Pratt & Whitney R-4360

The Pratt & Whitney R-4360 "Wasp Major" was the largest  aircraft piston engine to be mass produced in the United States. Although it found extensive military application, its 28 cylinders, 56 manually-adjustable valves, and 56 spark plugs prevented it from finding favor with the airlines.


R-4360 Firing Order

Cylinder rows are designated A through D from anti-propeller end to propeller end. Cylinder banks are designated 1 through 7, with numbers increasing clockwise, cylinder 1 being the topmost cylinder. Master rods are located in cylinders A7, B4, C4 and D1.


R-4360 Cutaway at the Museum of Flight, Seattle, Washington
Submitted by Robert Wahlgren



C-97 QEC, R-4360-59B Specifications
Courtesy of Robert S. Wahlgren

Weight with propeller7,988 lb
Weight without propeller6,500 lb
Displacement4,360 in³
Compression Ratio6.7:1
Propeller Shaft Rotation Clockwise, 0.375:1 ratio
Spline size60-A
Maximum dry weight3,691 lb
CG from main crankcase rear face18.4"
CG at crankshaft@ Centerline
Impeller diameter14"
Impeller Ratio6.375:1
Carburetor Bendix PR100B3-4
MagnetoScintilla S14RN-15
Magneto Ratio0.875:1
Spark plug gap0.011" - 0.014"
Spark Advance Normal20° BTC
Spark Advance Cruise30° BTC
Cam Timing
Intake Opens64° BTC
Intake Closes76° ABC
Exhaust Opens135° BBC
Exhaust Closes79° ATC
Intake Duration320°
Exhaust Duration394°
Cold valve clearance, not incorporating overhaul change 273
Cold valve clearance incorporating overhaul change 273


R-4360 Valve Gear Development

R-4360 Cutaway Preparation

Index of Wasp Major and R-4360 Designated Engines (568K Acrobat File)

History of the R-4360 (764K Acrobat File)

R-4360 Service History for C-97 and KC-97 Aircraft in Air National Guard Units


Ford-Built R-4360s

R-4360 Gallery (Warning! Large Files)