Air Fuel
Ratios
Gasoline = 14.7:1 (This is
stoichiometric or 'scientifically' correct providing enough oxygen to burn
all the fuel)
Gasoline = 14.3:1 (This is
stoichiometric for gasoline with 10% ethanol)
Gasoline -
Naturally aspirated best power = 12.5:1 to 13.2:1 (This depends
on the engine, and all the factors that affect stratification and burn
efficiency - In general you give the engine what it wants)
Gasoline -
turbo = 11.8:1 to 12.5:1 (This depends on the engine. The
extra fuel absorbs the added intake heat and the vaporization of it cools
the intake charge and the richer mixture provides a level of safety)
Gasoline -
turbo, old school non intercooled and roots supercharged = 11.0:1 to
11.9:1 (This depends on the engine. You're flooding a fire hose of
fuel down the intake here. The extra fuel absorbs the added intake heat and
the vaporization of it cools the intake charge. It can also help if
the carb or a fuel injector is pre roots blower to lube and seal seal the
rotor strips.)
E85 Gasoline
- 9.7:1 to 9.8:1
(This is stoichiometric or
'scientifically' correct providing enough oxygen to burn all the fuel)
E85 Gasoline
- Naturally aspirated best power =7.0:1 to 8.5:1 (This depends on the
engine, and all the factors that affect stratification and burn efficiency
- In general you give the engine what it wants)
Ethanol -
9.0:1
(This is stoichiometric or
'scientifically' correct providing enough oxygen to burn all the fuel)
Ethanol -
Naturally aspirated best power = 6.4 to 7.8 (This depends on the engine,
and all the factors that affect stratification and burn efficiency -
In general you give the engine what it wants) Note that Ethanol can yield a
4 to 5% power gain as it cools the intake charge better than gasoline due to
latent heat of vaporization.
Methanol -
6.5:1
(This is stoichiometric or
'scientifically' correct providing enough oxygen to burn all the fuel.
You can idle on this but running and best power are richer still.)
Methanol -
4.5:1 to 5.5:1 (This depends on the engine. It's very rich but
supercharged engines will eat this mixture right up - Like gasoline,
you give the engine what it wants. Also, commercial Air Fuel Meters
often respond much too slowly to the signal when Methanol goes lean, so you
will often hear that "the readings were good" but the racer lost a piston.
Start too rich and tune so the burble goes away.) Note that Methanol can
yield a 10 to 20% power gain and while it lights off easy -think glow plug
in RC car and plane engines - its richness and latent heat of evaporation
allow it to wick the heat from hot spots in the combustion chamber allowing
high compression ratios or higher boost levels without detonation.
Nitromethane-
2.5:1 to as much as 1.0:1 under load! (Nitro (CH3NO2)
is nearly a mono propellant. That means it requires almost no
additional oxygen from the atmosphere to burn. Ounce for ounce it
contains about half the heat energy of gasoline. Since it requires
around 5 times as much fuel as gasoline to run, it can double an engines
power output. It also does not tune like gasoline at all. Throw
out everything you know when it comes to tuning an engine.)
Note - When
using a commercial AFR meter: Oxygen sensors measure excess air.
They read and think in Lamda - 1.00 is stoichiometric. A commercial
meter will generate a reading of 14.7 when running at stoichiometric on
gasoline or Ethanol or Methanol.
Lambda
= actual AFR / stoich AFR
For Gasoline:
14.7:1 = 1.00 Lamda
12.5:1 = 0.85 Lamda
For Ethanol
9.0:1 = 1.00 Lambda
7.6:1 = 0.85 Lambda
For Methanol
6.5:1 = 1.00 Lambda
5.5:1 = 0.85 Lambda
Your gasoline AFR meter should be read and be tuned like a gasoline AFR
meter when running other fuels. It doesn't know you are running a
different fuel, all it sees and measures is excess oxygen and converts
Lambda to the gasoline AFR scale for display purposes.
Professional grade units can be switched to read either straight Lamda,
Gasoline AFR, Ethanol AFR or Methanol AFR.
In
our case, our units can be configured for Gasoline, Ethanol, Methanol,
Diesel, Propane, CNG or custom blends (such as E10 @ 14.2:1).
