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Need #8 (7.9 x 7.9) prop for 6hp Nissan outboard, sources?

D

dmede

New member
I have a 2002 NSF 4A2 (or NSR 4A2D per the motor plate) Nissan outboard. I replaced the original carb with the 6hp carb, basically converting the motor from 4hp to 6hp. I want to swap the prop to match and get as much extra speed out of the HP gain as possible (even 1-2 mph more would be great). I have a #7 on there now, which I think makes it a 7.9 x 7.0 (dia x pitch). I think the 6hp would have been a #8 (7.9x7.9).

Anybody here know where to search online for a #8 that will fit my motor? Possibly a source for used? My searches seem to come up with only newer motor parts. Also, is the spline universal, will any 7.9 x 7.9 fit my outboard?

Thanks,
David
 
Any prop for any 4/5/6 4-stroke will fit the prop shaft splines. 5 props are available: 6-pitch (393B645121), 7-pitch (3R1B645141), 8-pitch (3R1B645161), 9-pitch (369B645181) "standard" props, plus the 6-pitch (399B645121) "mouse-ear" high thrust prop. MSRP is $70.96 for any of the standard props, $78.61 for the HT prop. These are available from any dealer, including me.

What is your current WOT RPM? Increasing pitch may not be what you need for more speed, if you are just plain under-powered. In some cases (heavy boats, for example), using the HT prop helps a lot.
 
Thanks Paul, I wasn't sure if prop splines were brand specific so that's good to know since I think I was coming up with "out of stock" when searching for the OEM replacement on your site.

I don't know my RPMs at WOT, no tach. Power is ok for my type of boat. Like I said above the original motor was the Nissan 4hp. I replaced the carb (ordered from here I think), with the 6hp model carb which is the only real difference between the two models... besides the install prop (4hp has the 7 pitch 6hp has the 8 pitch). My only thought here is to now math the prop to the slightly increased HP and RPMs on my outboard to get little more speed. I know it may seem trivial to focus on such a small diff in prop size but this motor is the largest I can get on my transom due to weight so maxing its potential speed is important. The boat is an older wood design with a full mid section but narrow aft, like a rowboat. It means good carrying capacity but can only handle up to I think 60lbs of motor.

DSC_0475.JPG
 
David,

Outboards and props are indeed brand-specific. But... All Tohatsu/Nissan 4/5/6 4-stroke props interchange. That holds true for the old 2-stroke 5 hp motor, and the newer Merc 4-strokes, as well as the 2012 Evinrudes.

In your case, you are definitely a little under-powered. (Maybe that big fish is slowing you down:) )

I have a similar situation on my sailboat... My rig is 8,000 pounds, and calls for a 15 hp motor, but it won't fit the boat well, so I am running the 9.8, but have installed the "trick prop" for the 9.8, which is a high-thrust prop. My top speed is about the same, but acceleration and handling is much better with the HT prop, especially in reverse.

In your case, it is doubtful that any standard prop will get your motor to the full WOT RPM. The motor is just a little small for the displacement load. That said, it may give you a little more top speed (at a possible loss of acceleration) if you go with the 8 pitch. It's still trial-and-error, so YMMV. Since it's a good idea to have a spare prop anyway, it would make sense to have 2 different pitches... Then you can compare results. The question now is whether to go with the steeper pitch, or the "mouse ear" prop, which has a lot more swept area (much larger blades), for more thrust. There is a distinct possibility that the HT mouse ear prop is what you want, since it behaves like a much steeper pitch, since it "shovels" more water per revolution.

If it were my rig, I'd try the HT prop. You can drop me an email at the office: [email protected], or call 716-877-8221 and either Charlie or I can help you.
 
pvanv said:
David,

Outboards and props are indeed brand-specific. But... All Tohatsu/Nissan 4/5/6 4-stroke props interchange. That holds true for the old 2-stroke 5 hp motor, and the newer Merc 4-strokes, as well as the 2012 Evinrudes.

In your case, you are definitely a little under-powered. (Maybe that big fish is slowing you down:) )

I have a similar situation on my sailboat... My rig is 8,000 pounds, and calls for a 15 hp motor, but it won't fit the boat well, so I am running the 9.8, but have installed the "trick prop" for the 9.8, which is a high-thrust prop. My top speed is about the same, but acceleration and handling is much better with the HT prop, especially in reverse.

In your case, it is doubtful that any standard prop will get your motor to the full WOT RPM. The motor is just a little small for the displacement load. That said, it may give you a little more top speed (at a possible loss of acceleration) if you go with the 8 pitch. It's still trial-and-error, so YMMV. Since it's a good idea to have a spare prop anyway, it would make sense to have 2 different pitches... Then you can compare results. The question now is whether to go with the steeper pitch, or the "mouse ear" prop, which has a lot more swept area (much larger blades), for more thrust. There is a distinct possibility that the HT mouse ear prop is what you want, since it behaves like a much steeper pitch, since it "shovels" more water per revolution.

If it were my rig, I'd try the HT prop. You can drop me an email at the office: [email protected], or call 716-877-8221 and either Charlie or I can help you.
Click to expand...

Thanks again Paul,

I think what I need to do now is take the boat out and test my current setup again, paying attention to hole-shot speed and top end speed. I've done this before and my impression in using the boat with light and moderate loads is that it has all the initial acceleration I need, but not enough top speed. From my understanding that suggests steeper pitch. Plus, again, I'm really just getting back to stock in a sense since I have the stock 4hp prop on what is now a 6hp motor. I'll check and get back t you directly to order later. It may be a few weeks but I'll want this before Sept when I'm taking the boat on a longer weekend trip.
 
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