Fueling & Ignition

Deliver the right mix, fire it clean.

Fuel system capacity and ignition stability are the backbone of every build. Here’s how to size injectors, choose pumps, set AFRs, and keep spark reliable — whether NA, boosted, or flex fuel.

1) Injector sizing & flow

  • Stock NC injectors: ~310cc (good up to ~200 hp NA).
  • 400–600cc: Stage 2 NA or mild boost.
  • 750–1000cc: Turbo builds 300–450+ hp.
  • EV14 injectors are industry standard (linear, fast response).

Rule of thumb: Injector duty cycle < 85% at peak load for safety margin.

2) Fuel pumps

  • OEM pump ~120–130 lph → enough for stock or mild NA.
  • 265 lph → common upgrade for Stage 2/3 NA or small turbo.
  • 340 lph (Walbro/Ti) → recommended baseline for boosted builds.
  • 450 lph → E85/high hp turbo setups.
    • Tip: Voltage and wiring matter. Weak supply drops flow — log pump duty/voltage if trims go lean under load.

    3) AFR / Lambda targets

    NA

    • Cruise: ~14.7 AFR (λ 1.0)
    • WOT: 12.8–13.0 AFR (λ 0.87–0.88)

    Turbo

    • Cruise: ~14.7 AFR (λ 1.0)
    • WOT: 11.5–12.0 AFR (λ 0.78–0.82)

    Exact AFR depends on fuel, turbo efficiency, and knock feedback. Always tune on wideband.

    4) Ignition system

    Spark plugs

    • Stock NA: OEM heat range 6.
    • Turbo/track: one step colder (NGK 7).

    Coils

    • NC coils are fine until ~300 hp; higher → upgrade or check dwell maps.
    • Log spark energy and misfire counts under boost.

    Dwell & timing

    • Respect coil saturation time; avoid excessive dwell = heat failure.
    • Ignition advance must follow knock threshold, not “internet maps”.

    5) Ethanol / Flex Fuel

    • E85 has higher knock resistance → more timing, more boost potential.
    • Requires ~30% more fuel flow (injector + pump sizing critical).
    • Flex fuel sensor allows real-time blend compensation (BoostIT Pro or ECU input).

    Ethanol quality varies. Always confirm content with a tester — don’t assume pump E85 is 85%.

    6) Common issues

    Lean under load

    • Fuel pump maxed or low voltage supply.
    • Injector duty >95% → upgrade required.

    Misfire at boost

    • Plug gap too wide → close gap (0.6–0.7 mm for turbo).
    • Weak coil or incorrect dwell mapping.

    Knock activity

    • Too much timing advance.
    • High IAT/ECT; intercooler or cooling insufficient.
    • Low octane or inconsistent fuel quality.

    7) FAQ

    Do I need bigger injectors for a 2.5 NA swap?

    Not always. Stock injectors are fine until ~200 hp. With cams or aggressive maps, 400–600cc gives safety margin.

    How do I know if my pump is maxed?

    Watch trims & wideband. If AFR leans out at WOT despite correct injector duty, pump is out of flow or voltage is low.

    What AFR should I aim for?

    NA: ~12.8–13.0 at WOT. Turbo: ~11.5–12.0. But final number depends on knock, turbo efficiency, and cooling.

    Fueling or ignition issues? Send us your logs (AFR, trims, misfires) and we’ll pinpoint the bottleneck.
    Ask Yiannis