redjmp
Chief Petty Officer
- Joined
- Mar 16, 2005
- Messages
- 536
I am trying to determine the correct prop for my I6 merc.
It spins 5800 with what I think is a 17 pitch @ 43 mph.
When I look at the prop selector here at iBoats, It says that the correct rpm range for all years of I6 115's is 4750 to 5250.
The 135 - 150's are listed here as 5000 to 5600.
Now I thought that my 115 is the same motor as an older 140 or 150, the difference being the low dome pistons and the ignition system.
So I don't know if I should go up to a 19 which should bring down the rpms to around 5400-5500 and speed up to 45mph, or to a 21 which should bring it down around 5000-5100 and speed up to 47mph. Then again it will be a steel prop so the rpm drop will be a little less and I do want the most speed and fuel efficiency. I will swap to my existing prop for pulling/towing.
With the aluminum prop I have now, I tend to run motor around 3500 which is the most fuel effecient at around 5.9 mpg @ 27 mph on my cvx/cobra style 15' skiboat weighing about 1600 fully loaded.
Before you go saying this belongs in the prop forum, my only questions are:
What is indeed the correct WOT range for this motor, and am I safe running at 3500 rpm for extended periods or is that considered "lugging"?
It spins 5800 with what I think is a 17 pitch @ 43 mph.
When I look at the prop selector here at iBoats, It says that the correct rpm range for all years of I6 115's is 4750 to 5250.
The 135 - 150's are listed here as 5000 to 5600.
Now I thought that my 115 is the same motor as an older 140 or 150, the difference being the low dome pistons and the ignition system.
So I don't know if I should go up to a 19 which should bring down the rpms to around 5400-5500 and speed up to 45mph, or to a 21 which should bring it down around 5000-5100 and speed up to 47mph. Then again it will be a steel prop so the rpm drop will be a little less and I do want the most speed and fuel efficiency. I will swap to my existing prop for pulling/towing.
With the aluminum prop I have now, I tend to run motor around 3500 which is the most fuel effecient at around 5.9 mpg @ 27 mph on my cvx/cobra style 15' skiboat weighing about 1600 fully loaded.
Before you go saying this belongs in the prop forum, my only questions are:
What is indeed the correct WOT range for this motor, and am I safe running at 3500 rpm for extended periods or is that considered "lugging"?