The Harmon Rocket seems on the face of things to be an attractive idea but the rear cockpit is very cramped and more important the RV4 it is derived from can have issues with the firewall structure, given the extra weight of the O-540 this is likely to be an issue even with the extra structure to support the bigger engine.
On the whole I think it is just a bit too much power and likely to upset the balance of the very nice RV4.
Last edited by A and C; 26th Mar 2013 at 10:18.