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Christ · 01-27-2009, 05:09 PM

Inducing vacuum in the cylinder before the valve opening event does two things - both of which are undesirable -

1. It makes for more pumping losses (try pulling two cups apart that fit perfectly in each other.)

2. It changes airflow profiles for an otherwise nicely tuned intake system, due to the vacuum caused by the cylinder being part way down with no air movement.. it would cause vacuum pulses in the intake that would ruin both harmonics (check the TB spacer thread) and the overall fluid dynamic profile of the intake itself by increasing the vacuum per intake stroke, in a pulse like fashion.

(#2 is partially speculative, and can't be held as gospel. Please research it before assuming it is correct.)

01-27-2009, 05:09 PM	#23 (permalink)
Christ Moderate your Moderation. Join Date: Nov 2008 Location: Troy, Pa. Posts: 8,919 Pasta - '96 Volkswagen Passat TDi 90 day: 45.22 mpg (US) Thanks: 1,369 Thanked 430 Times in 353 Posts	Inducing vacuum in the cylinder before the valve opening event does two things - both of which are undesirable - 1. It makes for more pumping losses (try pulling two cups apart that fit perfectly in each other.) 2. It changes airflow profiles for an otherwise nicely tuned intake system, due to the vacuum caused by the cylinder being part way down with no air movement.. it would cause vacuum pulses in the intake that would ruin both harmonics (check the TB spacer thread) and the overall fluid dynamic profile of the intake itself by increasing the vacuum per intake stroke, in a pulse like fashion. (#2 is partially speculative, and can't be held as gospel. Please research it before assuming it is correct.) __________________ "¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"