Allen’s most recent project involved building a custom 5.0 L (5000 cc/305 ci) V-twin engine from two Pratt & Whitney R1340 aircraft cylinders.
The rest of the components for the engine such as the crankshaft, con rods, and aluminum cast crankcase were hand-made by Allen.

He also built Millyard Viper V10 is a one-off motorcycle capable of over 200mph,
built by British engineer Allen Millyard, it has an 8-litre Dodge Viper V10-engine producing 500 bhp (370 kW)
The bike has been clocked at a top speed of 207