VERY, VERY cool 911/993 engine based airplane:
http://www.pbase.com/9146gt/my_9146_gt_project_3xltr_twinplug_engine_heads
A snippet:
"These are very unusual and extremely rare Porsche 911 cylinder heads. These are genuine factory-made twin-plug heads originally used on the Porsche 933 engine used in the PFM 3200 airplane produced in 1986. The engine was basically a CIS-adapted version of the venerable 3.2L engine. The engine used twin-plug ignition to satisfy aviation requirements that dual, redundant ignitions systems exist on single engine airplane engines. The valve sizes are standard huge 3.2 valves - 49mm intake, and 41.5mm exhaust. The ports measure 41mm intake and 38mm exhasut - larger than the standard 3.2 Carrera engine (40/38). Note the "exhaust-ring insert built-in to the exhaust ports. Four of the set of six heads are in super-excellent condition and look almost new while the other two were obviously run, there is a buildup of extrenge color carbon on them (different than normal automotive applications). These heads appear to have a "knock-sensor" built-in (the 3.6 "knock-sensor" is mounted over the cylinders, and doesn't always work perfectly). As indicated on the photos, the sensor is mounted off to the side of the cylinder head. These heads came from the former"
Here's the Porsche powered Rotorcycle (Helicopter):
Brochure:
http://www.gyrodynehelicopters.com/brochure.htm
History:
http://www.gyrodynehelicopters.com/xron_history.htm
Pics of NOS Helicopter engine:
http://www.356a.com/helicopter.htm