Lean burn
Introduction
Lean burn systems are designed into several cars, particularly the Honda Civic. Cars that do not have lean burn systems can be modified to run in a lean burn state.
Any carbureted vehicle can be tuned for lean burn with the use of that carburetors tuning kit a wide band oxygen sensing meter.
The benefit of lean burn is that because more air is being used by the engine the throttle opens more which reduces the vacuum generated and therefore reduces the energy used to produce the vacuum. The other benefit is that more of the fuel is burnt when excess air is present in the combustion chamber
Small piston driven air craft also run adjust on the fly carburetors that allow for lean burn while at cruise altitude and speed. Pilots claim a fuel economy improvement of around 20% with lean burn.
Note: Lean burn cars typically have special type of catalytic converter which reduce NOx even when non stoichiometric fuel ratios are used.
Contents
Instructions for mod
For Carbureted vehicle: Install a wide band oxygen sensor meter first and drive around establishing a MPG base if you don't already have one and make note of air fuel ratios and typical driving conditions.
If you attempt to run a lean burn tune with out a wide band oxygen sensing meter engine damage could result, mainly burned exhaust valves.
Then once you have your base line established start tuning from there. Fuel metering rate can sometimes be adjusted with a metering screw, but usually requires swapping out metering rods or metering jets.
Tune the carburetor to idle around 16:1 to 17:1 air fuel ratio. Then while driving down the road tune for around 15:1 to 17:1 with a target of 16:1 for cruising at speed. While accelerating try to tune for 14:1 air fuel ratio plus or minus 1. The closer to 14:1 the better. Then for wide open throttle tune air fuel for as close to 13:1 air fuel ratio as possible.
As far as how to lean burn a fuel injection system goes each type of engine control system has its own specific way.
All most all OBDI and early OBD2 vehicles are designed to specifically to avoid ever running in any lean burn condition.
User experiences
Please enter your user name and any relevant data in the table
| User Name | Car Make, Model, Year | Cost of Mod | Time to Perform Mod | MPG Before Mod | MPG After Mod | MPG improvement guess | Instruction Link |
|---|---|---|---|---|---|---|---|
| Oil Pan 4 | 1984 Chevy suburban 454 | $300 USD | 8 Hour | 6.55mpg | 10.1mpg | 54% | [Lean burn 7.4L|Wide band oxygen meter] |
Problems / Consequences of mod
If you run lean burn when trying to accelerate or at wide open throttle you can burn exhaust valves and cause engine misfire.
References
Prerequisite mods
Forum thread links
AutoSpeed on running lean for fuel economy
Converting Cali Civic VX to Fed (lean burn) VX
How does Lean-burn actually save fuel
Lean burn on my 454 suburban (6.5mpg running rich then tuned to lean burn seeing a 4mpg improvement)
External links
Autospeed, great info on O2 sensors, open/closed loop and adjusting air fuel ratio
