Converting 85hp to 125hp

Hello all. I have a 1970 Evin. V4 85hp but would like a little more power but I really like the hydroelectric lower unit which works very well. I have been told that of the years that are similar to my motor which I think are 68-72, that the V4 71-72 motors came in a maximum of 125hp models which I would like to switch out my 85hp power head with a 125hp powerhead. Is there a greater horsepower powerhead that I can use on my case? Has anyone out there ever made a conversion like this. Thank You all very much!

Re: Converting 85hp to 125hp

i beleive the 85, 100, and 125 were "the same".... but the old omc site says they only made 85hp and 100hp that year... old omc site <br /><br />(EDIT: Tsk, tsk, PMM. you know better than to offer to sell here.)

Re: Converting 85hp to 125hp

Any of the 1969-72 V4 powerheads 85/100/115/125 will swap. There are only minor differences in displacment between them (range from 94 to 100 cubics inches). The 115s and 125s run bigger carbs (1 5/16 versus the 85hp 1 3/16), not sure what the other differences are, presumably mostly porting. Those differences move the power up the rpm band, which means the 85 will have a fatter midrange, and the 115/125s have more top end. You may not feel a huge difference on your boat, particularly if your aim is to pop up skiers or push a big boat, rather than just top end speed. I have run a few examples of both on the same test prop, and can tell you that on the top end there IS a substantial difference between the 85s and the 115s. <br /><br />You might try just a pair of 1 5/16 carbs (I have a pair off a 125 for $20 if you want to try them, jslobvan@exit3.com). HOWEVER, first make sure your current rig is optimized. The motor wants to be as high on the transom as possible, without losing water pressure or cavitating the prop too bad on turns. Once there, prop is to turn at least mid5000s with you alone in the boat. <br /><br />If the powerheads are both freshwater & not too corroded, swapping them off isn't too big of a job.

Re: Converting 85hp to 125hp

Hi Johnnn<br />The difference in performance between a 85 and a 125 is GREAT. I had a 72 125 "rude" on a '73 V186 Glastron Swinger and a buddy had a 73 85 Evinrude on a V178 Glastron. My all-out front tank empty, 1 person 4th pin-hole top out balls to the wall top speed was an indicated 44 mph. His was 37. He was never able to break that 40 mark. Johnn these are great motors but the money required to do this up-grade may not be something you would consider; however, it is doable and would wake your hull up. You may try a newer post 1985 90 horse. These prop rated motors will fly!!!!!<br />Have fun<br />LW

Re: Converting 85hp to 125hp

Fairfield? Fairfield? You do all your high-speed runnin' on Red Lake? <br /><br />c/6<br />Hooty

Re: Converting 85hp to 125hp

To all who have replied to my post, THANK YOU! I have been spending hours researching my upgrade talking to omc people and I have learned from one gentleman that the 115hp motor is more powerful than the 125hp because apparently evinrude rated the 125 a horsepower from the crankshaft whereas the 115 was rated from the propeller shaft. I also learned that I could use a 135 or 140hp powerhead up to 1976 aslong as it accomidated the 4 spline shaft (apparently it will bolt up to my case, exhaust plate must be sinmilar or switched(?)). Also I am told that other than slight displacment differences and carb and jetting differences, they are essentially the same motors except for porting differences which I would have to do, but dont have a pattern. I als learned that on some v4 80&85hp reed blocks, several of the reeds may be plugged to restrict flow. Does any of this sound accurate? Thank you all for the advice!

Re: Converting 85hp to 125hp

Dear ledgefinder, Thanks for your reply. Top end is all I want. I have decided I will never be a water skiier. I have this motor on a 17' 1970 Kona fiberglass boat (Low Vee?)My speedo reads about 37mph at 5000rpm with a 17 pitch prop.Thanks for the offer of the carbs. As soon as I figure out the best way to upgrade this I may contact you about the carbs, Again, thanks, John