Quote:
Originally Posted by XutvJet
No one has really touched on the fact of why BMW placed the OEM scoops like they do:
1) Keeps dirt and sandy debris from flying directly into the intake. Not a huge deal considering the car is running a filter. It simply means the filter might clog up a bit faster.
2) Most importantly, the air slamming into radiator at speed creates pressure on the frontal face of the radiator, thus the air pushes itself into the intake scoop placed directly in this area and as the intake is sucking in air, this pressurized air will take the path of least resistance and head for the scoop. This improves throttle response (maybe power but only VERY marginally).
By placing the scoop forward facing, you lose the pressurization effect. It can also create turbulence along the leading edges of the scoop, thus somewhat lessening the ability of the air to shove itself into the intake and ultimately taking away some throttle response as well.
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So... to be transparent... I am not an engineer, just a crazed car nut. Further, I do not, and would not go against BMW engineering. I am very confident the stock M3/M4 side airbox inlets work well, and pretty much exactly as you described.
They rely on this pressurization effect the same way the radiators / heat exchangers do.
However, while there maybe some edge turbulence (although none was seen on the simulation software) I do struggle to see how a 90 degree right turn (stock M3 / M4 inlet nozzle) will have better airflow than what I'm presenting here, which has a much more direct path for intake air. Simulation software also suggested that the shape (velocity stack) does accelerate the incoming air a little bit.
I agree the intake pressure
might be lower because of this loss of pressurization effect, but then again the forward facing inlet should build pressure as the car moves through the air. If we agree that flow is proportional to the pressure gradient... Then whichever design increases the proximal pressure the most would create the best flow... But this assumes the shape of the inlets are the same, which is where I worry about the sharp angle of the stock M3/M4 inlet.
Another factor to consider is the the secondary hot air port in the OEM piece from the filter to the inlet nozzle. This port would likely lose a lot of the pressure built up on the inlet before it reached the filter... Again it's all speculative physics.
I certainly have no basis to say this design is superior to the OEM M3/M4 but... I do not expect it to be inferior (hope it isn't!). While running the prototypes I have noticed improved throttle response in the 4k range. But I will test everything and then we can see the numbers.