zhangmessiok

When you accelerate the engine makes a sound, but when you use the engine-brake, is another sound. What determines this sound?

Way too complicated a matter to discuss in accurate & complete detail here.

Accel and Deccel are 2 entirely different modes,,practically "alternate universes"

In Accel,,,the Intake Velocity is very High and Voluminous.
Combustion Chamber Pressures are High ,,and Rising by the RPM.
Exhaust is Pressurized to the point it constitutes a Flow Restriction,,,,Likewise on Intake Side'sVaccum being restricted by mass volume demand.
Intake Gulp Frequency is communicated all the way thru to altmosphere

On DECCEL,,Air Intake is almost NIL,,,,
Carb & Downstream Intake tract is under Extreme High Vacuum while Carb Intake is under a near NO Flow/Atmospheric Pressure condition.
It's virtually Isolated from atmosphere

Combustion is almost NIL,,hence Pressure is limited to engine's physical displacement.
And even THAT is being starved by Closed Throttle.
Engine is pumping "NO Air" to compress,,,None to support combustion.

PSI entering Exhaust falls thru the floor.

What WAS The "Restrictive " Exhaust under ACCELERATION,,,
instantly becomes Relatively CAVERNOUS compared to the Mass of Air it must pass under Deccel.
Or I should say LACK of Air

The Reduced AirFlow Mass,,,Drops the Velocity at exhaust outlet.
With practically NO Back Pressure on exhaust,,,the "Pop" of the engine's pumping is communicated thru the exhaust with additional resonance due to the rapid Rise/Fall of system pressures.

Not reffering to lean misfire pop,,,but the popgun/bottle cork rarefaction type of "pop"

Lots more complicated and complex than that,,,
but it all boils down to the effects of Air Mass,and Pressure,and Velocities at different point of the engine /Air Intake/Exhaust.

All of which behave entirely differently during accel/deccel

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