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Fuel, E85 & boost tuning

More power means more fuel, and the tune has to know exactly what's feeding the engine.

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Fuel system first

• Size the injectors and pump for your power and fuel with the fuel system calculator, then enter the injector data in the tune.
• Stock limits: Stock LS fuel filter/regulator assembly tops out around 450 hp; beyond that, larger lines and an external regulator.
• Pressure and lines: LS EFI needs about 58 psi vs 5–7 psi for a carbureted small block; parts-store hose clamps/rubber hose are not adequate at 60 psi. Use AN hardlines, push-on hose/fittings, or ethanol-safe hose (e.g., Earl's Vapor Guard).
• More in the fuel, E85 & injector guide.

E85

E85 needs substantially more fuel than gasoline for the same power (size injectors and pump for it). On boosted engines, Speedway notes E85 lets you safely run more boost and timing than pump gas; water/methanol injection is an alternative where E85 isn't available.

Boost

• There's no single safe boost number: air/fuel ratio, timing advance and boost pressure have to be balanced across the rpm range. Speedway recommends an experienced calibrator or dyno tuner.
• How well you cool the intake charge limits how much boost you can run.
• Turbo size matters: too small and more boost won't add power; too big and it lags and struggles to reach peak boost.
• Stock LS bottom ends have survived very high power, but tune quality decides whether they live.
• On a stock-bottom-end 4.8, Speedway recommends no more than 8 psi.

What the sources say

Paraphrased from the linked sources (29 points). Specifics depend on your computer and operating system.

Show all

• Terminator X, HP, Dominator; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Aeromotive's bypass regulator provides a vacuum/boost reference port for fuel pressure compensation at a 1:1 rate, a feature aimed primarily at blow-through centrifugal supercharger applications. Aeromotive
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: AEM's universal adjustable regulator has a 1:1 vacuum reference, meaning each pound of boost adds one pound of fuel pressure, and its adjustment range runs from 20 psi up to whatever the fuel pump can deliver. AEM
• E38, P59; LQ4, LQ9, LM7; 1999-2007: ZZ Performance's boost-referenced fuel pressure kit for return-style GM systems lowers rail pressure to 38-42 psi at idle under full vacuum and rises 1:1 under boost, but the change requires PCM programming to match. ZZ Performance
• E38, E67, Terminator X, Dominator; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: The flex fuel sensor is designed for installation in the fuel return line; its straight-through 3/8-inch (9.5 mm) tube adds minimal restriction, which suits high-horsepower fuel systems, and it resists the corrosive properties of high-ethanol blends. Syvecs
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: In observed real-world consumption, pure E85 raises fuel use by roughly 25-30% over gasoline (E50 only about 5-10%), and pump-labeled E85 can legally contain anywhere from 51% to 83% ethanol. eFlexFuel
  Sources differ: Conflicts with the 52% stoichiometric figure; the manual's observed consumption increase is smaller than the stoich-ratio math implies.
• P01, P59; LM7, LQ4, LQ9, LS1, LS2; 1999-2007: HP Tuners' 2-bar/3-bar MAP support (the 2.5-bar custom OS) adds a Boost VE table spanning 105 kPa to 255 kPa with better than 5 kPa resolution in the boost region, retains stock VE resolution in non-boost areas, adds a MAP-referenced Boost Enrich table in 5 kPa steps, and runs in speed-density mode only. HP Tuners
  Sources differ: Conflicts with simpler '2-bar good to 14.7 psi' statements; the OS boost tables actually read to 255 kPa when paired with a 3-bar sensor.
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: A boost-referenced fuel pressure regulator uses a vacuum/boost port with a 1:1 ratio: every pound of manifold pressure raises rail pressure by one psi, so injector differential pressure stays constant. For example, 10 psi of boost on a 45 psi base takes the rail to 55 psi. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Without a boost-referenced regulator, manifold pressure pushes back on the discharge side of the injector and reduces effective fuel delivery. On a 45 psi system with 10 psi of boost, the injector only discharges at 35 psi, making the engine run lean; 40 psi of boost would leave just 5 psi of discharge pressure. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: A boost-referenced regulator also compensates in reverse under engine vacuum: it lowers rail pressure proportionally so that intake vacuum does not pull extra fuel through the injector, keeping the differential ratio consistent at all times. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: The net result of a properly boost-referenced fuel pressure regulator is a constant injector flow rate regardless of intake manifold pressure. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Fuel injectors are rated at a specific differential fuel pressure, most commonly 43.5 psi (3 bar) and 58 psi (4 bar); effective flow rate at any other pressure scales with the square root of the pressure differential. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: When sizing injectors, confirm the selected flow rate at the fuel pressure the system will actually run, and account for a boost-referenced regulator raising base pressure proportionally with boost. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: The industry-standard maximum operating duty cycle for port fuel injectors in continuous high-performance use is 80%; at 100% the injector becomes an uncontrolled open orifice and the ECU loses fine fuel control. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Injector minimum flow per cylinder is computed as (Gross Design Power x BSFC / cylinders) / 0.80, which enforces the 80% duty cycle ceiling directly in the sizing math. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Fuel systems on forced-induction builds must be sized for gross power including the supercharger's parasitic draw; a ProCharger F1-X consumes roughly 160-200 HP at full boost, so a 1,200 BHP target needs injectors sized for 1,360-1,400 BHP of fuel demand. LSX Magazine
• E38, E67, P59; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Advanced Fuel Dynamics' E85 system uses the GM-style inline sensor to monitor ethanol content and automatically steps injector output up as ethanol rises; the sensor re-reads content every 1/10 of a second, so blends adjust on the fly without a retune. Pump E85 can range from 51% to 83% ethanol. MotorTrend
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: E85 has a blended stoichiometric air/fuel ratio of approximately 9.7:1 to 9.8:1 versus about 14.7:1 for gasoline; ethanol's much lower energy density by mass is what forces considerably higher fuel mass flow for the same power. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: By brake-specific fuel consumption, E85 (BSFC 0.80 lb/hp-hr) demands roughly 45% more fuel mass than gasoline (BSFC 0.55) to make the same power. LSX Magazine
  Sources differ: Conflicts with sources claiming ~30% more fuel (Holley forum, AFD/MotorTrend) and with the 52% stoichiometric-ratio figure (Holley forum, 14.7/9.65=1.52).
• P01, P59; LS1; 1998-2002: Converting a fourth-gen F-body LS1 to E85 required swapping to high-flow E85-compatible fuel pumps and larger injectors, because ethanol's substantially lower lubricity quickly wears out a standard pump not designed for it; OBD-II-era fuel systems otherwise already tolerate the ~10% ethanol in pump gas. LSX Magazine
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: A proper E85 fuel system needs 30-40% more flow capacity than the gasoline equivalent; injectors should be sized to stay at or below 90% duty cycle and the pump should carry 10-20% headroom. Materials to avoid include PVC, nitrile, natural rubber, urethane, non-anodized aluminum, zinc, brass, and untreated ferrous metals, and pre-2001 OE fuel systems were not engineered for any ethanol concentration. Performance Racing Industry
• E38, E67, P01, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: For E85 service, injectors with stainless steel internals (such as Bosch EV14) resist the corrosive environment, Viton O-rings are the preferred seal material, and a serviceable inlet filter on each injector serves as the last line of defense against fuel-system residue clogging. Performance Racing Industry
• LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: On an E85 carbureted setup, Quick Fuel recommends an AN-10 line from tank to regulator and AN-8 from regulator to carb, all braided stainless or hardline with no rubber, a pump capable of 250 gph, carb fuel pressure at 6 to 6.5 psi, and steel-micron filters instead of paper. MotorTrend
• E38, E67, P01, P59; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: As boost rises, the ignition curve benefits from a small retard function because the denser, more turbulent boosted mixture burns faster; this same concept also permits keeping more advance at low-speed cruise while pulling advance back at high boost. Corky Bell / Maximum Boost
• E38, E67, P01, P59; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: A boost-pressure-actuated ignition retard is a compromise: it progressively retards timing as boost climbs even when no detonation is present, so mid-range timing ends up sub-optimal in order to be correct at maximum boost, costing noticeable mid-range torque. Corky Bell / Maximum Boost
• E38, E67, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: A flex fuel sensor sits inline in the fuel line before the fuel rail and measures the ethanol-to-gasoline ratio so the ECM can adjust ignition timing and injected fuel quantity for the actual blend in the tank. CPR Racing
• E38, E67, P59, Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: The GM/Continental flex fuel sensor uses a three-wire connector: ground, battery-positive power, and a signal wire carrying ethanol percentage as a frequency signal. The ECM supplies an internal 5V pull-up on the signal circuit, which the sensor pulses to ground; normal operation is 50-150 Hz, while 180-190 Hz flags contaminated fuel. CPR Racing
• Terminator X, HP, Dominator; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Aftermarket plug-and-play flex fuel harnesses for Holley EFI insert into the 4-pin power tap on the main harness; the signal lead pins into an open frequency-type input, and the required pull-up resistor comes pre-wired. These harnesses fit Terminator X, HP, and Dominator systems with GM/Continental sensors. Jolt Systems
• Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Terminator X ECUs expose four input types (12V, ground, 5V, and frequency); the frequency input is the one used to read a flex fuel sensor. Texas Speed
• Terminator X; LM7, LQ4, LQ9, LS1, LS3, LS6; 1999-2013: Terminator X ECUs carry an onboard 1-bar MAP sensor suited to naturally aspirated or nitrous combinations; for boosted applications the internal sensor is disabled and an external sensor is used, with Holley recommending GM part 12592525 plus adapter 558-416 for 2-bar and up. Texas Speed

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