Some creative engine builders have taken four Briggs & Stratton 6S engines and combined them into an inline-four engine. The 6S engine was made from 1949 until 1957, had a displacement of 6.28 ci (0.1 L / 102 cc) and made 1.6 horsepower at 3,200 rpm. Each engine was welded together including the cam and crankshaft into one engine with a 1-3-4-2 firing order. They made a custom intake manifold with a small motorcycle carb and a custom exhaust manifold. The distributor is from a 1926 Chevy car which is driven off the crankshaft. The builders estimate the engine makes around 4-5 horsepower total. There is 25 videos in the playlist so sit back and enjoy.
Source: 805 Road King Youtube channel via BangShift
I think i will try this with some 3.5 magnatrons