Welcome to the Forum. There is an awesome thread that covers the Patty from head to tow...imagine the real Patty from head to tow
http://www.rcuniverse.com/forum/GP_P...1027454/tm.htm

There are a lot of engines that work on this ARF. Here is a list of good ones. 3W 40,50cc, FPE 2.4,3.2. DA-50, Brison 2.4,3.2, ZDZ 40,50. BME-50.

I'd go with DA-50. The ZDZ 40 has a lot of power for a 40cc. I agree with the above post, 50cc and light. Most people's Pattys are coming in around the 16-17 lb range so a 50cc would be best for 3D...IMO