Quote:
Originally Posted by YarkoDrives
Just unpacked the BMW Performance Intake Parts.
The "third intake" looks to be an outlet to maintain airflow thru the box at speed, even when the throttle is closed.
the channel is the full width of the cover about 1/2" deep it starts halfway down the cover. It runs along the back half of the air box toward the strut tower. A sealed plastic cap completes the tunnels along the outer side of the strut tower. It terminates at 2 small holes each about the size of a nickel behind the strut tower, at the cowl weatherstrip.
I can't image these two small holes are serving any function as an intake. Though perhaps they may whistle is the throttle is pressed quickly, when the car is parked, as there would be no airflow thru the box due to forward movement.
At speed the cowl is a low pressure area, the low pressure will pull air through the air box. this is a good thing:
So image the throttle is closed going into a corner, the car is moving fast enough to create negative pressure on the cowl, so thru the tiny ports air is being sucked through the airbox. Cool Air is moving from the scoops thru the inlets, and over the air filter...
Now, coming out of the corner the throttle opens and takes cold air from the stream over the filter. So, effectively the intake length is shorter.
Consider the stock box:
assuming there's no similar pull-thru outlet on a stock box, once the throttle closes the air in the airbox is stale, just a little comes thru for idle. The air also absorbs some heat while stagnate. At speed when the throttle opens the closest cool air is at the scoops at the front of the car. It has to get all warm air in the box and inlet moving before that air is available.
There's also some fluid dynamics to having a side stream of air; it allows the additional air needed for the opening throttle slide along with the existing stream without creating turbulence. in the front of the intake.
In the stock system quickly opening the throttle creates turbulence in the inlets; that results in a less efficient delivery and a sucking sound.
All that said, I agree with the popular opinion the Performance intake is 90% Sexy and 10% performance.
If the Assist-flow stream, better throttle response is there it would only be tested at speed. Maybe log throttle position/request vs MAF/ throttle fuel delivery to see if there is less time between the two with the performance intake vs the stock.
Anyone got a wind-tunnell dyno to use we could find out if it's 3hp or 0.03hp gained.
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Or it could be to direct a little intake noise towards the cabin to enhance its "sporty" nature.