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On my Lund boat I used to have a 40 HP 4 stroke Mercury (2001)

and my boat speed was...

On my Lund boat I used to have a 40 HP 4 stroke Mercury (2001) and my boat speed was 31 to 33 mph. With my 40 HP etech (2008), the boat only runs at 25 to 27 mph. The dealer indicated that they optumized the impeller for the recommend RPM. Why is the etech slower?

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7/26/2012

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

Jason, Marine Mechanic

Category: Boat

Satisfied Customers: 25,435

Experience: Degree in Marine Technology. Gas and diesel marine mechanic.

Verified

It really shouldn't be slower, the Etec should be noticably faster. But a couple of quesitons to you, what size boat is this? Are you accurately measuring your speed with a gps unit? And not the dash mounted water pressure driven speedometers (which are notoriously innacurate) And lastly, what is the Etec hitting for rpms, and what prop do you have on there now?

--Jason

Customer reply replied 10 years ago

You made some good points. The 31 to 33 MPH was done with a water pressure speed indicator and the 25 to 28 MPH was done with a GPS. Phyically, I was about a 1 to 2 MPH faster than my brother boat with my 40 HP Mercury but know I'm about 1 to 2 MPH slower than him know. I will have to get back to you on the RPM and prop pitch this weekend.

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

Bill,

Those water pressure gauge speedo's are very inaccurate. When I do speed tests on customers boats for propping purposes, I keep a $100 garmin automotive gps (just an older nuvi) for exactly that reason. When I get out to the boat I turn it on, and then put it in speedometer mode where it shows just the speed and records the top speed, and throw it in my pocket, run the boat, and see what I get according to the GPS.

Now a 3 bladed stainless prop is always going to be your fastest prop. But get me your current props size, and your full rpms, and we will go from there.

Best,

Jason

Customer reply replied 10 years ago

I believe the max RPM of my is 5400 and the prop I have is a 13.75 X 13.

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

You are right there RPM wise, max on the engine is 5500, is your prop stainless or aluminum?

Customer reply replied 10 years ago

It is aluminum.

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

Gotcha,

Now just out of curiosity, do you happen to remember what size prop was on the Merc 40?

Right now I am trying to figure out of the Etec is actually down own power for some reason, or if it is still a prop issue.

Customer reply replied 10 years ago

I do not remenber the Mercury prop size. Would the prop size have an effect on the motor RPM? I also heard that the only difference between the 40, 50 and 60 HP motors Etecs are the carborators or fuel ports. Is that true?

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

Hi Bill,

The key differences between the 40 through 60 is going to be the exhaust tuner (the exhaust pipe in the midsection) diffent injectors, and a diffferent EMM (computer). If your asking if you can turn a 40 into a 60, no not really. It is actually illegal as well. Since the EPA regulates the engines, it would be illegal for a dealer to do the work. If you were going to DIY it, your biggest hurdle would be getting an EMM for a 60. They only come new, you would never find a used one, and the injectors on the engine have to be programmed to the EMM, which means you need all the dealer only software. And a dealer would never do it (again it would be illegal for them).

Now if you don't remember the size of the old merc prop, how long is the boat? And typically, how many people/gear do you put in it at a time?

--Jason

Customer reply replied 10 years ago

It is a Lund Explorer 16'8". It sounds like the only way to improve speed is to go to a SS prop. Would I get the same pitch?

Marine Mechanic: Jason, Marine Mechanic replied 10 years ago

If your after top speed then not necessarily. You actually want to go down on the diameter, and up on the pitch a bit. What I would look at is Evinrudes SSP prop, sized 13.25 X 15. That is going to drop 1/2 in inch and diameter, and up your pitch a bit. That is going to pick you up quite a bit more speed. The part number on the prop is

763950
You can order them from any Evinrude parts dealer.

I do work for tips so I want to make sure you are 100% happy with me before rating me. (obviously it is in my best interest if you are). If you have any further questions on this just fire away.

Best,

Jason

Jason, Marine Mechanic

Category: Boat

Satisfied Customers: 25,435

Experience: Degree in Marine Technology. Gas and diesel marine mechanic.

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