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      05-04-2009, 10:04 PM   #69
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Drives: 2011 BMW 550i M-Sport
Join Date: May 2009
Location: South Florida

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Originally Posted by A418t81 View Post
Couple issues with above:

1. Your calculations make some assumptions that aren't true. The main one being that N54s run anything more than about 10-11 psi at 6500 rpm. Boost ramp down after 6k is precipitous regardless of what it was prior to 6k. Figure 17 psi at 6k, but even that is pushing it. Most 17 psi power runs tend to make peak power at around 5500 rpm, if on 100+ octane and basic supporting mods = ~410 whp, give or take 10 whp.
Many people have documented 13psi of boost above 6000rpm on these engines with piggybacks and non-stock software. Just a few posts before this one is a prime example. So my example of 13psi in the intake manifold is very much valid.

2. Most running that amount of boost are going to aftermarket intercoolers that are looking at 1-1.5 psi of pressure drop at MOST at those flow values (~42 lb/min). That's hardly the ~5 psi you are using. Frankly, I don't agree with the nearly 3 psi pressure drop across the IC at stock boost pressures that you are figuring either, and neither does the pressure testing data that has been carried out on the stock IC vs. upgraded ones as far as before and after comparisons.
The pressure drop from turbo to intake is not just dependent on the intercooler, but also the pipes connecting everything together. You have to think of it as a *system* of parts. And just cause you don't agree with my numbers, doesn't make them wrong. My numbers are based on BMW's design figures and physics, both implemented using simple math. If you have actual test data to refute it, then by all means post it. But saying *you think* something is wrong, but not being able to back up your statement with simple math or documented testing, won't get you too far