Check out this article at
RetroMechanix.com on the Boeing XB-44 Superfortress, a B-29A upgraded with Pratt & Whitney R-4360-33 Wasp Major radial engines of 3,000 hp each:
This experimental engine testbed first flew in May 1945 and was essentially the prototype for the B-50, the core of the USAF's early postwar strategic bombardment capability. The accompanying gallery features 15 high resolution photos of this little known member of the Superfortress family.
-Jared