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