Power Duct or "power-loss" Duct - Someone please explain to me
Power Duct or "power-loss" Duct - Someone please explain to me
So I moved away from the z-tube and jwt pop charger and back to the stock setup. The car has gotten quieter and my mpgs have gone up slightly maybe because I am no longer instinctively driving aggressively due to the lack of the growling tone that excited my auditory senses.
I was looking at the stock air box and power duct and it dawned upon me...using the information from my fluid dynamics class some 9 years ago, I would not have made a large gapping hole in the middle of a intake expecting MORE airflow into the engine, especially because the hood closely quite tightly against the power duct.
If the power duct was closed, and the vehicle moving at a high speed, air is being pushed through the intake and into the engine. As the speed increases, air would be forced in at a faster rate thus producing more power, at this point the power duct would be nothing more than a place for excess air to come out rather than being forced into the engine....hmmm interesting...hence my notion for power-loss. I would compare this very loosely to say a blower that had a open hole in the piping.
To test my theory, I duct taped the power duct and drove around....now I could not tell any noticeable difference, maybe a a little more growl to it.
While the vehicle was idling, i poked a 1/2" hole in the duct tape that was covering the power duct...my air flow measuring device was a simple long neck lighter and flame. At idle no air was drawn into the 1/2" hole, but there was slight air flow into the stock intake. Upon revving the engine to 4500rpm, enough air was sucked in that the flame shot into the 1/2" hole and extinguished immediately , the same was true at the stock air intake duct. So the vehicle was indeed hungry for air.
This was at a stand still with no air flowing. I'd imagine that while moving at higher speeds, sufficient or even excess air is provided though the stock duct that the engine does not starve, but rather an excess of air is available, which is then released out though the power duct rather than into the engine.
So unless I should have indeed failed my fluid dynamics class, can some explain to me the working of the power duct given that once the hood is closed less than an inch of area is available for air flow through the power duct. The Infiniti manuals and service manuals provide no explanations.
Perhaps there is a way to measure air flow or air flow direction at the power duct based off of an OBD-II reading from the MAF sensor or even a home-made device?
One would think that the resonator under the power duct box if cut open with a hole facing the front would form a nice scoop for air to be sucked in. Maybe that should be my next experiment.
I was looking at the stock air box and power duct and it dawned upon me...using the information from my fluid dynamics class some 9 years ago, I would not have made a large gapping hole in the middle of a intake expecting MORE airflow into the engine, especially because the hood closely quite tightly against the power duct.
If the power duct was closed, and the vehicle moving at a high speed, air is being pushed through the intake and into the engine. As the speed increases, air would be forced in at a faster rate thus producing more power, at this point the power duct would be nothing more than a place for excess air to come out rather than being forced into the engine....hmmm interesting...hence my notion for power-loss. I would compare this very loosely to say a blower that had a open hole in the piping.
To test my theory, I duct taped the power duct and drove around....now I could not tell any noticeable difference, maybe a a little more growl to it.
While the vehicle was idling, i poked a 1/2" hole in the duct tape that was covering the power duct...my air flow measuring device was a simple long neck lighter and flame. At idle no air was drawn into the 1/2" hole, but there was slight air flow into the stock intake. Upon revving the engine to 4500rpm, enough air was sucked in that the flame shot into the 1/2" hole and extinguished immediately , the same was true at the stock air intake duct. So the vehicle was indeed hungry for air.
This was at a stand still with no air flowing. I'd imagine that while moving at higher speeds, sufficient or even excess air is provided though the stock duct that the engine does not starve, but rather an excess of air is available, which is then released out though the power duct rather than into the engine.
So unless I should have indeed failed my fluid dynamics class, can some explain to me the working of the power duct given that once the hood is closed less than an inch of area is available for air flow through the power duct. The Infiniti manuals and service manuals provide no explanations.
Perhaps there is a way to measure air flow or air flow direction at the power duct based off of an OBD-II reading from the MAF sensor or even a home-made device?
One would think that the resonator under the power duct box if cut open with a hole facing the front would form a nice scoop for air to be sucked in. Maybe that should be my next experiment.
Last edited by d_pak; Apr 28, 2008 at 03:00 PM.
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Originally Posted by d_pak
So unless I should have indeed failed my fluid dynamics class, can some explain to me the working of the power duct given that once the hood is closed less than an inch of area is available for air flow through the power duct.
Just remember that the area in front of the radiator is pressurized while the car is moving forward. All the duct does is give a little more volume for the airflow. This spoken by someone who didn't take a fluid dynamics class, so I could be completly wrong...but I'm not.
I'm a chemical engineer working on PhD, maybe I can help you out here. the reason the power duct works is that at speed, the inlet into the engine is essentially a vacuum. Both the snorkel and the power duct will be at higher pressures relative to the intake tube so the air will flow into the engine to try to equalize the pressure. Essentially what the power duct is doing is increasing the area the the air can flow back into the air box decreasing the pressure drop across the air box. If the inlet into the box is too small then the pressure drop across the inlet would result in a restricted flowrate which could make the inlet into the intake box the limiting portion of the intake system as opposed to the intake tube.
Last edited by redlude97; Apr 30, 2008 at 03:49 AM.
