Final Verdict on Bellmouths?

[Huckster79]

Folks, I'm in the middle of my build, I am aiming for max efficiency.  I have read a ton on here and I have seen Bellmouths mentioned and discussion but haven't found the practical final verdict, I didn't see any posts after folks had experimented with them. 

I have one printed now for my 6" exhaust out of my Thein... I will experiment a bit on if it adds efficiency and will attempt to experiment on amount of dust that comes out the exhaust and such.  But curious what others real world experiences have been with the bell mouth and how they ultimately mounted it in what location above the baffle and such so I'm not starting out completely blind about the bell mouth...

[Huckster79]

Well, I found the bell mouth inside the the thein dropped my CFM significantly! at any height above the baffle.  I was getting 5500 fpm airflow with the straight pipe out of the top and just a chamfer edge on that hole in the top hat, so it already had a "mini bell mouth" that equates out to around 1150cfm.  With the bell mouth on the exhaust pipe, from 1.5" above thein to all the way to the top, it was around 4500fpm of velocity. 

My theory is this as to "why".  My bet is the bell mouth stats for efficiency are out of calm air, my guess is that big ol shape it introduced into the dust chamber make the air very turbulent inside instead of doing a toilet bowl swirl around the edges.

So I'm going straight out the top, I bondo-ed and really smoothed out the chamfered exit to flow right smooth to the pipe.  I used a lot of bondo in my thein build to make sure all was smooth. 

One efficiency spot I discovered that I haven't heard anyone mention, on the HF 2hp DC, which my guess is this will be true of all the different brand versions that look similar.  At the exhaust port of the impeller unit, the 4x6 hold was formed by bends and it created a spot the air would be hitting the open side of a "U" basically as it exited.  Mine is not that way anymore, a lil wire wheel and bondo and it in effect is a bell mouth exiting, so the air does not hit the back side of the "U" bend, it now is a smooth "ramp" on all sides leading to the 4x6 exit port.  Which I'm keeping 4x6 and not necking down to 5"