Gordon C. Alling, Jr., PE

President

acumen Engineering/Analysis, Inc.

540-786-2200

www.acumen-ea.com

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

Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com