what prop should I use?
 

I just bought a 85 excalibur 27 speedster 6.5 beam with a 502 motor appears to have some work done, unsure of weight and HP has velvet drive with TRS out drive.

It has a left hand rotation 3 blade mirage 25p on it now. I seen 60mph on gps at approx 5200 rpm. would like to see in the area of 75 mph

any suggestions?

i think you need more power before you try for more prop. you could try a 27 but i think revs will drop, speed about the same, and harder to get up on plane. any more blade area will slow you down. very few single engine boats that size see 70+ without owner being sure LOTS of work was done to motor.

Your slip% is quite high. That will need to be attended to.
I feel 75 is a tough act. Call us if you desire and we can discuss it further.

Brett