A good place to learn about log splitters is
www.northerntool.com
They sell a book how to build a log splitter.
I bought there book and built mine buying parts from them many years ago.
some key things to look at and learn about is the size ( diameter ) of the hydralic ram and what size pump ( GPM ) you'll need to make use of the size ram your using.
I went with a 4" dia. x 24" ram and a 16 gallon per minute pump, and a 8Hp engine. Its very fast and works great, but the 4" dia cylinder is a little week for big knotty pieces of firewood.
If I had to make a small living doing firewood, ( money not much of a concern ) I would have a 5" dia. cylinder and a 22 or 28 gpm pump.
Should mention that the only way to go is a two-stage pump, a single stage pump will be too slow.............
The diameter of the ram is your power and the size ( gpm ) of the pump is your speed of the ram.
Also you need the correct control valve ( for log splitters ) to make all this work safely and effeciantly.
Also, I run thin lightweight hydralic oil in the system to speed up things in cold weather.
go to this link and look it over, maybe get there catalog too.
http://www.northerntool.com/webapp/...ogId=4006970&PHOTOS=on&TEST=Y&categoryId=1465
Good luck...................