I'm going to have to disagree with this statement to a certain extent. The 6.7 does not require a vacuum to keep crankcase pressures in check.
There is a huge difference between engines that have a vacuum pump and ones that simply vent to the intake in a diesel application (gas engines are a different animal).
It's easy to see my point when you look at how the system works. In order for the engine to pull a significant amount of vacuum via the intake, there must be a restriction of some sort. The only place for there to be a viable restriction is the intake filter itself. Because there is a small amount of restriction caused by a filter, you will naturally get a very small amount of vacuum but it's negligible at most. The only way to get enough vacuum from the intake system to show performance advantages would be to run a more restrictive filter which would net more power loss than running little to no vacuum at all.
Hope that helps!
My post was rather vague. I agree with you. The small portion I added was "the added benifit" a negative crankcase pressure reduces many oil leaks around non-pressurized sealing areas.
Truthfully I'm not sure whether our 6.7L crankcase is +/- during running condition. I can only assume it's negative being it has a "draw" I'm not debating the issue. On large HP engine (8,000+) they run a very slight negative pressure via vacuum pump. (Big enough to blow up a child's giant bouncy house).
This was heavily discussed awhile back when folks were adding venture tubes in the exhaust stream to scavenge crank case gases. However without rhe use of a manometer nobody truthfully knew what was going on! I'm not against a CCV aftermarket mod, just feel from an engineering standpoint the factory system netted the best results. "Feel" but no real data to say otherwise.
Do you guys have any data?
*** I wanted to add, that a manometer was truly the only way to test results from air filtration systems as well.. aftermarket or stock or whatever. However the dyno was used instead. With results nontheless... and not that it matters either. I was hoping for a simple vacuum test between the filter and turbo for TRUE data. In an industry where an air filter change requires $6,000 worth of filters, a highly calibrated transmitter measuring vacuum is used to test performance. I don't see why we couldn't use the same method for testing besides a yellow plastic indicator!
