[THEFERMANATOR]

13.5X15 stainless will be about as big a prop as you want to run. That lower unit has a 2:1 gear ratio, and the 120 is a high RPM engine. A 19 pitch stainless will lug it down and possibly cause a powerhead failure. I would be surprised if it will get on plane with a heavy hull like a V-20 if it is indeed a 19 pitch prop. I know I ran a 19 pitch VIPER on my 140 on a 19 foot bowrider and topped out 56 MPH at 5600 after it was recupped. A 17 pitch stainless prop topped out at 49MPH on teh same boat at 6100RPM's(which was my rev limiter). A 15 pitch stainless is what I ran on the same engine on a 19 foot ANGLER center console and it ran pretty good.