I have 1985 23 nova xl with a 5.7L 260hp mercruizer. Was wondering whats a good prop to run for this boat. I'm running a quicksilver 19 pitch only turning 4000rpms an about 43 mph on the gps. My boat should be around 4500 rpms.

Try a 17" pitch 3 blade; should move your RPM to 4400 or so.

I never heard of a sm block turning that low rpm 4400 to 4500 from merc, your putting a strain on the motor. I can check but I think 4700 would be about right. look for a used 17p ss prop from merc or hydromotive. if you can go new call bblsdes brett and go to his site you can see the different styles of props. brett has a swap program where you can try another prop. also make sure you trim out enough once on plane you can loose rpm by not running correct trim. good luck.