difference between 25 and 35 hps

[zpd307]

hello, new here. i hope you can help me with this. what is the difference between a 88 johnson 25 and 35 hp.
my story is: i have an 88 johnson 25hp. its a short shaft tiller that is mounted to my lowe 1648 modified v. the boat and motor are my duck hunting and fishing rig. anyway, i have never been satisfied the the 25s performance when i attached it to the new boat when i got it. it doesnt seem to plane which causes us to get wet from the spray. it is especially bad during duck season when the boat is more loaded with gear. i had tried different pitch props. it had 120 psi compression in both holes and seemed healthy. back to topic. the water pump fried last fall and overheated the powerhead. since i need a new motor i planned to upgrade to a 35hp. i know the 25 and 35 have the same bore. is the stroke different. i thought the carbs may be different but the local johnson dealer looked up a bunch of part numbers and they are the same for both motors. ie; carb, jets, exhaust leg, pistons. he thought that the 35 was able to rev up higher to make more power.
i picked up a 35 powerhead, but since everything is apart, i am now planning on rebuilding for a piece of mind.
so what makes the 35 different from the 25. thanks and sorry for the long first post. gary

 

[tashasdaddy]

Re: difference between 25 and 35 hps

porting, stroke lots of hidden things,

 

[BoatBuoy]

Re: difference between 25 and 35 hps

You can compare parts here http://12.2.215.22/pub/default.asp?SessionId=fa703a8db5294b4282305294722b5813&Lang=EN&brands=EJ

I took a quick look and some of the differences are the exhaust scavenger, crankshaft, carb, intake manifold. Some significant components that are the same are pistons, block, head. I would agree that the differences are minimal, and if tested, they may not be 10 horsepower apart.

EDIT:

...but the local johnson dealer looked up a bunch of part numbers and they are the same for both motors. ie; carb, jets, exhaust leg, pistons.

According to the Evinrude website, the carbs are different part numbers, as are the high-speed jets(orfice plug), and exhaust tube. The pistons are the same part number.

porting, stroke lots of hidden things,

Since the blocks are the same part number, the ports have to be the same in size anyway. "lots of hidden things" - now that's real helpful. Were you ever in marketing?

 

[F_R]

Re: difference between 25 and 35 hps

I only spent a few minutes looking and comparing, but I found a different carburetor, different intake manifold, different reed plate. The cylinder and crankcase gets a mite confusing because they vary according to model number and I didn't follow through on it.

As for the final power output, I don't know how they compare. My guess is that on an underpowered boat you won't see a huge difference. I do know that on the right boat the 35 will scream and Git! Mine turns 6000 rpm with a 17" SST prop. I don't have a GPS so don't know how fast it goes.

 

[zpd307]

Re: difference between 25 and 35 hps

what is the stroke on the 25 compared to the 35. i couldnt find it on the net anywhere. i do know that the intake is the same. both were pulled and compared. they had the same bore size. reed cage looks thae same also. that was why i had initially thought carb. the more air in, more power. if i knew what the bore on a 35 carb was, i could compare to my 25. the dealer had told me that there were different part numbers between different models. ie; flywheel is going to be different when comparing an electric start motor, it will have teeth, to a rope start, mine does not have teeth. there were two carb numbers. one for those with electric choke and one with fuel primer, mine uses a primer. do both the 25 and 35 have the same idle and wot timing, i am not sure it that would make a difference anyway. i saw in an old post while searching, that operating rpms on the 25 was 4500-5000 and the 35 was 5000-5500. i know these motors rev but 10 horses in an extra 500 rpms?

 

[zpd307]

Re: difference between 25 and 35 hps

i checked the brp.com website and compared part numbers. i am confused as to where everyone is getting their information. from what i saw, everything is the same; exhaust tube, exhaust covers-both inner and outer, float chamber, crankshaft, rods, ignition, leaf plate, leaf valves, etc... except; intake, and carb. i saved the parts to the list, one list for each motor, and then compared them side by side. it seems as though the 20 and 25 share a carb and the 30 and 35 share a carb.

 

[Tinman57]

Re: difference between 25 and 35 hps

I had a 1988 Evinrude 20 hp that I had a mechanic uprate to a 25. As I recall, the only change was an intake manifold. The power increase was dramatic and the uprated motor served me well for 15 years.

However, the mechanic said it is much more complicated to uprate a 25 to a 35, and that it probably isn't worth it.