Just built one with a 13 hp eng got a 10x8 on a 1436. I think I got the gear ratio wrong though. Got 4" pulley on the eng and 4.5" on the prop, which comes out to 1.1 to 1. I am only seeing 8mph out of it. My question is do I need to go to a 1.5 to 1 and will it help out on speed and maybe pick up the back of the boat some as it seems to drag.

Your gear ratio is a bit high. Drop it 1.5:1 as you stated. The motor probably isn't able to get to it's peak torque and you are not getting on plane. Once you get the drive ratio figured out, your speed and the "dragging" of the back of the boat will improve. The 16 hp that I built this last summer will push a 1436 with 400 lbs in it nearly 22 mph. This is running a 10X8 prop.

Post up some pictures of your build.

Mag10

Do you know where I could get just a shaft for my surface drive I'm building need a 3/4 x10

I got the 13 hp honda tricked out and ended up with the 10x6 hopkins. My gear ratio is 1.2/1 (36top 44 bott)on Alumacraft 1442.

The 10X6 is slow but has power for three guys. Great with 2 guys.

I tried the 9X9, 9x10, 15-60% slip under load.

Hopkins 10x6 got 6% slip. Based on my own calcs and tested today.

I finished building a 16hp short tail earlier this year and it has run great. I run a 1.6 to 1 but after the split I think I will switch to a 1.5 to 1 or even a 1.4 to 1. im also running a 10x8 prop. On a very heavy, old and beat up 14x48 lowe jon.

Ive removed the governor, modified the intake and built a custom exhaust

Free spinning it will turn close to 5500 rpm (way to much for that little engine)

The way I have it know I get about 16 to 17 with just me and no gear and turn 4800rpm
12 to 14 mph loaded with gear and 1 person and a dog and turn around 3900 rpm
8 to 10 mph with it loaded to the top and 2 guys and a dog. and turn around 3300 rpm