Table of Contents
Genboard can be used in speed density or Alpha-N mode.
Speed density is normally used on stock (or near stock) engines. It is very reliable and very accurate, in some cases however Alpha-N is better.
Alpha-N is useful for long duration cams where the resolution of manifold air pressure (MAP) sensor would be small. It is also useful to get smother idle on engines that have erratic map values.
VEMS support both methods and it is even possible to mix them. It is recommended that speed density is used at first as it is more forgiving than Alpha-N. Alpha-N mode requires experience, very good and repeatable TPS sensor and much patience. The j[] table will be very different compared to speed density mode. Also, don't drive in the mountains (or accept richer mixture) without good EGO correction setup, because Alpha-N mode does not use the MAP sensor.
The properties of Alpha-N can be controlled with the variables listed in Table 11.1, “Alpha-N config variables” .
| Variable Name | Starting point value | Units | Description |
|---|---|---|---|
| hybrid_rpm_a | 0x00 | [100 RPM] | Use Alpha-N (TPS) below this RPM |
| hybrid_rpm_m | 0x00 | [100 RPM] | Use Speed density (MAP) above this RPM |
| config13 | 0x00 | See Table 11.2, “Bitpattern, config13” |
Table 11.1. Alpha-N config variables
| Bit | Name | Description |
|---|---|---|
| 0 | Oddfire | 0: Normal, 1: Oddfire |
| 1 | O2 Sensor | 0: Narrowband, 1: Wideband |
| 2 | Control Strategy | 0: Speed density, 1: Alpha-N |
| 3 | Baro Correction | 0: off, 1: on |
| 4 | Unused | |
| 5 | Unused | |
| 6 | Unused | |
| 7 | Unused |
Table 11.2. Bitpattern, config13
Example setups
Speed density across the whole RPM range:
Alpha-N across the whole RPM range:
Alpha-N below 3200 RPM, speed density above 4800 RPM and hybrid between:
Alpha-N setup - note: WBO2 enable bit is also stuffed in config13 for historical reasons.