I attempted 3 times to post the new spreadsheet to the
list, but it is a few KB too large. So those of you who may want it, send
me an e mail to eanderson@carolina.rr.com with the
subject : Spreadsheet . I will send you a copy.
Details of latest revisions.
In the past, I have provided a spreadsheet to aid in
determining power, fuel flow, heat produced, etc, and have also attempt to
provide some rudimentary cooling calculations. You can entertain yourself
with it as well with your dream engine {:>)
Since there was no engine load component in earlier
spreadsheets, I had provided % throttle opening factor as a
substitute. However, that was never satisfactory because who of
us know exactly what % throttle opening we have at any point and besides
that throttle opening does not necessarily correspond to load.
In any case, I recent revised the spreadsheet, so that a
user may now put in his manifold pressure. That is generally a parameter
available to most folks. It also eliminates potential errors from
altitude, air density, temperature etc. It and rpm also provide a
better indicator of LOAD than does throttle position. It will also
works for N/A and turbo engines.
All you do is enter your manifold pressure (and
the other engine operating parameters) and the calculations will use
that to calculate the air density in the intake and from that the power, flow
rates,BTU, etc. So now the manifold air density is separate from the
cooling air density which is dependent on altitude. So manifold pressure
and altitude (ambient pressure) are now separate for engine operation and
cooling operations.
So in the cooling section you must now enter your altitude
for cooling calculations. Also, I have now provided for the user to enter
the dimensions of his cooling cores and the number rather than the default Gm
cores and RX-7 oil cooler I had been using. You can change these
parameters on the second sheet titled "Cooling Calculations", it shows
recommended default values (the GM cores and Stock Rx-7 cooler) just to get you
started or if your project is still in the dream stage.
Also there is provision on the cooling calculations sheet
to have your coolant flow rate proportional to engine rpm (more
realistic). The flow rate is based on Racing Beat information for 1974 and
later coolant pump flow rate. If you have changed the pulley ratio
to non-stock then these flow rates may be off a bit - but still more realistic
than assuming a 40 gpm flow rate at idle and at 6000 rpm {:>).
So these changes mean you can now simulate a partial
throttle operation say at 19" Hg and a cooling altitude at 7500 MS. You
can now see if your system should be cooling at that power setting and then you
could change the power setting to 22" Hg and see if you installation should
still cool at that selected air speed and altitude and power setting.
Manifold pressure and Air Fuel Ratio can make a considerable difference in the
amount of heat produced. So pay attention to the values you are
using.
Now here is the potential problem I can see. If you
tell the spreadsheet you are flying at 7500 MSL in the cooling data input, but
you decide to use WOT for your engine, you must realize that the ambient
pressure (and therefore your manifold pressure) at that altitude will not
be 29.92 " HG. Your manifold pressure (for N/A engine) would
never be that high for an N/A engine at that altitude - but, it
could be for a turbo engine. So unless you selected YES for turbocharged in the data entry area, an
error message will be displayed "Manifold Pressure
exceeds ambient". It can also happen if you have already
selected a manifold pressure say 29" while at sea level, but then you enter 2000
MSL for altitude in the cooling section. The warming message will
inform you that your manifold pressure now exceeds the ambient pressure at
2000 MSL ( unless you enter
turbo charged = "yes").
If you select an RPM value for the cooling section and it
is outside the limits of the rpm values in your calculated data
table, then an error message "Invalid
RPM" will be shown in the cooling data entry area. So that
would mean either change the rpm OR change the range of rpm in the table by
adjusting the rpm start value or the rpm step value.
As always, if anyone finds an error or problem please let
me know.
Ed