/sci/ - Science & Math

Last year I was trying to make an open-cycle rocket engine using hydrogen peroxide, but failed because 3D printed parts are fragile, leaky, take an eternity to print and are a pain to model (specially turbines).
I almost gave up until I had an idea last week: Instead of making a traditional turbopump, I could use piston designs for the pumps and the "turbine" (which now would be like a car engine), so I could use pvc pipes for the piston chambers and have way less 3D printed parts.
I'm working on it now but I noticed no real rocket engines utilize this design - why? Is it so inefficient it isn't worth it?
Also, any suggestions for the engine?