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    Calculating Volumetric Efficiency (VE)

    Right, so the m106 system is in the process of getting squeezed in to the e30 bay, and I'm limited in the available space for an air filter. After searching through K&Ns database of universal filters I believe I've found one that will fit, p/n SN-2620. This filter is rated at 396 CFM (cubic feet per minute), which is on the low side for most automotive applications. Given that a normally stock m30 would have a VE of approximately 80% (.80), that leads me to a CFM rate of about:

    214 cubic inches * 6500rpm * 0.80VE = 342 CFM
    3456

    However turbo engines have higher VEs than NA engines, and therefor I need a different VE number for the m106 setup. Without the ability to scan an OBD2 system for things like fuel flow rate or MAP, I don't have the standard inputs I would need to calculate VE from scratch.

    Can anyone with more turbo building experience help me estimate the VE on a setup like this? Or does anyone happen to know the VE of the m106 motor? It doesn't have to be exact, but the difference between a VE of 1.2 and 1.6 would be significant.

    #2
    sounds like the biggest filter you can fit is as best you can do
    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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      #3
      Well if the biggest filter I can fit is still too small, then I need to really re-examine how it's all laid out.

      I did find another filter that I think will work. Called K&N and they confirmed it is rated to 535CFM, so that should give me a nice margin. I might just have to buy it and try it, at least with Prime I can return it free of charge if it doesn't work: http://www.amazon.com/dp/B000E7H3OA/...I2PRGXYKJMJUUW

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        #4
        for the purposes of sizing a filter you can roughly equate hp and flow, so if you want to make twice the hp of the NA engine it requires about twice the flow or twice the VE. can probably just prorate it

        problem with things like this is that for sure it might be a bit too small so you might lose some hp but it may not be enough to worry about but i wouldn't get too worried if the filter doesn't quite match what the equation says it should
        89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

        new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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