[Dave at Pelican Parts]

Definitely an "open question" on that. The -four can work, but will generally be very stressed by running on the track. You wind up having to do a lot of work to keep the motor together under sustained high-RPM and high-load situations, like driving on the track. The Six has far fewer issues with that, and they're all quite well understood by the 911 guys who have been making the engines live at the track for decades.

The four-cylinder motors tend to be less expensive (until you start really "building" one--then hang onto your wallet!) and they are definitely lighter. But I have the feeling that the 914-6 will wind up cheaper to run in the long term...

--DD