there’s more than enough info on his site to try and recreate some of his experiments, but perhaps you should start here instead: How to Design, Build and Test Small Liquid-Fuel Rocket Engines.

How to build a transparent hybrid rocket engine using acrylic rod and a canister of oxygen, with a breakdown of how various other types of rocket engines work along the way. Consider supporting my ...

[Richard] does say making larger rocket engines out of 2 or 3-inch PVC may not make much sense due to the increased chamber pressures. There is a fairly clever reinforcement method for these PVC ...