https://en.wikipedia.org/wiki/Oxygen_sensor
"Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air–fuel ratio of a combustion engine is rich or lean. "
But still... the 3% better your exhaust flows now is completely starving that engine of fuel because the exhaust gasses are just rocketing out of the engine so fast the fuel system cant keep up. Its not defaulting to super rich by design or anything because there is no O2 sensor hooked up. Does it puff black smoke when you mash on it? I know that helps power big time with diesel engines, its just weird how trucks with tbi blowing black smoke lose power?
If your serious about that last sentence.... It doesn't "help" power in diesels when blowing black smoke, just in some cases its a bi product of higher power not burning the fuel effeciently. Black smoke is unburned fuel, gas or diesel.
Is a diesel, black smoke does not at all mean the engine has more power, it just means the engine has more fuel than it needs, that for some reason or purposefully, there is fuel that cannot be burned due to a lack of air needed to burn a certain volume of fuel. Essentialy, not really robbing it of power.
In a gas engine, the same basic idea is here too...Just overfueling hurts the engine powerwise.
This is because your putting more fuel in, but with the lack of air for that fuel the combustion will not have the power of one that has the correct air fuel ratio, 14.7:1
I'd assume the reason for difference is due to either or both the fuel combustibility differences, and the combustion process differences
