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My Whaler is the "big" Montauk-- the 190. The engine is a 115 e-tec; and its full throttle RPM range should be 5,500-6,000. I upgraded from an aluminum 14.5 x 19" pitch, to a VIPER SST 14.75" x 19" pitch.

This was upon advice that I should make a same pitch conversion if I was happy with the original Aluminum; and especially if the rig is a light, stripped down boat with no excess of weight loading huge center consules, chairs, rocket launchers, no skiing, and very few times being used other than solo. This was bad advice.

The engine turns only 5,100 RPM at full throttle. I am definitely over pitched.

So now I have to humbly go back to my boatyard, and ask them to swap down. My choices in the VIPER propeller product line are 14.75 x 18, or a 14.75 x 17" pitch.

Which pitch choice do you think I should run with to get another 500 to 600 hundred RPM-- to bring engine full throttle RPM output up to 5,600 to 5,700?


Thank You,

SK

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To make sure you get the best performance, at what position is the engine mounted?

Counting down from the top, what holes are the top set of bolts?

Top set of holes:

O
O
O
O

I recall that an E-TEC likes to be high, like in the 3rd of 4th hole.

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Mounted in the 3rd hole set from the top. I definitely have the engine up high. In fact. I had the yrd move it up to this notch two years ago because I didn't like where they put it.

SK

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That motor should go up as high as possible. Before testing anymore props, move it up that last bolt hole (3/4") and retest the Viper.

Dropping to an 17" Viper will bring your RPM up to 5400-5500 RPM but raising it that last bolt hole will gain you another 100-200 RPM by itself.

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SK,
Just had the same problem with my switch from a 12.7 x 19 - 4 blade Comp prop to a 13 x 19 - 4 blade Rogue stainless on my 2010 90 HP E-Tec on the 16SL.

The slightly smaller Comp prop turned up 5,400 rpm and the stainless hardly reaches 4,800 rpm. The difference in hole shot is amazing. Comp prop jumps out of the hole and stainless is like pulling three skiers???

Going to try a 13 x 17 - 4 blade stainless but have a feeling the Comp prop will end up the best overall performer.

Good luck with your testing and next prop.

Jon B.

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Jon -

Let's stick to the same engine size/prop subject in this thread.

Most ETEC 90 hp owners are running a prop recommended by our "prop guru", Tom that is listed in this thread.

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Thank you for these replies. Tom: I had no idea raising the engine could deliver more prop RPM. However, I am hands-on certain I should not raise this engine higher. We do a lot of heavy weather and seas boating here on Cape Cod; and the engine configuration height I presently have is already aggressive and prone to cavitate coming off a wave. The favorable trade off is that I did gain about 2.5 mph top end in calm water conditions when I notched the engine up last season.

Subsequently, I talked with a local business, called NEW ENGLAND PROPELLER INC., and they are adamant that a SST conversion from an adequate Aluminum prop-- you need to drop down TWO pitch sizes. So, the next prop I'm going to try to grab off the shelf will be the VIPER 14.75 X 17, I guess.

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You may find that a 15" Rebel prop will give better cruising performance and fuel economy than the 17" Viper and about the same rpm. You do need to get those WOT rpms up in the 5600 rpm range or better.

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Moderator Phil T. - I understand your concern about the "same engine/prop subject" and hijacking the thread ................however with all due respect; the actual point I am making.....is on the recommendation SK was given to make a "same pitch conversion".

The actual change from aluminum (or composite in my case) to stainless was NOT a "same pitch conversion" for me either.

The purpose of my post was to hopefully save other site members from the same issue both SK and I had with our same pitch conversion to stainless props, regardless of what engine/prop size you have.

Respectfully, Jon B.

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SK, your shop is applying a rule of thumb, which is not necessarily a bad idea, but you need to be careful of of overgeneralizing. Not all aluminum props are alike, and not all stainless steel (I assume that's what you mean by SST) props are alike either. The original OMC SST prop, for example, was stainless but not highly cupped, so it more or less swapped straight up with aluminum.

In general (more rules of thumb here) an inch of pitch will change your WOT RPM by ~200, and cupping will act like an inch to an inch and a half of pitch - the actual amount depends on the amount of cup, of course. So assuming your old aluminum prop was uncupped, by going to a modern, cupped prop and staying at the same pitch, you effectively increased the pitch, resulting in your low WOT RPM.

I do think the 17 pitch Viper would be good to try, but if it were me, I might start with a 16 if they make one. You have a relatively big boat with a relatively small motor, so unless you're a speed demon, you may want the extra grunt for the times when you're running with a boatful of folks. I'm sure the eTec has a rev limiter, so although you may give up a knot or two, you're not going to hurt anything on occasions when you're running light and fast

Tim