Looking for blower suggestions on a two laser setup.

Our current setup works well for engraving but we're starting to cut more now, and I'm noticing smoke in the cabinet indicating I need more flow.

Here is our current setup: 4" duct 20 foot in from the window connected to blower then another 14 foot of duct, y adapter, then another 6 foot to each of the 2 machines. So about 40' of 4" duct total, in-port on laser is 4" as well. Here is the blower we're using: http://www.harborfreight.com/2-hp-industrial-5-micron-dust-collector-97869.html\

Can you guys A) suggest a better blower for the 2 laser setup we're doing that will get that smoke out quicker?