Very Basic Prop Question

J

jamminmaz

Petty Officer 3rd Class
Joined
May 3, 2004
Messages
82
Good afternoon all,<br /><br />So the Lower the pitch number on the prop, the lower the top speed right? If i have a 13-3/4x 15 now, but i want more hole shot for pulling, i just go down to an 11 or maybe a 13, but keep the same diamater right? Its kind of like downshifting to a lower gear in your car right?<br />For a guy that doesn't care about top speed all that much, and wants to be able to pull skiers out quicker, it would probably be worth the loss in top end to have the punch on the bottom right?<br /><br />Thank you
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Very Basic Prop Question

Sounds logical, Maz, but it isn't that simple.<br /><br />Either overpropping your engine (can't reach top of operating rpm range) or underpropping it (over-revs at WOT) can lead to destruction.<br /><br />It is like selecting another gear in your car, but you have to stay there all the time. That can break your car, too.<br /><br />Gonna move this to Outboards
 
W

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: Very Basic Prop Question

jamm, one option may be to drill vent holes in the hub, placed in the correct location, this can add hole-shot and keep your top-end.<br />The main concern would be where you are at wide-open throttle now, RPM-wise.
 
J

jamminmaz

Petty Officer 3rd Class
Joined
May 3, 2004
Messages
82
Re: Very Basic Prop Question

Thanks for the help guys. My tach isnt working (dont know why yet), but if I can figure out the WOT I will let you know. <br />Again, i dont really care about top end all that much, i just like to pull. The other contender is the dang altitude at some of these lakes!!<br />i was at a lake this weekend (which spawned this question) that is 7400 feet high. I the 6% rule is true, my Johnson 100, was making a good 52hp!! This is why i want to prop down to compensate. i guess my other option would be a turbo, but i like the $100 prop idea better.<br /><br />thanks a bunch,<br />jamm
 
W

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: Very Basic Prop Question

You bring another can of worms along if you're opperating at 7400 ft msl...you are running way too rich at that altitude with the factory jets.<br />For every 2000ft above sea-level, you need to lean down one step in jet size (.001) To run correctly at that altitude you would need to go 3 steps leaner with jets, and advance the max timing 2-3 degrees from spec.<br />without changing anything, you would lose about 3% per 1000ft....about 21-22% in this case.<br />If you are traveling to different lakes alot at differing altitudes, jet for the lowest lake you use and prop from there.
 
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