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      05-04-2009, 07:44 PM   #67
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smdandb2's Avatar

Drives: Blue One
Join Date: Jan 2008
Location: BYU

iTrader: (0)

So here it is. I am not a scientist, so I may call things wrong.

I'm not drawing a bunch of lines. Just plotting points and connecting some dots.

What Nick said above is correct. Its all math, but some assumptions were made. The VE is a variable for sure, but BMW documents show a VE that can be as high as +100% on the N54 (I'm glad I know people). I worked mostly with a 90% VE though. I did one plot of 94% VE, and you can see how it just makes the situation worse if you are trying to justify running them that high.

I put all the calculations on the image, so you can check my work if you want.

One thing that is getting disputed is the stock IC efficiency. Guess what? BMW has a map for this in MSD80/81. They tested it, and mapped it. Looking at multiple points (such as what Nick did) you can generate some equations to figure it out thru various PRs. Maybe BMW was off, but the fact remains there is SOME pressure loss.

But, I just stuck with 2psi drop thru the WHOLE system. Feel free to check my math and do a 3psi drop, its hilarious!

It's math, not rocket science.