Fuel System Sizing
Pick a power target, pick a fuel — get the fuel flow, injector size, pump capacity and feed line the job actually needs. The comparison table shows why E85 and methanol change everything.
Fuel flow
209 L/h
Mass flow
164 kg/h
Per injector
871 cc/min
Injector to buy @ 80%
1,088 cc/min
Pump @ +25% headroom
261 L/h
Feed line rule of thumb
AN-8 (≈11 mm ID)
Sizing the pump: quote its flow AT your rail pressure (a “255 L/h” pump is usually rated at 3 bar — it flows far less at 4–6 bar, and even less on 12 V vs 13.5 V). Return/bypass line: one size down.
Same power, different fuel — why E85 needs bigger everything
| Fuel | Volume flow | Total injector | Per injector @ 80% | Pump @ +25% | Feed line |
|---|---|---|---|---|---|
| Petrol | 146.1 L/h | 2,435 cc/min | 761 cc/min | 183 L/h | AN-6 (≈8 mm ID) |
| E10 | 152 L/h | 2,534 cc/min | 792 cc/min | 190 L/h | AN-8 (≈11 mm ID) |
| E85 ← | 209 L/h | 3,483 cc/min | 1,088 cc/min | 261 L/h | AN-8 (≈11 mm ID) |
| Methanol | 303.9 L/h | 5,065 cc/min | 1,583 cc/min | 380 L/h | AN-10 (≈14 mm ID) |
E85 ~30–40% and methanol >2× the volume of petrol for the same energy — budget for the whole fuel system (tank, lines, filter, rail), not just injectors. Methanol is also corrosive to bare aluminium and some elastomers.
Good to know
- BSFC assumptions: 0.50 lb/hp·hr naturally aspirated, 0.60 boosted, petrol-equivalent energy. Rich-lambda race tunes sit at the higher end.
- Injector sizing lists the cc/min rating you should BUY at your chosen duty cycle — buying at 80% duty leaves headroom for hot days and boost spikes.
- Pump flow must be quoted at your rail pressure: a “300 L/h” pump usually drops to 200-odd at 5 bar, and lower still on a tired 12 V supply.
- Line sizes are a velocity rule of thumb, not a pressure-drop study — long runs, E85 and methanol pumps all justify stepping one size up.