Skip to main content

SD + Alpha-N Air Mass Blending

Capoworks ECU can combine Speed Density (SD) and Alpha-N cylinder-air-mass calculations in one fuel strategy. Select Fuel strategy > SD + Alpha-N. The strategy uses the existing SD and Alpha-N branch calibrations together; it does not replace either branch's tables or sensors.

What the blend changes​

The SD branch calculates cylinder air mass from RPM, MAP, temperature and the Speed Density table. The Alpha-N branch calculates cylinder air mass from RPM, TPS, temperature and the Alpha-N filling table. The blend decides how much of each calculated cylinder air mass contributes:

blended cylinder air mass =
    (1 - Alpha-N authority) * SD cylinder air mass
    + Alpha-N authority * Alpha-N cylinder air mass

The authority is a percentage. A 0% cell uses SD only, a 100% cell uses Alpha-N only, and an intermediate cell mixes the two cylinder-air-mass results. After that mix, one shared air-mass correction multiplier is applied to the blended mass before fuel is calculated; the correction is not applied separately to each branch or again later in fuel computation.

This is not a VE-percentage blend and it does not blend fuel pulse widths. The existing VE blend tables are separate correction overlays; they do not choose or combine the SD and Alpha-N air-mass models.

Firmware and tune compatibility​

Use the matching generated TunerStudio INI for the installed Capoworks firmware. The layout that contains this feature uses flash data version 20032. Older binary tunes reset under the new layout and are not migrated automatically. Back up the old tune, open it with the matching old definition, and transfer the needed values into the new definition by hand. This includes recreating any former 4x4 cylinder fuel-trim values in the appropriate SD or Alpha-N model family.

Create the authority table​

  1. In TunerStudio, open Base Engine > Base Engine Settings, set Fuel strategy to SD + Alpha-N, and write the setting.
  2. Set up the SD and Alpha-N branch tables and their sensor inputs. A mixed authority region needs both branch results; a 0% or 100% endpoint evaluates only the branch that contributes there.
  3. Open Fuel > SD + Alpha-N blend.
  4. Choose Authority Y-axis source.
  5. Fill in the 8x8 authority table. Its columns are RPM and its rows are the selected authority load. Cell values are % Alpha-N.

The two authority choices have different meanings:

  • TPS % schedules authority from the TPS reading and table breakpoints. This is the firmware default.
  • Measured MAP kPa schedules authority from a valid measured MAP reading and its pressure breakpoints. A MAP estimate cannot authorize the blend.

For measured-MAP authority, the load must be a valid finite measured MAP from 0 through 1000 kPa. If that coordinate is unavailable, the firmware does not schedule the authority table: requested authority is 0%, so it first tries the SD branch, then uses a healthy Alpha-N branch if SD cannot complete. It marks authority unavailable and branch fallback in diagnostics, and the admission state is degraded rather than faulted when a complete branch carries the calculation. A missing authority coordinate alone therefore does not immediately reject the calculation. If both branches fail, admission is closed. A permitted TPS/RPM MAP estimate may serve the SD fallback, but it never becomes the measured-MAP authority-table coordinate.

The authority Y-axis selects how much Alpha-N contributes; it does not retarget either model. The SD branch remains indexed by its MAP/RPM table and the Alpha-N branch remains indexed by its TPS/RPM filling table.

Changing Authority Y-axis source changes the table's units. Review and re-enter the load breakpoints before running with the new source; they are not converted automatically.

The factory-initialized authority table is all 0%, with TPS as its load source. That is only a starting state for a new configuration, not a validated engine calibration or safe operating recommendation.

Calibration requirements​

The blended authority table is bilinearly interpolated, so its axes must meet the firmware's strict checks:

  • The authority load axis has 8 finite, non-negative, strictly increasing breakpoints. It must end at or below 100 for TPS authority or at or below 1000 for measured-MAP authority.
  • The RPM axis has 8 finite, non-negative, strictly increasing breakpoints and must end at or below 18000 RPM.
  • Every authority-table cell must be within 0 to 100 percent Alpha-N.
  • The SD and Alpha-N branch axes must also pass their own strict checks. Their load and RPM breakpoints must be finite and strictly increasing; an Alpha-N TPS axis must stay within 0 to 100, while MAP load axes must stay within their supported range and RPM axes must end at or below 18000.

Invalid axes can prevent a valid composite calculation. Do not repair an axis by duplicating a breakpoint; equal adjacent values fail the strict-ordering check.

Air-mass and idle policies​

Use Fuel > Air mass model settings to select behavior shared by the active air-mass calculation:

  • Air temperature source selects Tcharge or IAT for the physical air-mass calculation. If the selected source is unavailable, the result is marked degraded rather than silently treated as fully healthy.
  • Use MAP estimate table permits the TPS/RPM estimate to serve SD sensor fallback and the optional transient comparison. It does not make an estimate eligible for measured-MAP authority.
  • Alpha-N barometric compensation scales the Alpha-N filling reference by measured BARO. Alpha-N calibration reference pressure records the pressure at which the Alpha-N filling table was calibrated. Review the Alpha-N table and calculated mass after changing either policy.

If the separate idle VE table is enabled, its Idle VE load source controls the idle overlay's coordinate. The choices are Model default, Measured MAP, TPS, or Effective MAP. A missing coordinate for that choice causes idle-VE fallback and marks the affected branch degraded. In blended operation, review the idle policy as well as both main branch tables.

Fallback and diagnostics​

When one contributing branch fails, the firmware may replace the composite with the other complete, healthy branch. It does not use a numeric result from a failed branch. If neither branch is healthy, the calculation is rejected and new fuel admission is closed rather than using a fabricated air mass.

Fallback is a calculation policy, not a guarantee of absolute engine safety. It cannot determine whether the remaining branch's calibration is physically correct for the engine, fuel, sensors or operating condition.

Log and inspect these TunerStudio channels while commissioning and testing the strategy:

  • Air blend: injection admission state shows whether the composite is not ready, ready, degraded, or faulted.
  • Air blend: requested Alpha-N weight and Air blend: effective Alpha-N weight show the table request and the authority actually used after fallback.
  • Air blend: model fault and Air blend: model flags identify the fault class and fallback details.
  • Air blend: SD raw mass, Air blend: Alpha-N raw mass and Air blend: common correction multiplier show the pre-blend masses and the single correction multiplier applied afterward.
  • Air blend: SD branch load, Air blend: Alpha-N branch load, Air blend: SD branch VE, Air blend: Alpha-N branch filling and Air blend: authority Y coordinate show which branch coordinates and table values participated.
  • Airmass: Temperature used, Airmass: Temperature source, Alpha-N: BARO coefficient and Airmass: Temperature/MAP estimate fallback flags expose the pressure and temperature policies.

For decoded numeric logs, Air blend: injection admission state maps to AirmassInjectionStatus: 0 Legacy (not used by this composite strategy), 1 NotReady, 2 Ready, 3 Faulted and 4 Degraded. Air blend: model fault maps to AirmassInjectionFault: 0 None, 1 Configuration, 2 Sensor, 3 Correction, 4 Result, 5 Load, 6 StrategyChange and 7 Scheduling.

Verify that the selected authority coordinate has the expected units, the effective authority matches the request when no fallback is active, and the reported branch masses move consistently with the logged sensors. Do not assume correct fueling from the presence of a numeric gauge.

VE Analyze​

Capoworks ECU qualifies VE Analyze only when the entire authority table is uniformly 0% (SD endpoint) or uniformly 100% (Alpha-N endpoint) for the current running session. A mixed table, branch fallback, active separate idle VE, authority failure, or configuration write during the session removes that qualification until the next actual engine stop. Tune the branch endpoint tables under a qualified endpoint; a mixed authority table is not a VE Analyze target.

Independent load coordinates​

The authority table controls only the SD/Alpha-N cylinder-air-mass blend. Ignition correction, injection phase, staged injection, short-term fuel trim, lambda protection and other load-indexed functions have their own load selectors. Changing the blend axis does not change those consumers automatically. The composite's internal coordinate is effective MAP, but a consumer must explicitly select that or another load source according to its own configuration.

Implementation evidence: blended_airmass.cpp at firmware commit 8f4fcfb.