rebuilt 260 hp engine installed in 1972 grew [merc] tried 4 props last being 23 pitch alum rpm 5500 should be max 4800 mechanic suggests 23 pitch ss local propellar guy provided 25 and 27 pitch al and said one will work rpm drop 400 per pitch increase local merc dealer says no use merc al prop over 23 pitch vibration etc may be big damage what do to get rpm down safe limit of 4800 rpm
Hi, my name is Kerry
It is my understanding that rpm changes about 200 rpm per inch of pitch.
2 inches difference is 400 rpm
The 27" pitch is the one I would go for and it should put you right in the ball-park for rpm
If there isn't a larger diameter that will fit, you need to use the 27 pitch prop.
I wonder if you have the right gear ratio, that's a fairly steep prop
Was this originally a 228 hp?
what about vibration concern with alum prop.? merc dealer says merc only make 23 pitch alum/? good ppoint gear ratio but more expensive fix . rebuilt 350? chev earley 90 s
The 27 is pretty steep but you don't have much choice unless you change the upper gear set.
You must have more power than the original engine.
yes mechanic say more power at prop. orig. engine 327 chev 1972 215hp at engine repower guy never raised this as an potential problem. is vibration cocern with alum prop over 23 pitch a dangerous situation to boat & passingers?
No, I've worked on boats with steep props and never noticed anything unusual.
The steeper prop may be less tolerant of damage, ding it and it vibrates but they do work okay.
Less pitch is more efficient but the only way to get enough load would be to change ratios or live with a less efficient prop.
thank you how do i exit? i rate you got the job done
Not sure what your end looks like actually, is there an accept button?
no will shut off computer hope you dont lose credit thanks
There must be something you need to click, I haven't gotten credit.
24 yrs exp. Inboard/Outboard mechanic Mercury/ Mercruiser, Volvo Penta and OMC, Johnson/Evin.