Microlighters

I am building a PERIS JN-1. This is similar to the Koala.
Plans suggest a 40hp engine.
Cruse 60 mph (94Kmph) Climb 42mph (45Kmph).
Empty weight 146kg
Gross weight 272kg
Prop 52 inch Pitch 27inch.
I want to fit Rotax 504 DCDI. This will be a slightly more powerfull engine.
Can someone advise me on how to match gearbox and prop?

Speak to Piet Prop, He is a fundi in matching props to engines.

Pieter de Necker o11 sewe 93fyf 235

Regards

As far as I can see the Rotax 504 is a 4 stroke motorcycle engine producing only 30hp. Are you sure about the engine or you did not mean 503? With the 503 the best choice is C or E box. The C box does not have an electric start and the E box does.