I'm getting a prop for my homebuilt 16hp longtail. Should I get an 8x4 or 9x5? Getting 4200 RPM out of the water.

I had a worn out 8x8 and only could get 3200ish RPM in the water.

Thanks

Im pushing a 14 ft. Riveted Polar Craft.

I don't know still depends a lot on what sort of water your in, just from dealing with the unmodified motor i have i would opt for the same thing but I'm in big water 90% of the time and have a sandy shallow bottom no mud and am no expert yet.
I've only just put a rev counter on my one so i don't know yet what revs its pulling but i'm changing a few things to make it spin harder/faster just because i can, however a small engine mechanic told me yesterday to remove the governor if I'm going to sit on it all the time to prevent the governor coming apart.

Here's a similar question from a week ago

viewtopic.php?f=3&t=35676

I threw a link of my brother and me testing my one in my neighbors duck pond, it would be 260kg of us and gear in the 12ft tinny V front

https://www.youtube.com/watch?v=HPZM-JmQrwY

Go 8x4... expecially if your 16hp is a single cylinder....

It's a Vanguard V-twin

Hang with the 8x4, we spin a 9x5 on a 20hp pretty well

Thanks SwampDonkey

Just got my BackH20 inc Prop in. Can't wait to try it tomorrow!

I went with the 8x4. Ran it today and I am pretty happy with it. I am getting my full RPM range now. I can actually get a little over 4000RPM. Should I be worried about my motor not lasting to long if I run it @ 4000RPM?

No