Hi anthony,sorry to take so long to get back to you but I haven't been checking in here much lately. To answer your question a 1/2 vw engine is just that....a vw engine that has been cut in half.Some still use the full case and use block off plates to remove two cylinders,or as mine is done with the case cut off as well as the crankshaft and cam shaft.I use a two cylinder tractor magneto for ignition. It is fitted to the back of the crankshaft like a "real" aircraft engine. I have taken so long to get back to you that you may have already found all this out on your own. There is a section in the auto conversions about 1/2 vw engines.You can get more information there. BTW thanks for asking!