@Charlie: I think all 4 injectors being the same makes sense.
@Steve: Your Glasair looks great! How does she fly?
With that in mind - I may program up my EC3 and EM3 as I own them already and MegaSquirt is expensive and Speeduino seemingly is out of stock and has been for a while.
I have heard from Ross as well that SDS will not support Rotary, but I am not entirely sure I understand why as it is intended to be fully user programmable why would I not be able to program it to work on a rotary just like I would be able to program the MS Pro or Speeduino? Benefit being SDS is supported and designed for aviation.
To understand how a rotary engine works with MegaSquirt® EFI Controller, we need to figure out how MegaSquirt® will 'see' the rotary in terms of injection cycles.
In 720° of crank rotation, a four-stroke cycle piston engine (two revolutions = 4 strokes) ingests its rated displacement (ignoring volumetric efficiency issues and the like) of air. In the same 720°, the rotary swallows twice its rated displacement (somewhat like a 2 stroke cycle engine).
To understand this, recall that a Wankel rotary engine has three faces on each rotor, evenly spaced at 120° apart. The rotors rotate at 1/3 the eccentric shaft speed, so we see an ignition event every 120°Ã—3 = 360 degrees, and all three faces require 3×360° = 1080° of eccentric shaft rotation.
(Note that all of these factors are determined by the geometry of the case, housing, and gears, and are the same for all Wankel rotary engines.)
In the 13B, there are two rotors, however, and they are phased 180° apart, giving an ignition event every 180°, alternating between the rotors.
| Crank Degrees | Piston Engine
Cylinder Firing | Wankel
Rotor Firing |
| 0° | 1 | 1 (face 1) |
| 180° | 3 | 2 (face 1) |
| 360° | 4 | 1 (face 2) |
| 540° | 2 | 2 (face 2) |
| 720° | 1 - back where we started | 1 (face 3) |
| 900° | 3 | 2 (face 3) |
| 1080° | 4 | 1 (face 1) - back where we started |
Therefore, setting up a rotary as a 4 stroke cycle, 4-cylinder (since it gives 4 tach pulses per 720°), and 2600cc (displacement x 2), works out fine. The number of squirts per cycle may need some experimentation for your specific installation, as with any MegaSquirt® installation.