I got this incredible model from TÃµnis Vanaselja (Estonia) @ http://grabcad.com/library/nitro-rc-car-engine-block , all credits for him.
The final print was so amuzing that I really recomend this print. Check out my pics.
Including Solidworks 2013 file with the full part and halves and my custom support if you want to use it.
These parts require supports. I generate small waves in the solidworks file attached, but are not present in STL files. I bet you better generate automatic support in your slicer software.
My print took 2h 26min in my Ecksbot.
Remove supports and super-glue it together. Avoid to glue from outside to avoid making your part white and ugly.