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Rick Schrameck's supercharging system sounds promising, however, I doubt
that Rick will be able to forgo intercooling at altitude. On the other hand,
at the risk of going down in flames, I disagree with some of the statements
by Jack Kane.

Jack suggests that Rick's reported numbers are the result of faulty
instrumentation. I suggest that they are within the realm of reasonableness.
This thread prompted me to create a spreadsheet that calculates the
Compressor Outlet Temperature for a given altitude, Manifold Absolute
Pressure, Outside Air Temperature, and Compressor Efficiency. The formula
was derived from several reference sources and suggests that on a 63 degree
day in Las Vegas a supercharger with 75% efficiency could produce 41.8" Hg
Manifold Absolute Pressure ("MAP") at a temperature of 150 degrees. This
results from using a calculated Pressure Ratio ("r") of 1.51 and an ideal
gas constant ("Y") of 0.1237.

In addition, extrapolating the performance curves for the IO-550G (a long
way into uncharted territory) , suggests that Rick's engine might have been
producing 350 HP with a Brake Specific Fuel Consumption ("BSFC") in the
range of .69 pounds of fuel per HP per hour, very close to the 0.7 figure
that Jack said was required to prevent detonation in his posting in issue
#347. By way of comparison, TCM's stated BSFC for the TSIO-550-B at 350 HP
and 35" Hg MAP is 0.715.

Therefore, I believe Rick's data for his ground run are fairly accurate.

If we now turn to the system's performance at altitude, the need for an
intercooler becomes painfully apparent, at least if Rick tries to maintain
40+ " Hg. I will present the expected results in the table below expressing
temperature in degrees Fahrenheit (and I hope the formatting translates OK):

Compressor Outlet Temperature at 40" Hg MAP vs. Altitude at Standard
Conditions
Altitude   Temp    OAT      r          Y
5000'        137       41      1.61     .144
10,000      157       23      1.94     .207
15,000      177         6      2.37     .276
20,000      198      -12      2.91     .352
25,000      220      -30      3.60     .437
29,000      238      -44      4.29     .510

As you can see, there won't be any icing problems in these intake runners!
Furthermore, few compressors, whether driven by an exhaust gas turbine
(turbocharger) or by a belt or gear drive from the engine (supercharger),
can exceed a Pressure Ratio ("r") of 3.0 and still maintain acceptable
efficiency, i.e. greater than 70%. Therefore, I do agree with Jack that
there must be a suspension of the Laws of Thermodynamics when Rick's
proposed system is flown up in the flight levels.

Alternatively, If we set an upper limit of 150 degrees for the Compressor
Outlet Temperature and keep r at or below 3.0, Rick's system can still
produce respectable performance as shown in the following table:

Compressor Outlet Temperature and MAP vs. Altitude at Standard Conditions
Altitude   Temp   MAP   OAT      r
Sea Level  129      42      59     1.40
5000'         148      42      41     1.69
10,000      145       38      23     1.85
15,000      148       35       6      2.07
20,000      149       32     -12     2.32
25,000      148       29     -30     2.61
29,000      150       27     -44     2.90

Note that the last row corresponds to the Maximum MAP in cruise recommended
by TCM which translates to 240 HP at 2450 RPM.

The last table above still represents respectable performance figures, but
only if we ignore such factors as heat rejection requirements (engine
cooling) and engine reliability both in the short term at the higher MAP's
and in the long run in regards to whether the engine can achieve 2000 hours
without a catastrophic failure or a significant degradation in performance
due to ring blowby or top-end problems. Dare I say, "Only long-term testing
will tell"?

I will try to figure out how to post the Excel spreadsheet to the attachment
area of the list for those of you who wish to play with the numbers and/or
verify my formulas.

Regards,
Mike Hutchins


[Just send the attachment to me in a private email and I'll get it placed
on the site.     <Marv>]



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