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Old 10-03-2013, 03:54 PM   #13
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Join Date: Feb 2003
Chapter/Region: SCIC
Location: Woodland Hills
2007 2.34LR, EFR7670
LINK G4+ hybrid STi


Originally Posted by Mr Wrex View Post
If you're not going to use a turbo with a 3" opening, don't use the larger inlet. Think about it like this... vaccuum attachments cover different amounts of surface area. The larger the surface area where the air initially enters the "system", the slower the air will move. As the area for the air to move through becomes smaller, the air will start to move into the "system" faster. If, for example, we use a vaccuum attachment that has the same inner diameter as the rest of the piping leading to the "system", the air's speed will stay the same speed at all times. Overall, it doesn't matter which size attachment you use... the air will still flow through the "system" at the same rate since you aren't changing the diameter of the piping all the way to the engine.

Another example... go suck air through a straw. Then after, attack a cone with a larger opening to the end of the straw and try sucking air in again. Notice a difference? (you shouldn't)

In summary, you will only flow as fast as your smallest part will allow you to. I don't even have to discuss the possible downfalls of the adapter/reducer to prove that this is no bueno.
That's not true. The flow losses from point A to point B are cumlative. Your example used the same length of straw of the same diameter then you added a cone at the end. Instead make a new straw the same length as the old one but instead of a constant diameter, taper it from its original small diameter to say 3". That second conical straw would have much less flow restriction than the original small diameter straw eventhough the final diameter before the inlet is the same.
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