I have a 1986 Galaxie 18ft boat with a xr2 150 black max on it. Motor runs awsome! My question is I top out at 47 mph and cant get more then 5500 rpms. From what i have read I should be pulling 6000 rpms out of this motor. Is this correct? I have no idea what the pitch my prop is (came with the motor) I just know its a 3 blade. The boat is a open bow run about type boat. Can any one tell me what pitch prop they think I shoud be running on this. Im hauling around two adults and two teenagers so there is some weight in the boat. I have attached a pic to give an idea of the size boat.DSC02011-1.jpg
Need more info. 47 is pretty darn fast for a boat that size with that load.
Depends on the motor.Serial# year??Same year as the boat??
Newer motor might have a rev limiter.That what it sounds like to me.
The motor's supposed to max out about 53-5500 rpm's.
You can remove the prop.Somewhere on it's gonna be the part # or the pitch.Stainless or aluminum?
No limiter?Then we need to know the pitch so we can tell you what to use.
But 5500 sounds optimum.More than that and your looking to destroy what you have.
If you have a 21 then you need to go to a 19 to raise the rpm.
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Without the prop size we don't know where to start from.Numbers usually appear near the base of the blades or under the prop nut.
We need to know what size and what material.Also need to confirm the year of the motor.
Is the antivent(cavitation)plate just above the prop about even with the bottom of the boat?
Thanks for the response! I will have more info today. The boat is at my buddies house and will be going there this afternoon. As far as I know its a aluminum prop. I will check pitch and year of motor today. Im not real concerned about the speed. As was stated 47 mph in that boat loaded down impressed the heck out of me. Its just everything I read on 2 strokes say you should be running close to max rpm WOT . That it is best for the motor
At 5500 your not hurting the motor. Granted it is near the bottom of the range but the prop size seems right based on similar applications and speed seems right as well.
According to the info you gave us your setup seems to be working though the slip is at the high end of normal.11%
Is the prop in excellent condition?Does it appear as it may have been on the motor in 86?
If the prop is 26 years old with lots of use it could be worn enough that simply replacing it would help.
Is the antivent(cavitation)plate just above the prop about even with the bottom of the transom?
If the motor is really low simply raising it could gain a couple hundred rpm.
Yes the cavitation plate is about even with the bottom of the transom. The prop looks like its in great shape. Not a nick or bend in it but I really have no idea how old it is. Thanks for all the great info. The motor is very clean and the boat was owned by and older gentleman That didnt use the boat much so it wouldnt suprise me if it was the original prop.