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Top speed for Johnson V4 140 hp outboard ?

M

Modaddyo

New member
I currently have a 1988 Johnson V4 110 horsepower outboard. It's running on my 1988 18 1/2 foot Alumaweld Super Vee. I'm getting about 45 miles per hour on the water top speed. I just bought a 1988 Johnson V4 140 horsepower outboard to run on my alumaweld Super Vee. Does anyone know approximately what my top speed on the same boat would be running the 140 figuring my 110 Johnson is running at around 45 miles per hour ?
 
faztbullet said:
Maybe 3-4 MPH as your adding about 70LBS to rear and depends on if it has big or small gearcase....
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Really? It weighs 70 lb more?! I'm going to be using the same lower-end. It's extra long shaft. it's hard to believe that I will only be getting 3 or 4 miles an hour faster. That's 30 more horsepower then the 110. I was thinking more like 10 or 15 miles an hour more.
 
Modaddyo said:
Really? It weighs 70 lb more?! I'm going to be using the same lower-end. It's extra long shaft. it's hard to believe that I will only be getting 3 or 4 miles an hour faster. That's 30 more horsepower then the 110. I was thinking more like 10 or 15 miles an hour more.
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Yep, unfortunately speed is a function of RPM, gear ratio, prop pitch, and prop slip. 30HP more will allow you turn a little bigger prop pitch and maintain pretty much the same lower end performance. But, the 140HP and 110HP are both going to max out at 5,500 RPM and with the 2:1 gear ratio those are fixed values. Your only variable is the size (and cupping) of prop you can turn.

Below are some screen shots I took using an online calculator. FaztBullet speaks the truth, you're pretty much looking at a 4MPH gain for each 2" of pitch that you increase. It's just going to be trial an error to find the right prop that works. A cupped prop will act like a slightly larger prop, so if you're in between sizes you can try cupping to find a good middle ground. If you find a larger pitch prop that gives you the speed you want but low end performance suffers you can drill ventilation holes to help hole shot.

19prop.JPG

21prop.JPG

23prop.JPG
 
kevinj said:
Yep, unfortunately speed is a function of RPM, gear ratio, prop pitch, and prop slip. 30HP more will allow you turn a little bigger prop pitch and maintain pretty much the same lower end performance. But, the 140HP and 110HP are both going to max out at 5,500 RPM and with the 2:1 gear ratio those are fixed values. Your only variable is the size (and cupping) of prop you can turn.

Below are some screen shots I took using an online calculator. FaztBullet speaks the truth, you're pretty much looking at a 4MPH gain for each 2" of pitch that you increase. It's just going to be trial an error to find the right prop that works. A cupped prop will act like a slightly larger prop, so if you're in between sizes you can try cupping to find a good middle ground. If you find a larger pitch prop that gives you the speed you want but low end performance suffers you can drill ventilation holes to help hole shot.

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View attachment 18769

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Interesting.. Thank you for the reply and detailed information. I'm learning as I go along with horsepower and prop specifications. I use my boat mainly for fishing. But occasionally I'll use it for my kids to go tubing or skiing. But I'm the kind of guy that also likes to go fast. LOL... So I figured it 140 would pep it up some if I chose to go faster. It's not real necessary. The main reason I got the motor is because it was free. Something about the electronics is not working on it but the rest of it has good compression. I basically have it as a backup motor if my 110 goes out.
 
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