Ok, folks
Here is a spreadsheet I spent quite a bit of time
building and improving. The power section I feel very confident in, the
cooling section less so - just too many variables that vary considerably from
one installation to another. The engine on the other hand is the engine
and less variation between installations.
I do believe this can give you a useful tool for "what
ifs" in planning your installation and even better for inputting actual engine
data and getting estimates of what your power, fuel burn and heat rejection
requirements are.
This is offered as an Educational tool, no warranty
exists or is implied {:>). The user accepts full responsibility for
its use and consequences.
The spreadsheet is divided into two basic
components. The Power section and the Cooling section.
Power Section:
Attached is a spreadsheet that can provide an
approximation of your engine's performance. In addition, it provides the
HEAT in BTU that the coolant and oil system must get rid of. You can
change rpm, A/R ratio, manifold pressure, OAT, number of rotors and gearbox
ratio - any white cell on the spreadsheet surrounded by bold blue boarders can
be changed.
At one time the spreadsheet tried to take input data on
your induction system (such as throttle body size, length of duct work, size
of runners, etc) - however, that just turned out to be pretty useless as
every induction system varied so much and some of the calculations got pretty
esoteric {:>)
I finally realized that manifold pressure accurately
represented the effectiveness of any induction system (regardless
of how unique{:>)) and most folks had a manifold pressure gauge, so
that change to the spreadsheet make it considerably more accurate and
useful. You can even input Turbo manifold pressure, but be sure to
change the "TURBO" block from NO to YES.
Cavet:
Remember this is NOT a simulator - in
other words, the values are not conditional on engine load, another variable
which is just too hard to try and quantify for each installation. So
these calculations are based primarily on fuel flow and engine rpm
and assumption that the engine can operate at the rpm you are interested
in. In other words, you can get this spreadsheet to show your are
producing 450 HP at 9000 rpm, but it ain't gonna happen in the real world with
any meaningful prop load on you engine. You can easily hit 9000 plus
rpm without any engine load and a few folks have done it - and have
scattered parts of gear drive and engine into garage walls,
etc.
Now if you are using the spreadsheet and inputting
actual performance data from your engine installation then the results are
believe to be within 5% for the power section.
Concept:
Basically you select the number of rotors which
will limit the maximum airflow through the N/A engine. The
volume of the rotors and manifold pressure you input then determines the
airflow through the engine for each rpm. IF you then select the
Air/Fuel Ratio, that tells the spreadsheet what fuel flow must be
provided to match the airflow to give your selected A/R. This
combination is then used to calculate the heat content of the fuel burned (in
BTU units), from that total energy, allocations for mechanical power, coolant
heat and oil heat and exhaust are made. Various other parameters
are derived from these basic calculations and converted to common parameters
such as Fuel Flow in Gallons Per Hour, Heat rejection required in BTU, etc.
Other parameters such as prop torque and rpm are again
derived from these calculations and your input of gear ratio,
etc.
The spreadsheet is protected and no, I won't unprotect
it. Years previous, I did send out unprotected spreadsheets and
well\-intended folks changed some of the formulas and relationships which (in
my opinion invalidated the spreadsheet) and then distributed them with my John
Hancock still attached.
You can extend the rpm range by changing its starting
point or by changing the interval from 100 to something different.
Likewise, you can play with intake temperature and Air/Fuel ratio to see how
much effect those parameters have
Cooling Section:
There is also a cooling segment that never got to the
point I had intended. Its based on radiator surface area and airflow
required to get rid of the heat your engine is generating. The oil cooler
is based on the stock Mazda - so compare your oil cooler surface are to
the stock Mazda and adjust by that ratio. In other words, if you have a
stock Mazda you should enter "1" if your oil cooler surface are is 1.5 times
that of the stock then enter 1.5 For the radiator use the frontal
area of your radiators, in my case I have two GM cores each with a 9x10"
frontal area (not counting side tanks), so I input the surface area of one and
input 2 radiators of that size. You could just as easily taken the 90 sq
inch and multiplied by 2 = 180 and then input that and "1" radiator. The
main thing is to input the correct frontal area. Clearly this
section is based on assumptions about ducting effectiveness and other system
unique variables which are certainly different in each installation and
therefore this section is not considered as valid as the power section - but,
it does give a ball-park indication.
You need to input the airspeed and rpm that you
want to check cooling at. The spreadsheet will then check your power
figures by selecting the BTU figures at the rpm you entered in the cooling
section - so the power calculations portion of the spreadsheet must cover the
operating conditions (primarily rpm) of your engine. If you select an
rpm in the cooling section that was not generated in the Power section you
will get an "Invalid RPM" message.
The key factors in the power section are rpm, Air/Fuel
Ratio, Manifold pressure and Temperature. You can change the number of
rotors 1,2 or 3 and gearbox ratio.
No claim of accuracy is made - just a tool to assist you
to get some ball-park figures on your engine project.
Enjoy
Ed