Evinrude 115 & 135 hp. Differences

[charliealley]

I have a '78 model 115 Evinrude. My manuals tell me the 135 has the same bore & stroke. I got a 135. The carbs are 1/8" larger, and the exhaust cover seems to have better flow charicteristics. Are there any other differences, port timing ect. Thanks for your help.
Charlie

 

[emdsapmgr]

Re: Evinrude 115 & 135 hp. Differences

The last year for the 135 was 1976. In addition to the larger carbs and the bubble back exhaust which you noted, the blocks two blocks have different porting characteristics. Also, the 135 has higher compression heads than the 115. Your 78 115 does have the rubber intake filler blocks (considered worth 3-5 hp) which the older 135's did not have.

 

[charliealley]

Re: Evinrude 115 & 135 hp. Differences

Thanks for the reply, as i said I have the whole 135 engine. I noticed the rubber blocks in the intake of the 135. Wondered what they did. So do I understand you that the 135 has a higher compression ratio. If I swap heads will I get it or is the difference in the piston dome.
Thanks again, Charlie

 

[charliealley]

Re: Evinrude 115 & 135 hp. Differences

One other thing the improved porting charicteristics you mentioned. is that from actual port timing in the cylinder or is it just the shape of the port in the transfer port covers. Thanks Charlie

 

[emdsapmgr]

Re: Evinrude 115 & 135 hp. Differences

Usually the high hp engines have the ports drilled a few thousandths closer to the top of the cylinder. This make the engine a "high port" engine. The high port engines don't have the hole shot of the low port engines, but will ususally run higher rpm's and that's where the extra hp comes in. High compression heads do help compensate for the high porting at the bottom end.

 

[charliealley]

Re: Evinrude 115 & 135 hp. Differences

Thanks for the help, I remember cutting ports on the yamaha motorcycles I used to race. Cutting ports had basicly the same effect as cams in four strokes, cut the top of the port, longer duration, cut the bottom, advance port timing. I'm just trying to get all I can out of this 115, by swapping parts with the 135. If I ever have to rebuild it maybe then we'll play with the die grinder. I think I'll CC the heads to find out any differences there.
Thanks Charlie

 

[emdsapmgr]

Re: Evinrude 115 & 135 hp. Differences

You can easily open up the intake and exhaust ports yourself. If you square off those holes, you will increase the flow through the powerhead-increasing performance. I would not enlarge the openings higher, but just square them off side to side. Make sure you hold a radius at the corners of the ports. As you square them off, you will also technically be raising the port timing very slightly-of little consequence, however any time you increase powerhead airflow, you need to consider jetting the carbs up slightly to flow more fuel.
You will definitedly need to jet up if you find a set of high compression heads.

 

[charliealley]

Re: Evinrude 115 & 135 hp. Differences

Thanks my friend, I have the 135 heads and carbs off the same engine so I'm hoping the jetting will be pretty close, should be easy to get readings on plugs since you can run a boat WOT. another thing when cutting ports. slightly radius the edge of the port so a ring don't catch on it. fine sandpaper will put enough radius. at least on motorcycle engines it was very important. I suppose boats too.

 

[emdsapmgr]

Re: Evinrude 115 & 135 hp. Differences

I would also not thin the vertical stock (bridges) between the ports. If they get too thin they can crack from the heat.

 

[charliealley]

Re: Evinrude 115 & 135 hp. Differences

Thanks Emdsapmgr, you've been a big help. We could have a great discussion on cutting ports but that would be another thread. You have an advantage on me though, My experience is on 12,000 RPM dirt bike engines, I'm not sure how it would relate to 5,500 RPM boat engines. Man I would love to sit down over coffee with you just to pick your brain. Thanks again, Charlie

 

[emdsapmgr]

Re: Evinrude 115 & 135 hp. Differences

If you port it and put the high compression heads on it, the powerhead should pull strong to 5900-6000 rpm. It runs out of the torque curve much over that, so I'd prop it to run up to 6000.