Correct prop for a Mercruiser 120

[highfigh]

Working on an '84 Four Winns Marquise 170 and it came with one dinged up 48-78118-17 and one dinged up 48-78116-15- the first is a 15-1/4" x 17 and the second is 14-1/2 x 15. Knowing this isn't going to shove me back into the seat but I wouldn't mind of it can get out of its own way, which prop is going to be most practical and provide the best performance? I doubt I'll be slow-trolling, so I'm guessing the 17" pitch will be good but since I haven't put the boat in the water yet, I don't know how it will perform without bogging. I know the 17" will chop off the top end RPM and I don't really need to run it at WOT.

Any first hand opinions or info for the OEM prop match?

Thanks, in advance.

 

[QBhoy]

Working on an '84 Four Winns Marquise 170 and it came with one dinged up 48-78118-17 and one dinged up 48-78116-15- the first is a 15-1/4" x 17 and the second is 14-1/2 x 15. Knowing this isn't going to shove me back into the seat but I wouldn't mind of it can get out of its own way, which prop is going to be most practical and provide the best performance? I doubt I'll be slow-trolling, so I'm guessing the 17" pitch will be good but since I haven't put the boat in the water yet, I don't know how it will perform without bogging. I know the 17" will chop off the top end RPM and I don't really need to run it at WOT.

Any first hand opinions or info for the OEM prop match?

Thanks, in advance.

I think there is no doubt that you’d learn lots from trying what you have. I’d start with the 17”…if all is well and healthy otherwise and elsewhere.
But I would also suggest that the 17” you have has a huge diameter and would not usually be found on such a set up. A black max 17 these days would have a little less diameter than that, I’m sure.
See how she goes but be aware of having quite a large diameter having at least a little affect on things perhaps.

 

[Scott Danforth]

I had a 15p, 17p and 19p in my 3.0 powered boat and had to swap props often. Your down 20hp from where I was. You may be running the 15p

 

[Bondo]

Working on an '84 Four Winns Marquise 170 and it came with one dinged up 48-78118-17 and one dinged up 48-78116-15- the first is a 15-1/4" x 17 and the second is 14-1/2 x 15. Knowing this isn't going to shove me back into the seat but I wouldn't mind of it can get out of its own way, which prop is going to be most practical and provide the best performance? I doubt I'll be slow-trolling, so I'm guessing the 17" pitch will be good but since I haven't put the boat in the water yet, I don't know how it will perform without bogging. I know the 17" will chop off the top end RPM and I don't really need to run it at WOT.

Any first hand opinions or info for the OEM prop match?

Thanks, in advance.

Ayuh,.... The "Right" prop is the one that will allow yer motor to rev to 4400/ 4600 rpms, at Wot,......
Any less than that is luggin' the motor, at All rpms, which causes detonation, which burns holes in pistons,.....

 

[j cat]

Working on an '84 Four Winns Marquise 170 and it came with one dinged up 48-78118-17 and one dinged up 48-78116-15- the first is a 15-1/4" x 17 and the second is 14-1/2 x 15. Knowing this isn't going to shove me back into the seat but I wouldn't mind of it can get out of its own way, which prop is going to be most practical and provide the best performance? I doubt I'll be slow-trolling, so I'm guessing the 17" pitch will be good but since I haven't put the boat in the water yet, I don't know how it will perform without bogging. I know the 17" will chop off the top end RPM and I don't really need to run it at WOT.

Any first hand opinions or info for the OEM prop match?

Thanks, in advance.

15-1/4 dia X 17 pitch the engine rpm is 3900-4300 RPM max throttle ..
is your prior prop the engine RPM over the spec RPM ?

 

[Bikestdy]

I have a '85 170 Horizon with a Merc 470 (170hp). I run a Turning Point 4bl 17p and that puts me a bit over max rpm but use it for the hole shot power for water sports. A 19p puts me in the the correct rpm range.

For general all around try the 17p, the 15 is probably for water sports.

 

[highfigh]

15-1/4 dia X 17 pitch the engine rpm is 3900-4300 RPM max throttle ..
is your prior prop the engine RPM over the spec RPM ?

The boat owner has two props, both from Mercruiser/Quicksilver with 48-xxxxxx numbers and I have no reason to believe that anyone actually knew what to use, considering the general care given to the boat in the past.

 

[Scott Danforth]

The boat owner has two props, both from Mercruiser/Quicksilver with 48-xxxxxx numbers and I have no reason to believe that anyone actually knew what to use, considering the general care given to the boat in the past.

its very common to have 2 or 3 props for a 4-cylinder powered boat mainly because you are limited on power.