Case Pressure - Positive, Negative, Neutral

[AlgaeEater]

When it comes to case pressure I hear Neutral is the best.  I have a s340 and I'm had positive pressure for the most part (maybe a bit too much even).  My problem now, is that I've mounted a front radiator, thus taking up both front fan slots.  Now my case has negative pressure. 

I've tested smoke entering the back brackets, So I made some changes to eliminate the Negative Pressure by lowering the Exhaust fan speed.  My exhaust fans are now at 45% (500rpms) which I think is ALREADY too low.  But still the negative pressure is still there.

 

CASE:     2 Corsair AF120's on the back for case fans

INTAKE:  2 NZXT 140 'Aerp' Fans (Static Pressure), with  RADIATOR & NZXT x62 Kraken

GPU:        Msi GTX 970

[Glennieboyyy007]

neutral and positive are the best ones. you said you have 2 as intake. if you have 2 as exhaust is should be fine. if you want to be sure that you have positive air pressure, just put 2 fans in the front, with the rad (which you already have installed there) and have just one exhaust

[mikeeginger]

You want a bit of positive pressure to help prevent dust build up as quick 

[AlgaeEater]

Couple questions:

 

If I was to take one of the exhaust fans out.. Which would I take?  The back rear or the top rear? 

 

Also, if I had a single exhaust.. Could i just have the two exhaust fans at a lower rpm (half the rpm of a single) so the airflow would technically be the same