Staged injection data for the 13B rotary family: FC and FD RX-7, RX-8 Renesis, and three rotor 20B. Primary and secondary sizes, feed style, impedance by year, and why rotaries are harder on injectors than any piston engine, compiled by the injector cleaning department at Boost Lab, Inc.
Every injected 13B runs staged injection: small primary injectors handle idle and light load, then secondary injectors come online as load rises. The FD RX-7 runs two 550 cc primaries on the short rail and two 850 cc secondaries on the long rail, all side feed and high impedance. The factory ECU cuts the primary pulse width to roughly 39 percent at the switchover point, so the primary to total flow ratio matters if you ever change sizes on the stock computer.
FC RX-7s are simpler: four top feed injectors, 460 cc on naturally aspirated cars and 550 cc on Turbo II, with impedance changing by year. Early S4 cars ran low impedance injectors, later cars high impedance, so year identification matters before you order anything or wire an ECU.
Rotaries are also uniquely hard on injectors. The engine burns oil by design, runs rich under boost, and secondary injectors can sit unused for long stretches of gentle driving, which lets deposits build until the moment you need full flow. A lazy secondary on a turbo rotary is a lean condition at exactly the wrong time, and lean is how rotaries die.
| Application | Position | Flow | Feed | Impedance | Notes |
|---|---|---|---|---|---|
| RX-7 GSL-SE 1984-85, 13B | All four | 680 cc/min | Top feed | LOW IMP | Early 13B EFI |
| RX-7 FC NA 1986-87 (S4) | Primary + secondary | 460 cc/min | Top feed | LOW IMP | Low impedance years |
| RX-7 FC NA 1988-91 | Primary + secondary | 460 cc/min | Top feed | HIGH IMP | High impedance years |
| RX-7 FC Turbo II 1986-87 (S4) | Primary + secondary | 550 cc/min | Top feed | LOW IMP | Low impedance years |
| RX-7 FC Turbo II 1988-91 | Primary + secondary | 550 cc/min | Top feed | HIGH IMP | High impedance years |
| RX-7 FD 1993-95 US, 13B-REW | Primary (x2, short rail) | 550 cc/min | Side feed | HIGH IMP | Sprays into center iron |
| RX-7 FD 1993-95 US, 13B-REW | Secondary (x2, long rail) | 850 cc/min | Side feed | HIGH IMP | Common primary upgrade |
| RX-8 2004-11, Renesis | Staged, multiple per rotor | OEM Denso | Top feed | HIGH IMP | Bench data on request |
| Eunos Cosmo 20B (JDM) | Staged, three rotor | OEM Denso | Side feed | HIGH IMP | Import applications |
| Flow figures are the commonly published static ratings at approximately 3 bar (43.5 psi). A popular budget FD upgrade is moving factory 850 cc secondaries into the primary rail; the switchover ratio on the stock ECU is the constraint, so plan the pairing, not just the size. | |||||
Secondaries that idle fine because they never open, then flow 20 percent low at full pulse width. Ultrasonic cleaning usually recovers them fully; the report proves it.
FDs assembled from parts cars end up with mixed year injectors. We identify, flow test, and match a coherent set so tuning is predictable.
FD side feeds use internal rail seals just like the Supra. Hardened o-rings cause leaks and pressure bleed. Every serviced set leaves with fresh seals.
Two 550 cc primary injectors and two 850 cc secondary injectors, all side feed and high impedance. The primaries sit on the short rail and feed the center iron, the secondaries sit on the long rail and feed the outer intake runners.
Within limits. The stock computer reduces primary pulse width to about 39 percent at secondary switchover, so the ratio of primary flow to total flow needs to stay near the factory ratio or the car will stumble lean or rich at staging. That is why the classic stock ECU upgrade keeps the sizing ratio close rather than maximizing each injector.
Oil injection, rich mixtures, and staged secondaries that sit idle for long periods. Fuel varnish bakes onto hot injector tips and the secondaries accumulate deposits precisely because they rarely flow. Regular flow testing is cheap insurance on an engine that does not tolerate lean.
Yes. Side feed Denso injectors are a core part of our service, including ultrasonic cleaning, new seals, filter baskets, and a before and after ASNU flow report showing static flow and spray pattern for each injector.
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