To get full speed, the engine must be turning 3600rpms. Are you splitting with the engine rev'ed all the way up.
What size hoses are between the control valve and the cylinder. To get max flow you need at least 3/4 hose's. Yea you can flow 16gpm thru a 1/2 hose, but you will not see the benefits of the high flow on the return stroke running small hoses. Your pumping 16 gpm into the rod side for return, but you will have a lot more flowing out of the piston end of that cylinder, 1/2inch hose just slows you down.
Also what is the flow rate on your control valve, if you dont have a 25gpm rated valve, wont do you much good to increase hose size, it will still be restricted at the control valve. You might be able to plumb in a dump valve on the return of the cylinder that lets the oil bypass the control valve and go directly to tank.
To get any real speed out of your cylinder, you probably need a bigger pump, my 5in bore, with 28gpm pump has a cycle time of 12sec. Mute point if your control valve wont handle the flow you already have.
Cheapest fix, besides taking it back where you bought it, would be to downsize cylinder as had already been suggested. I used to split everything with a 4in cylinder and 14gpm pump. I had a 4way adjustable wedge, with a 24in tall blade. Only stuck it once and that was on a 30in dia piece of green white oak that had 4 large knots in it, reversed the round and it split right thru it, 4ways. I have split close to a full cord in about 15min, and worked the ####ens out of 5 people with that setup. I only went with a 5in cyl because I now split 6 ways, with plans for a 10way wedge.
opcorn:
