Continental 65 HP or more, Ok on Model 4 ????

[DBVZ]

3400 or 3600 depending on which one. Or so the web site says. It is interesting that the reduction gear results in an increase in thrust. 3600 RPM means the prop length is limited to keep the tip speed under limits (fixed pitch, wood). Interesting stuff. Lots to consider in picking an engine and prop combination. The engine MFG says the VW direct drive requires a wood fixed pitch, so if you really want a ground or air adjustable you need to consider other combinations.

Front Drive - Air-Cooled.
Direct drive, driven off the pulley end (Type 1 only) for standard aircraft configuration. The Front Drive engine turns counter clockwise from the cockpit in a tractor configuration. Wooden props ONLY must be used. This is the most popular configuration.

And here: http://www.greatplainsas.com/gpasproducts.html