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