20hp to 25hp or 35hp Conversion

Hi,
Some of you are probably groaning as I’m sure this topic has been covered extensively. I’ll keep this short and sweet: conversion for 80’s 2cyl 20hp seems very do-able and literature suggests that an u/g to 25 or 35 can be done. I’m leaning towards 35 given that work is the same (replace carb and intake manifold) except for the fact that 35 requires re-propping. Are there any gotchas here that would suggest that I should NOT go the route of the 35 upgrade? May come down to parts availability…

35's are not quite as good idling as the 30's. If your fishing with these motors, trolling slow, I actually prefer the 25's. Backtrolling is my preference in order to present the bait in an appropriate manner..If your trolling forward, like for lake trout and salmon which prefer a speed of two up to 2.5 mph it is almost impossible to maintain that speed with a 35. It also depends on what parts are available and how much you want to spend. If you want to just go fast then of course the 35 is the way to go. Since I run twin motors on most of my boats, I prefer the 25s and 30s, then it's easier to fish once you get to the area.

What is the model # of the motor that you want to up grade to 35 HP ?

racerone said:

what is the model # of the motor that you want to up grade to 35 hp ?

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timguy said:

35's are not quite as good idling as the 30's. If your fishing with these motors, trolling slow, I actually prefer the 25's. Backtrolling is my preference in order to present the bait in an appropriate manner..If your trolling forward, like for lake trout and salmon which prefer a speed of two up to 2.5 mph it is almost impossible to maintain that speed with a 35. It also depends on what parts are available and how much you want to spend. If you want to just go fast then of course the 35 is the way to go. Since I run twin motors on most of my boats, I prefer the 25s and 30s, then it's easier to fish once you get to the area.

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Wow, that's hardcore! Love the pics.

Thanks for the info. Definitely something to keep in mind. Here are my considerations:

1) I have a 25hp 3cyl already on the boat (love it!) - it also trolls pretty nicely
2) boat is rated for 40hp so I'm curious to see what more hp does for me (boat is a 14' Starcraft Mariner V tiller)
3) I got the 20hp specifically to get us into Algonquin Park in the spring where motor size is restricted to 20hp.
4) But...back to point #2...now that I've got the 20hp and I've found out I might be able to get 35 out of it well maybe it could become my primary motor. Honestly though, it would have to be a pretty smooth and quiet 35hp for me to trade that awesome 25hp 3 cyl.
5) I've got an aftermarket powertilt from CMC with a limit of 35hp so the converted 20hp could be a good fit.

I took your advice and went with the 20-30hp upgrade, Tim. A fellow named John in Lindsay ON, Canada has a collection of parts for the upgrade and had the 30hp parts on hand but no 35. We'll see how I do.

Side note: holy moly, this 20hp sure is heavy!!!

Yes, not like the sweet ole 22 cu inch. I got 35 horse stuff here, but I think the 30 will be pretty nice for what your doing. I'm building a 35 LS for a guy this spring, but it's for a runabout, an old Alumacraft. He doesn't intend to fish much with it.
Yup, my Dad always said, "steering wheels are for Cadillacs"....and "the best ride is in the stern"....and "furthermore, you can see what the hells going on in the boat". Guess I'm a "chip off the ole block"!