Fuel System Basics: What Boost Demands From Your Fuel Delivery

The stock fuel system on the 5.7L and 6.4L HEMI is designed for a naturally aspirated engine. It delivers exactly the right amount of fuel for the stock air supply. The moment you add forced induction (supercharger or turbo), the engine is consuming dramatically more air — and it needs proportionally more fuel to match. Without fuel system upgrades, the engine runs lean, detonates, and self-destructs.

The Components

Fuel Injectors

Stock injectors flow approximately 36 lb/hr on the 5.7L and 52 lb/hr on the 6.4L. Under boost, you need 50–80% more fuel flow. Upgraded injectors from DeatschWerks, Injector Dynamics, or Bosch are sized to match your boost level:

• 6–8 PSI boost: 52–62 lb/hr injectors
• 8–12 PSI boost: 72–85 lb/hr injectors
• 12+ PSI boost: 95+ lb/hr injectors

Fuel Pump

The stock fuel pump is the most common failure point in boosted HEMI builds. It simply can't maintain adequate fuel pressure under the increased demand. Options include:

• Fuel pump booster (DeatschWerks DW-FPB) — Increases voltage to the stock pump, boosting flow by 20–30%. Good for mild boost applications.
• Drop-in fuel pump (DeatschWerks DW400, Walbro 450) — Replaces the stock pump with a higher-flow unit. Required for moderate to high boost.
• Dual pump setup (Fore Innovations) — For extreme builds over 800 HP, a return-style fuel system with dual pumps ensures adequate fuel delivery.

Fuel Pressure Regulator

Stock fuel pressure regulators work fine for mild boost but may need upgrading for higher boost levels to maintain consistent fuel rail pressure.

E85/Flex Fuel

E85 ethanol fuel is popular for boosted builds because it's more resistant to detonation, allowing more aggressive timing and boost. However, E85 requires approximately 30% more fuel volume than gasoline, so your injectors and pump need to be sized even larger. A flex fuel kit with an ethanol content sensor lets the ECU automatically adjust for any gas/E85 blend.

The Bottom Line

Never add boost without upgrading fuel delivery. The minimum for any supercharger build is upgraded injectors, a fuel pump upgrade, and a tune. Skimping on the fuel system to save money is the fastest way to a catastrophic engine failure.