It seems like a year ago I was cruising The "Hitchhiker's Guide" to the Maxi-Stream mod at RC. These guys where getting incredible flow from MJ 400, 600, 900 and 1200 pumps, I thought I would look further into the post, then discovered it was like driving through New Mexico, a few cool sights but enough desert already, it was long. Finally I came across a post by a guy called Ball. He mod'ed a AC-70 and he claimed it put out 3000 gph. Being who I am, I had to try this; it sparked my DIY fever and tickled my cheap wallet. 3000 gph for under $50.00, they advertised. My final build price was about $65.00, but still this is better than a Tunse or Seo price tag.
I got the stuff and began to build, the shroud was a pain to say the least, I wasted about 6 of those 2" to 1.5" reducers before I figured how to cut the slots with out breaking them off. I used a miter saw in a rather dangerous way and do not want to be responsible for anyone loosing a finger, so this is done at your own risk. I locked the trigger in the on position locked the guard in the up position. I wrapped a piece of tape around the reducer at the large end, then marked tape every 3/8 inch, all the way around. I then took the reducer over to my table saw and set the fence about 1/8 inch from the blade and the blade about 1/16 inch high. I then put the big edge against the fence and moved it over the blade, then rotated the reducer until I had a slot all the way around the base of the reducer. I then took it to the miter saw and began cutting it on each mark, it helps if you do not cut the big end at the opening, I had to start on the large part and cut through to the shoulder. This takes some practice and is DANGEROUS, DO THIS AT YOUR OWN RISK AND KEEP YOUR FINGERS AWAY FROM THE BLADE. I cut two blade thicknesses at each mark. After the reducer is cut then I used a Dremel tool to remove enough of that base grove to allow the tabs on the AC to clear. This will allow the reducer to be lowered to the base of the pump and turned to lock. As for the shaft for the prop, I got a cheep plastic pen and some ro hose, I cut the pen so it was high enough to mount to the impeller magnet and the prop would be about 1/4 inch from the edge of the top of the reducer. I also cut a slot to fit the key on the impeller magnet. I inserted the ro hose into the pen and glued it with super glue. I then purchased a Sidwinder 1.5 x 1.5" prop from Great Planes Hobby, Part number GBMB 1090. I drilled it to accept a #8 nylon screw from Home Depot. I then glued the prop to the screw and the screw to the ro tubing. Check the rotation before you glue, assemble and test first. I then glued the prop shaft assembly to the magnet. You may have a problem with the rotation if so then you will need drill the side of the coupler just above the prop and insert a piece of ridged tubing to act as a stop. Put it together and let her roll.
Here are a few pics.
AC-70 Stream Mod 
These are the supplies that I used.
