75hp versus 70hp which one

[stickbow]

I have recently purchased 3 motors. Two and a half 1978 75 horse evinrudes (one in parts) and one 1984 70 horse evinrude. Now I know all of the normal things will need checked, compression and all, to make the judgement of which one to keep as my boat motor, but is there any pros and cons to the two different models and years. They look to be on identical platforms, 3 cylinder, and on a quick look they even appear to have similar electronics. They were all used in a limited service, (owned by the state) on dnr and lake patrol watercraft. I expect they will all have little hours on them and not extremely hard hours at that. The starter teeth and flywheel show me that. Is there anyone out there that can give me a nudge toward one or the other.

Also if I read all the past post here correctly in 1983 the hp rating was changed. Is the 70 actually more motor than the 75's?

Thanks Brian

 

[Chinewalker]

Re: 75hp versus 70hp which one

Hi Brian,
The HP rating was in 1985, not 1983, so your 75 is a smidge more than the 70 in terms of wide open horsepower. How it gets there is the difference. The 75 is ported slightly differently and the end result is that it makes a bit better "fast" boat motor at the expense of a little bit of low-end grunt. The 70 may give up a little top end but makes up for it with a little better kick getting out of the hole. This is done primarily with porting as the 70 and 75 blocks are different. I have a 1980 75hp on one of my boats and it has been a great motor. When I say "little" bit in terms of the differences, there really is very little on either end. The low end grunt may mean the difference between being able to pop out a 220 lb. slalom skier or think about it a bit first. The 75 will still get the big boy out, but it'll just take longer. The top end may be the difference between 36 mph and 38 mph - something you'd likely not even notice by the seat of your pants....

- Scott

 

[stickbow]

Re: 75hp versus 70hp which one

Well I really appreciate the insight. Sounds as if I should go with the 75 since I have the parts motor and all. It came with all the electronics, (coils flywheel and pickup), and the extra block. Funny thing is the "main" motor of the sale, the one they just removed from service, looks to have the most amount of wear. So the decision should be between the two others! I am mounting on a 1978 Lund that currently has a 50hp merc. Very light boat as is and has a 75hp max rating.

Thnaks

Brian

 

[stickbow]

Re: 75hp versus 70hp which one

Hey Scott,

Was wanting to tap in to your knowledge a bit more. I have it narrowed it down to one of the 75's and the 70. The 70 is a 1984 and the 75 a 1978. I have did the compression on both and they are both around 130 across the board. My question is on the fuel delivery system and ignition systems. The type I carbs and coils compared to the type III carbs and coils and additional imput on these particular systems. I have done a bit of research and found the type ones have a fixed low end jet system with a high speed adjustable compared to the type III with 3 different orifices, low, intermediate, and high speed. What do ya think of the two different systems and ignitions.
Thanks Brian

 

[gotboostedvr6]

Re: 75hp versus 70hp which one

Use the 70. Reasons being that it has the better carbs, and electrical system. it also will most likely have a higher output stator.

keep the other motors for doners

 

[Chinewalker]

Re: 75hp versus 70hp which one

I agree. The 3-jet carbs are superior to the 2-jet carbs. Better performance across the board...
- Scott

 

[stickbow]

Re: 75hp versus 70hp which one

Thanks guys,

Funny my 10 year old captain has been lobbying for the 70 from the start. Says he has a good feeling about it! LOL

 

[gotboostedvr6]

Re: 75hp versus 70hp which one

any news?

 

[tashasdaddy]

Re: 75hp versus 70hp which one

we have a 14 year old member, that i would take his advice. so your son may not be wrong.

 

[Dhadley]

Re: 75hp versus 70hp which one

The other difference is the heads. The porting is so close that if you put the 75 head on the 70 you may not see any difference between the 2 unless you have something like a small Allison that responds well to very small torque differences.

On some boat designs you won't see any difference between a 70 and the 75. The one that had the most significant porting difference was a 1975 75hp.

Because it's newer, I'd go with the 70. After it's set up the way you want it, you might switch heads just to see if there's any noticable difference.