Just bought a used 16hp longtail. It came with a 8x8 prop on it. I saw on here where people say to run an 8x4 with the 16 horse. Is an 8x8 to much pitch?

I’m not a mud motor expert but my friends run longtails. Get a ruler and measure from the front of the prop to the back and multiply by 2 then add 1-2” depending on the cup. That should put you close to the actual pitch. Then measure outside distance that’s the diameter.

Since it’s a used prop it may be worn out and actually work well for you.

To answer your question I think you are over propped

Run it in open water and read your tach at WOT. Looking for 4000 rpm’s at WOT

Best of luck !

Will do. I am putting the tach on this week. A mechanic friend of mine checked the RPMs out of water and it was 3600 @ WOT. should I try to get more out of it?... Its a 16hp Vanguard

3600 is the correct setting for a stock motor, you can adjust the throttle stop and governor to get 4200 out of it and maybe see a little more speed in the water. In the water you should be running between 3600 and 4000 depending on how you have the governor set. You wont get more than 3600 set the way you are now.

Is it safe to go to 4000? Dont wanna pop it

Mine runs great at 3900 rpms. You can play it safe and go for 3600 all day long.

Max Speed = pitch (ft) x RPM x 60 min/hour x gear ratio (1) x .85 ( Prop slip .15) /5280

i.e.

pirop rpm speed slip final speed
4 3900 15 0.15 13
5 3800 18 0.15 15
6 3700 21 0.15 18
7 3600 24 0.15 20
8 3500 27 0.15 23

The trick is to find the best prop w/ less slip at your rpm but you need the HP to turn the prop.

Best of luck.

Got my RPMs up to 4400 out of the water. Is that to much or will I be ok?