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  1. #26
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    Click here to enlarge Originally Posted by Itsbrokeagain Click here to enlarge
    So how does speeding exhaust velocity up attribute to higher back pressure? I thought that as whatever fluid in motion increases in speed, pressure drops? How would keeping to a 3.5" pipe hurt over a 3.75?
    Speeding the fluid up increases pressure drop, the higher the velocity the higher the pressure drop. Even if the pressure level of the gas is less, the relationship between pressure drop and gas velocity is a square function. And moreso, the relationship between pressure drop and pipe diameter is a fifth power function. Guess what, double the pipe diameter and that is a 2^5 times less pressure drop, as an example, because of the reduced velocity and reduced relative roughness of the pipe (pipe surface roughness vs pipe diameter).
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  2. #27
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    Click here to enlarge Originally Posted by WDBi Click here to enlarge
    DBFIU what would the ideal exhaust system be for the n54 with stock turbos and would it change with rb's?
    Ideal exhaust system for the N54 with stock turbos is open downpipes. For RB's, same thing. Now, I dont suggest you do that unless you are certain you wont burn anything underneath the car because 1000F exhaust gases will be dumped out right behind the engine. But theoretically, to answer your question, open downpipes is ideal.
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  3. #28
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Ideal exhaust system for the N54 with stock turbos is open downpipes. For RB's, same thing. Now, I dont suggest you do that unless you are certain you wont burn anything underneath the car because 1000F exhaust gases will be dumped out right behind the engine. But theoretically, to answer your question, open downpipes is ideal.
    I guess this is why you are an engineer and I just install things LOL. I suck at math and your formulas are over my head lmao.

    I guess the cars need to be tuned specifically for open downpipes, as everyone who has tried that said the car was slower.

  4. #29
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    Click here to enlarge Originally Posted by Itsbrokeagain Click here to enlarge
    I guess this is why you are an engineer and I just install things LOL. I suck at math and your formulas are over my head lmao.

    I guess the cars need to be tuned specifically for open downpipes, as everyone who has tried that said the car was slower.
    I am sure the car would have to be tuned for that. Mechanically though, open pipes would be best.

    ECU Software though, is a whole different ballgame!
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  5. #30
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    I like the quick and to the point conclusion this thread reached.

    Expanding on the thread topic, what is the best Y pipe design? The type that merge and increase in diameter at the same time, like example 1, or the type the merge, and immediately following increase in diameter like example 2, or other?

    Ex. 1
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    Ex. 2
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  6. #31
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    For a turbo application where the gas is not flowing fully developed (it is swirling like a corkscrew) you would probably want example 2. The reason is, you want to get rid of the swirl velocity component as quickly as possible because that drives up backpressure, and having the expansion will help slow the flow down considerably which reduces pumping losses (which are exacerbated by corkscrew flow)...

    that's my opinion

    edit: note that in example 2, the expansion joint, the actual joint where the taper begins; has some expansion angle. That angle is CRUCIAL to the performance of a delivery setup like this. That angle needs to be 7 degrees (or 15 degrees total if you are measuring it form wall to wall of the pipe ID) or less for 'ideal' diffusion from a smaller pipe into a larger pipe, it can be more than 7 degrees but you will encounter flow separation at the ID walls of the tapered joint, and separation effectively impedes flow from exiting.
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  7. #32
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    well, my Y pipe didn't turn out uber awesome, but it should get the job done.

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  8. #33
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    dude it's fine, you don't need to make it a science project. That design fine.

    the extra work to get the last 10% of power out of an engine is 90% of the effort. And thats what costs lots of money and time.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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