What size injectors do I need for E85?

For E85, size the injectors for about 45% more fuel (by weight) than the same engine needs on gasoline (that is the ratio of the sizing values below, 0.80 vs 0.55). The math we use (the same as our fuel and E85 guide and fuel system calculator):

Last updated October 13, 2026

Injector flow (lb/hr) = horsepower × BSFC ÷ number of cylinders ÷ 0.80

• BSFC is how much fuel the engine burns per horsepower per hour. For sizing we use 0.80 for E85 and 0.55 for gasoline (conservative values, so you end up with headroom).
• ÷ 0.80 keeps the injector at 80% duty cycle at peak power, so it isn't wide open with nothing left.
• The answer is the flow you need at the fuel pressure you actually run. Injectors are usually rated at 43.5 psi (3 bar); a factory LS returnless system runs about 58 psi, where the same injector flows about 15.5% more (√(58 ÷ 43.5) ≈ 1.155).

Worked example: a 450 hp naturally aspirated LS on E85.

1. 450 × 0.80 = 360 lb/hr of fuel for the whole engine.
2. 360 ÷ 8 cylinders = 45 lb/hr per injector.
3. 45 ÷ 0.80 = 56.2 lb/hr per injector at your running pressure.
4. On a 58 psi returnless system, divide by 1.155: look for injectors rated about 48.7 lb/hr at 43.5 psi. The same engine on gasoline needs about 33.5 lb/hr rated, which is why stock injectors run out on E85 long before they do on gasoline.

Quick sizing for a naturally aspirated V8 (lb/hr per injector, BSFC 0.55 gasoline / 0.80 E85, 80% duty):

Engine power	Gasoline, at running pressure	Gasoline, rated at 43.5 psi (run at 58)	E85, at running pressure	E85, rated at 43.5 psi (run at 58)
350 hp	30	26	44	38
400 hp	34	30	50	43
450 hp	39	33	56	49
500 hp	43	37	62	54
550 hp	47	41	69	60
600 hp	52	45	75	65
700 hp	60	52	88	76
800 hp	69	60	100	87

Pick the next size up, not the closest one: a bigger injector costs nothing in power, a small one runs out of fuel at the top.

Flex fuel: size for E85. The injector has to cover the worst case, and that's a full tank of E85.

Boost: the table is for naturally aspirated engines. A boosted engine can burn more fuel per horsepower than these values assume, so the table may undersize injectors for boost: size them with a higher, boosted BSFC in the same formula and leave extra margin, or have your tuner size them for your boost level. The pressure part still works the same way with a 1:1 boost-referenced regulator, because the pressure across the injector stays at the base pressure; on a returnless system that isn't boost-referenced, the pressure across the injector drops as boost rises, so you need more injector again. The power number in the formula is engine power, not wheel power.

After you install them: the tune needs the new injector's flow data and offsets (short pulse and voltage correction), not just a bigger number: what injector data to enter. Then log injector duty cycle at wide-open throttle and keep it under about 80%.

The pump has to keep up too: the 45% is fuel by weight. E85 is a little denser than gasoline, so by volume (what pump ratings are in) the same sizing values work out to about 34% more flow than gasoline for the same power, before you add margin, and pump flow also depends on the pressure it runs at. Our fuel guide walks through pump sizing.