Well, as stated, I'm fairly new on the site. Been scrolling around for about a year, but just now making it on here. Not sure which section this belongs in , but this seems fitting. Now to my issues/project.

I've got a 1436 that was passed down to me , and have had a 15hp longtail on it for 3 years. I sold the motor, with the impulsive decision to try and build my own mud motor. I think I've decided to try and go towards a Surface Drive build.

I've been waiting on a deal for the "Predator" 22hp V-twin from harbor freight, and i'm trying to stay as low on cost as possible, and honestly for the price, I don't think you can beat it. (4000 max rpm) although i'm figuring its probably pushing more around 3700 consistent rpm at the shaft.

Although there's been multiple topics on it already, I just cant seem to find a straight forward answer to my main issue.

When running gear reductions, and whatnot. I planned originally on running a 4'' pulley on the motor shaft, and a 3'' or smaller on the prop shaft. In my mind , it made sense. Spinning the prop faster than the motor shaft would equal more speed, but not as much torque. Now after reading about 50 forums, I'm seeing that I should be going about this the opposite way as I am, And should be running a larger pulley on the prop. Therefore making my prop spin slower than the motor shaft.

Can anyone describe, or give me some insight on why this is? And also , in that case, what would be a good ratio to run? I'm not looking to be bashed , or anything like that. Just need some help understanding, from someone with more knowledge than myself.

Over gearing your prop will work if you want to run a really small prop, but then it won't get much "bite" in mud and you'll see a lot of prop slip killing your top speed. Think of your prop as the wheels on an offroad truck, if you put 13" wheels on it you can drive around in 3rd and 4th gear all the time, but you won't climb many hills or go thru much mud. But if you put 20" wheels with 40" tires and run it in 1st and 2nd or low range you can go almost anywhere. With a 22hp motor you can probably run an 11x10 or at least a 10x8 prop, but you need to gear down to get more torque at the propeller. As for gearing i would guess between 1.25 and 1.5 would be a good range. Most commercial builders use toothed serpentine belts and pulleys.

https://www.walkerindustrial.com/112872 ... m?CartID=2
https://www.walkerindustrial.com/146447 ... m?CartID=3
https://www.walkerindustrial.com/112867 ... m?CartID=1

These are just some examples. Good luck with your build

1) There is a coupon out right now for the predator V-twin. If you haven't got it or can't find it, lemme know.

2) Look at variable pitch pulleys or sometbing called a torque converter. Go to gopowersports.com and search TAV 40 series. Right now, the TAV 40 series pulleys are also on sale. There are a number of people using this with the Predator 22hp with good results although not on mud motors. These pulleys won't keep your cost down but for the money i think they offer way better performance than any engine mod. You'lltrain it get twice the low end torque, 25 -50% higher gearing on the high end but what i think is best about it is that the drive pulley is a centrifugal clutch that effectively gives you a neutral that actually works better than a true neutral as you never have to do any shifting. You can tap the throttle and ease through the timber or up to the dock without stopping and starting your motor constantly as you would with old school fixed pulleys.

Another point more toward your main question, is you don't need to decrease torque for the purpose of getting your boat up on a plane. Think of take off power as torque. If you were stuck in the mud would you want a trolling motor pulling you out, or a 37 hp Vanguard. Easy right, the 37 hp, but not because it has more hp exactly but because it has more torque although they are related and have a positive correlation. Putting a gear reduction on your motor means if you were to put a normal sized prop on it for the 22 hp, you may not have enough torque to get your boat to plane out, if you can still plane out taking off will be much harder on your motor, and speed in mud will be reduced or you'll just be stuck all together (probably stuck).