Fueling

Race Core fuels with speed-density: MAP × VE × req-fuel, then corrections (CLT, IAT, voltage/dead-time, ethanol, accel). Get req-fuel and dead-time right or the VE table will be a compensation chart for a maths error.

Required fuel

Req-fuel is the pulse width that would achieve stoich at 100 % VE, 100 kPa, your injector size, your displacement. TunerStudio can calculate it if you enter:

• Displacement and cylinder count
• Injector flow at the base fuel-pressure you actually run
• Stoich AFR (14.7 petrol, ~9.8 E85, blend if flex)

Then do not keep editing req-fuel to “make it richer.” That is what VE is for. If idle VE wants to sit at 30 % or 80 % on a sane engine, req-fuel or dead-time is wrong — fix those, reset VE to a reasonable 40–55 % idle and start again.

Dead time

Injectors do not open instantly. Dead-time vs battery voltage is a table, often 0.6–1.2 ms at 14 V for a modern saturated injector, more at 10 V. At idle the dead-time can be half the pulse. A 0.3 ms error is a 20 % fuel error at 1.5 ms PW. Use the injector manufacturer’s table, then fine-tune so AFR does not jump when you turn fans and lights on.

VE table

• Idle: get it to target AFR first. This is your sanity cell.
• Cruise: 30–50 kPa, 2–3 k rpm. Tune to target. This is most of the street map.
• Transients: accel enrichment (TPS or MAP based) covers the hole while the wall wets. Do not put a giant spike in VE to hide a missing accel term.
• Boost: tune on a dyno with the wideband, one cell at a time. Do not copy a 1.5 bar column into 2.0 bar and hope.

Closed loop

Enable when open-loop AFR is already within about 0.8 of target in that area. Authority should be modest (±10–15 %) so a failed wideband cannot command a 40 % lean-out. Long-term trims are a diagnostic — if they grow past a few percent in a cell, fix VE.