1989 Evinrude 140 lower unit gear question

[Theoutdoorsman]

Just curious here, but might consider making some changes if the effort is worthwhile. I have a 1989 Evinrude planted on the transom of a 1978 model 17.5' Maidencract bass boat. I am currently turning a 19 pitch double-cupped steel wheel @ 6000 rpm's with a top end speed of approximately 46-49 mph, depending on my load. Honestly, I am quite satisfied with the overall performance. On the other hand, I am curious if there might be a way to get just a little more out of the outboard without jeapordizing the power head. Another 5mph on top end would be nice! Is it possible to swap the gears in the lower unit to achieve what I'd like? Do different ratio options even exist for this outboard? I have a hole shot that is out of this world, and could sacrifice a little if need be. (planes off in about 25 yrds) Maybe I'm looking in the wrong direction for what I want? A jack plate might be a better option? I'm looking for any thoughts on this from those with past experience in tweaking these older Evinrudes please. Even if the advice would be to leave it as is. Thanks for any tips or advice in advance!

 

[Haffiman]

Re: 1989 Evinrude 140 lower unit gear question

Try a 20" Raker prop. As is, you are above max rpm.

 

[Theoutdoorsman]

Re: 1989 Evinrude 140 lower unit gear question

The outboard, with an empty load on board, will turn 6000 rpm's at WOT. Normal everyday use, with two people on board, tackle, and the live well full, I usually turn 5600-5800 rpm's. According to my manual, this is well within specifications for the outboard at WOT. I can't imagine any performance benefit from simply changing to a Raker 13 1/2" X 20 pitch prop simply because it is considered a "high performance" prop. Experience tells me that my rpm's will decrease, making any performance gains null. Keep in mind, my steel prop has a double cup, and I think will perform much like the Raker and it's "high performance" cupping. Maybe I'm wrong to assume this? Though I've never tried the Raker, I seriously doubt I'd see a top end increase anywhere close to 5 mph. Wish it were that easy! I'm not interested in throwing money at it, only to find out later that I need to install a 6 inch jack plate and purchase a 21 pitch prop to achieve the desired results. Based on what past experience(s) can you suggest this "Raker Prop" purchase? This might be interesting.....

 

[Haffiman]

Re: 1989 Evinrude 140 lower unit gear question

This should by right be in the prop forum, but anyway.
Props are more than pitch, max performance is not always max rpm.
Your engine, if not mistaken, is rated 5000-6000rpm. It will give 140Hp @ 5500rpm. Anything above or below will normally reduce engine performance.
Next comes the prop designs itself. Raker, Cleever, Alu, SST, Cup, double-cups, 3-4 blade, optimum prop rpm range - you name it it is a variety of combinations.
Next are you running fresh water or salt water?
Engine installation height?
Boat trim angle and balance?
The bottom line is that you will never know the best until you try, and if you have a serious prop supplier he will let you 'try before you buy' to find what suits your needs.
My recommendation was simply by experience as a suggestion to TRY, but decision is yours.
Two people, 'same' boat, 'same' engine often ends up with different props. Might be same 'pitch', but different prop characteristics. Did a test some years ago with two experienced boat journalists.
5,7M Center consol boat, 150 Ficht. They tested both with Raker and 'old' type Viper. Flat water top speed about 1 knot faster with the Raker, but on a 5 N Mile 'course' around some islands, the Viper turned out to be the fastest in total time!!

 

[Theoutdoorsman]

Re: 1989 Evinrude 140 lower unit gear question

Interesting observation indeed. This is a freshwater application, for the record. Cavitation plate is nearly even with the bottom of the boat. I'm not really certain there is anything else I can do short of changing my gear ratio or installing a jack plate. Have you any experience with gear swaps on these older outboards, if it's even possible, or would it even be worth my time and money invested? Many thanks for allowing me to pick your brain ...

 

[Dhadley]

Re: 1989 Evinrude 140 lower unit gear question

Is the motor in your avatar the motor we're talking about?

 

[emoney]

Re: 1989 Evinrude 140 lower unit gear question

Man I miss my old 'Rude 140. You know the old saying...."If it ain't broke, keep trying and it will be", lol. Sounds like she's doing a great job for you as she is.

 

[Haffiman]

Re: 1989 Evinrude 140 lower unit gear question

It is possible to install the V6 gears, but again you will end up with having to change prop!! Depending on the angle of the V of the bottom, (No pad), the cav plate ought to be somewhere between 1/2"(10 degr) to 2"(30 degr) above bottom. It is even depending on type of prop used. A trial and fail (succeed?) procedure to find the right position.

 

[Theoutdoorsman]

Re: 1989 Evinrude 140 lower unit gear question

Is the motor in your avatar the motor we're talking about?

Yes, Dhadley, it sure is! And, as a matter of fact, you helped walk me through a complete powerhead rebuild on it nearly five years ago. Thank you again! Checked compression on her just yesterday and all is still well today. Over 90 psi on all four holes and within 10% of one another still.... .... By the way, this is a 1979 Evinrude 140 ...... NOT ...... '89. I must have hit the wrong key by mistake. Sorry.... ;-)

It is possible to install the V6 gears, but again you will end up with having to change prop!!

1.) Changing the prop is something I had already expected I'll have to do anyhow. This, I already understand. Considering the monetary difference beween adding a jackplate vs. gear swap is beyond my scope of knowledge. So far as I can see, these are the only two options I have ....... correct?

2.) I am certain I could pick up a used 6" manual jackplate for around $150-$200. What I'm not sure of is, will I also need to purchase shift and throttle cables as well?

3.) When the value of these cables is included in the total cost to install the jackplate, will I have spent more than I would had I considered the lower unit/gear swap instead?

4.) What pro's and con's are involved in the lower unit gear swap?

This is my delima. Sorry for all the questions. I realize they must seem rather silly to you. If there are other options I am unaware of, by all means I'd love to hear them. Thanks. I'll check the exact cavitation plate height and get back with you on it.