λ · Race gas & E85 blend calculator
Blend race gas & E85 with the math done right.
Mass-weighted AFR and molar octane — not the linear average forum spreadsheets get wrong. Free, no signup.
When the math has to be right
Close enough isn’t a tune. It’s a gamble.
- You blended to "95 AKI" off a spreadsheet — but it averaged octane in a straight line (it doesn't work that way).
- You splashed E85 and guessed the ethanol % instead of calculating it.
- Pump E85 is really E70–E83 — so your ‘85’ math was off from the start.
- You're sizing injectors off a sticker, not your actual fuel and target power.
- One wrong AFR call and it's a piston — not a redo.
The chemistry, not the shortcut
The number you tune to is the number in the tank.
Every result is mass-weighted AFR + molar octane — the way fuel actually mixes. Open the breakdown and check it yourself.
Race-gas blend
Mix 110/116 + pump → true resulting AKI, AFR & density.
E85 flex blend
E85 + 91/93 → your exact ethanol % and target AFR.
Injector sizing
Real lb/hr for your fuel and power target.
What you get
- Tune to a number you can trust — not a forum average.
- Hit target octane without overspending on race gas.
- Nail ethanol % on a splash blend, every time.
- Size injectors once, right — no second-guessing.
- Works in the shop, on your phone, in seconds.
- Free — no account, no paywall to get the answer.
Pricing
Free to calculate. Pro to keep.
Free
$0 forever
Every calculator, no account.
- Race-gas & E85 blend
- Target AFR & octane
- Injector sizing
Pro
$29/yr
Everything in Free, plus:
- ✓ Saved blends + cloud sync
- ✓ Race-fuel library
- ✓ Injector duty-cycle (IDC) validation
- ✓ PDF export
Billing via Paddle (Merchant of Record, USD). Prices as of June 2026.
The proof is the math
No fake reviews. Open formulas.
New tool, no recycled testimonials. The credibility is the engine: the same validated core behind Lambda, with auditable formulas — mass-weighted AFR, molar octane, real density. Run it, open the breakdown, verify before you trust it.
AFR
mass-weighted
Octane
molar
Injectors
lb/hr
Straight answers
Free? What’s the catch.
None — the calculator is free, forever. Pro ($29/yr or $49 lifetime) adds saved blends, cloud sync, the race-fuel library, IDC validation and PDF export.
My spreadsheet already does this.
It averages linearly. Octane and AFR don’t. That’s the whole point.
Another generic calculator?
Open the breakdown: mass-weighted AFR, molar octane, real density. Generic calcs can’t show their math — because it’s wrong.
Is it accurate?
Same validated core as Lambda, with public/auditable formulas. It’s a planning tool — you make the final call.
FAQ
Do I need an account?
No. Open it, calculate, done.
What fuels does it cover?
Pump 87–93 AKI, race gas (100–116), E85/flex, methanol blends.
Does it size injectors?
Yes — lb/hr for your fuel and target power.
Is pump E85 really 85%?
Usually E70–E83. Lambda lets you calc the real %.
Will it stay free?
The calculator is free, forever — no account needed. Pro ($29/yr or $49 lifetime) adds saved blends, cloud sync, the race-fuel library, IDC validation and PDF export.
Blend on the math,
not a forum average.
The number in your tank should be the number you tuned to.
Calculate my blend — freeP.S. — Forum spreadsheets average octane in a straight line. Engines don’t. Lambda does the real chemistry, free, in your pocket — so the next blend is dialed, not guessed.
Off-road / race use. Lambda is a planning tool — the final tuning decision is yours.