Thanks to everyone for taking the time to weigh in. MrCrowley: that makes perfect sense! I think I was just staring at the problem for too long. Seems obvious now. Anyway, last week I increased the piston housing/upper tee to 1 1/4" to accommodate a bigger piston and... Success!!! I got it to throw ...

Piston is 1" OD. Port is 1/4" ID. I assume there is a desired ratio that I am not aware of. I had to build this on a budget so most of the materials were already on hand. I'm planning on machining a new brass port to replace the brass fitting shown in the pic. Any input is greatly appreciated.

I'll upload pics and info when I get off work. Thanks for the quick reply!

I am a new member and I would just like to say, thank you for posting this! I have been building combustion launchers for the past 20 years and with your help, I've completed my first hybrid. This build has been a blast. My first question is, where I might I find info on piston valve psi? I have yet...