because the compressor can provide no more air.
I've looked over the Garrett options. I've made the following
assumptions: Efficiency is 85% 2.2 liters 7000rpm max 25psi boost at sea
level for a PR of 2.7 47lbs/min is the max required air volume for this
engine at 2.7PR.
Reviewing the maps on the various Garrett choices, this is what stands
out
for me:
"Super T04E-50" looks pretty good. Full boost (25psi) capabilities at
just
shy of 3000rpm with no surge problems. Max flow of 47lbs/min is
possible, but
efficiency is around 60%.
"Super T04E-54" looks like an OK choice, but not as good as the 50 trim.
Full boost at engine speeds below 3700rpm should have surge issues. Max
flow is
a bit short at 45lbs/min, and efficiency throughout looks worse than the
50
trim.
"Super T04E-57" is interesting. Full boost at engines speeds below
4000rpm
should have surge issues. Max flow is great at 49lbs/min, and
efficiency is
high up to 7000rpm... always 65% or better. Looks like a good high end
power
choice.
"Super T04E-60" is also interesting. It can support full boost down to
3400rpm without surge. Max flow is 50lbs/min, and efficiency is about
62% at max
rpm, but doesn't look as good throughout the range as the 50 or the 57.
Those are my observations. Any input, corrections, other factors I
should
consider... whatever, is welcome and appreciated.
Thanks,
Dave in CO
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