I worked on tuning my Zuma. I have the head pipe a slip fit and it allows about 2" of movement. I first slid the pipe out. It really made the acceleration better. The top speed was one mph less. I moved the pipe in an inch from where I started with it. The machine really too a hit on acceleration and the top speed went up .6 mph to 48.6.

Perhaps I could lighten the rollers a bit and get the acceleration back. I had calculated that one inch is about a 4oo rpm peak change.

I am going to reassess my pipe design. My convergent cone is an average of 28 degrees. To my understanding a steep convergent cone will produce a strong reflection but over a narrow rpm range particularly in the rpm above the peak power rpm. It may also lead to increased temperature of the piston. I have not had problems with that issue.

I have decided to make a new convergent cone. I am designing for 18 degrees. Most formulas suggest between 14 and 20 degrees with the higher value for higher peaks.

Hopefully the engine will have a the ability stay in the powerband during the variator phase of running and then pull past the peak for top speed.