Here's another rev of a couple of my favorite working Lego pneumatic engines, a new V8 and a smaller inline 4.  The new models sport several innovations that improve the balance in the crank and cam shafts (important if you have flexible shafts that suffer from torsion), and reduces the number of valves and moving parts.  The resulting models are smaller (cheaper), and much more efficient, producing a lot more torque per unit weight.