The Irwin 79 cylinders are composd of a nickel cast iron barrel over which an aluminium alloy cylinder is shrunk and doweled. Valve seats are of cast iron shrunk and doweled in place. The crankcase assembly is composed of two major castings of aluminium alloy.
The crankshaft is made from special het treated chrome nickel seel, machined and ground from a solid billet weighing approximately 90 lb, while the finished shaft weighs 6 1/5 lb.
Alloy steel heat treated connecting rods of H section are fitted with bronze gudgeon pin bushings. Pistons of aluminium alloy are fitted with full floating nickel steel hollow gudgeon pins. The main bearings are ball race typ, lubricated under pressure.
Accessories available at extra cost were a propeller and tachometer.
Type: 4 cylinder air cooled radial
Commercial Rating: 20 hp at 1730 rpm
Displacement: 79 cu.in
Compression ratio: 4.9-1
Bore: 2 7/8 in
Stroke: 2 3/4 in
Length: 18 in
Diameter: 23 in
Weight: 58 lb
Fuel consumption: not more than .50 lb/hp/hr
Oil consumption: not more than .06 lb/hp/hr
Lubrication: Jet spray cylinder walls an pressure to main bearings
Ignition: 1 Bosch
Carburation: 1 Winfield
Spark plugs: 1 per cylinder Robert Bosch