Biggest Diameter prop for volvo 290 leg

Hi there,what is the biggest diameter prop I can get onto a 290 leg? I have an 8.3L cummins hooked to one and need the big diameter to try to keep the pitch sensible.thinking 4 blade as well to help the cruise economy.
Regards doug

 

16 inches...... and what kind of Cummins 8.3l? Power@rpm's?

 

Hi,thanks for that,its a v504m v8 with under 400 hrs on it.215hp @ 3300 rpm max,198 @ 3000 light commercial,178hp@ 2800 24hr rating.I have posted a couple of pics of the boat and the engine installation in the powerboat section.
Doug

 

Ok Duggy, you are spinning two threads on the same issue, lets keep it to one or we oldtimers get confused...... See answer in the other t.