LEGO MOC V8 piston engine (6x6x5 studs) by SUPER8_LTG | Rebrickable - Build with LEGO
Amazon.com: Yanscian 6 Cylinder L6 Engine Model Building kit Set Hobby DIY STEM Toy for Kids & Adults with Guide 500+ Pieces, Toy Building Set, Build Your own Engine That Runs, Mini
Exploring Piston Engine Design With LEGO | Hackaday