There may be a few propping up coffee tables , they are fairly obsolete now as the F1 rules demand 10 cylinders max.

The Infineon/Hitex example is at the extreme end of this topic ,but noteworthy none the less.

If he is really interested in making this work he should use a single cylinder (lawnmower) engine to start with. If he can get that working ,then maybe he can progress onto four cylinders.