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I am running the calcs for my programming and I have a question- My calcs
are showing that 550 injectors may not be sufficient- here is what I came
up with so far- correct me if I got it wrong-
Our effective displacement is 1.3 liters per rotor- 2.6 total per
revolution.
Mass/ Density of air at 20 deg C at 1 ATM is 1.204 kg/M3
I used 14.7:1 standard ratio of fuel/air for starters- these numbers tell
me that at 100% VE I will go through 23.475 kg/min of air.
That equates to 1596 gm of fuel/min at 7500 rpm. I have not figured in the
increased air from the 8psi boost that I am planning.
The stock 550 injectors are shown to be capable of 395.6 grams// min and I
am going to run 4. This equates to 1582.4 grams /min from all 4 injectors
maxed out. My math says that without a turbo but at 100% VE these are not
enough.
1. Do I have the displacement wrong?
2. Are any turbo guys having issues with lean mixtures at higher boost?
3. Do I need bigger injectors or an additional pair of injectors?
Kevin Alderman
It always helps to have more injectors as you get a more precise setting
with 8 bit
tables and a wider dynamic range. That is why the stock RX8 engine has 3
per rotor.
Paul Lamar
Kevin,
I think that your volume calculation of air per minute is 4 times too high
considering one rotor.
The chamber displacement per rotor is 650 cc, and one chamber is displaced
once per rotation.
Cals: 0.65L * 7500 rpm/min /1000 *1.204 kg/ m^3 = 5.87 kg of air throughput
per 7500 rpm per rotor at 100 VE.
For two rotors the total fuel is to be based on twice that.
Rolf
5.87 Kg times 2.2 pounds per rotor is 12.9 pounds per minute.
A p-port VE is 120% as well. It is more like 30 pounds per minute for a two rotor.
BTW Kevin, I am using a mass air flow sensor so the software does not have to
compensate for intake air temperature. That is automatically done by a mass air flow
sensor.
A Mazda RX8 MAF would work fine as well as any other 250 HP engine MAF. I think they
are all hot wire type now a days. The old 2nd gen turbo was only good for about 200 HP.
http://www.carpartswarehouse.com/addtocart/2009_Mazda/RX8/Mass_Air_Flow_Meter/49-00152.html#
About $80.
They out out 0 to 5 volts so if you feed that through a pot on the instrument panel
you can lean the engine.
Paul Lamar
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