does any one know if you will see a big improvement in performance by upgrading from the 31 to the 35

You will likely gain about 4 hp

Same block. Just build yours up.

did not know what would one do to build one up

No, I wouldn't bother upgrading or tinkering with it. I've seen your boat with a 31 scoot with 4 big guys in.

To build it up to a stock 35, you would need the 35 Crank, pistons, rods, and carb. Everything is interchangeable, and all the parts other than those listed are the same on your motor.

An aftermarket cam, some headwork, and a 35 carb would likely get you in the same ball park power range for less money. My guess is those mods would actually get you a little stronger motor than a stock 35. An aftermarket exhaust would be a good thing to add also if you don't already have one. Any aftermarket parts for the 35 will fit your engine (other than the pistons/rods unless you swap the crank out at the same time).

Bore is the same between the 31 and the 35 so pistons will interchange. Stroke is different, so a 35 crank would be needed if you wanted to go to a 35, Carb is different. I don't know if the the rods are the same, but I think they might be.

I would leave the 31 crank in it.

Add a cam, a 35 carb,exhaust, and do some flow work and a light decking on your heads and that will put you up past any 35.


The shorter stroke on a 31 will wrap up to top RPM faster.

Best hot rod motor I built was a 31. Ran same top end as my 35 but was smoother with quicker throttle response.