A hypothetical question re: air / fuel mix
Discussion
Ive been thinking lately (all hypothetical):
Say for eg you took the air filter out of your car. Assuming the air was completely clean (so no nasty particles to worry about) this would result in more air in the engine, hence a greater air : fuel ratio in the cylinders, ergo the engine would run lean. Am I right thus far?
So.
These 'performance air filters' alledgedly provide an easy path for air into the engine. Hence, more air in cyls etc etc. Result - lean running - poor performance.
So, when using these aftermarket filters, why dont you have to get yur mixture adjusted?
Say for eg you took the air filter out of your car. Assuming the air was completely clean (so no nasty particles to worry about) this would result in more air in the engine, hence a greater air : fuel ratio in the cylinders, ergo the engine would run lean. Am I right thus far?
So.
These 'performance air filters' alledgedly provide an easy path for air into the engine. Hence, more air in cyls etc etc. Result - lean running - poor performance.
So, when using these aftermarket filters, why dont you have to get yur mixture adjusted?
Depends on your engine.
If you have carbs then the amount of fuel drawn into the cylinde is proportional to the speed of the air flowing through the carb (well approximately) more air means faster flow, means more fuel.
If you have injection theres a thing called a lambda sensor which detects if if the mixture is correct, if its not the ECU will correct the fueling to suit
Simplified description but near enough
In both cases this only works if the change from standardf isnt too big
If you have carbs then the amount of fuel drawn into the cylinde is proportional to the speed of the air flowing through the carb (well approximately) more air means faster flow, means more fuel.
If you have injection theres a thing called a lambda sensor which detects if if the mixture is correct, if its not the ECU will correct the fueling to suit
Simplified description but near enough
In both cases this only works if the change from standardf isnt too big
twin40s said:
Depends on your engine.
If you have carbs then the amount of fuel drawn into the cylinde is proportional to the speed of the air flowing through the carb (well approximately) more air means faster flow, means more fuel.
If you have injection theres a thing called a lambda sensor which detects if if the mixture is correct, if its not the ECU will correct the fueling to suit
Simplified description but near enough
In both cases this only works if the change from standardf isnt too big
So does the ECU learn instantaly? presumably making changes every second, or does it 'take averages' over a few hours / whatever?
SU's and some carbs require new needles...
Injected cars compensate... they have air flow meter, usually either a flap or more commonly a hot wire, from this they 'know' how much air is going in and fuel accordingly, the Lambda sensor is for fine compensation to ensure Lambda 1 (stoichiometric) for maximum cat life and cleaner emissions...
>> to add air flow metering for base control, lambda sensor to close the loop, feedback.
Most injected cars like many carb'd cars before them have various other features to improve transient response, and will still run rich in some situations.
>> daft typo
>> Edited by v8guinness on Thursday 19th February 01:57
>> Edited by v8guinness on Thursday 19th February 02:00
Injected cars compensate... they have air flow meter, usually either a flap or more commonly a hot wire, from this they 'know' how much air is going in and fuel accordingly, the Lambda sensor is for fine compensation to ensure Lambda 1 (stoichiometric) for maximum cat life and cleaner emissions...
>> to add air flow metering for base control, lambda sensor to close the loop, feedback.
Most injected cars like many carb'd cars before them have various other features to improve transient response, and will still run rich in some situations.
>> daft typo
>> Edited by v8guinness on Thursday 19th February 01:57
>> Edited by v8guinness on Thursday 19th February 02:00
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