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Question in regards to RPM
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lsurebel4
MMT Member
Joined: Fri Sep 18, 2009 9:38 am Posts: 28
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 Question in regards to RPM
Took the boat out for a maiden voyage yesterday.
I am running a 18x44 Go-Devil boat that I raised the transom on and have a 35GTR Gator Tail. Boat ran great.
Boat is much easier to drive around 3000 RPM, way less torque and vibration.
Wide Open the boat turned up 4160 or so RPMs with 3 people, 6 gallons of gas, and a 2 blade prop. Is that the sweet spot?
I think it could be turning too many RPM's. Am I right or wrong on that? Also, motor vibrates quite a bit at that level, would a 3 blade prop help that? Thanks!
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Mon Oct 12, 2009 8:15 am |
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dog walker
MMT Elite Member
Joined: Tue Jan 13, 2009 6:08 pm Posts: 5282 Location: Meraux,La.
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 Re: Question in regards to RPM
If you trim the motor too high your rpm's will increase and your speed will decrease.If you have a gps you can watch your speed and adjust your trim to reach the highest speed.If you keep trimming the motor up past the "sweet spot" you will see your speed drop and rpm's increase.
The torque may be a sloved by moving people and gear around in the boat,shifting the motor,bending the skeg,or a torque tab.
If your rpm's are not over 4200 out of the water you should be ok.
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Mon Oct 12, 2009 8:37 am |
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craig
MMT Elite Member
Joined: Tue Jan 13, 2009 7:53 pm Posts: 7515 Location: Chauvin
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 Re: Question in regards to RPM
Those rpm's are fine. My engine turned 4200-4300 rpms in the water when it was stock. Just don't exceed 4400 are your valves will start to float.
_________________ 1750 GatorTail Extreme/Stage 3 37 GTR HD Procrastination is a lot like masturbation. Sure it sounds great at the time but, in the end your only f--k--g yourself.
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Mon Oct 12, 2009 10:04 am |
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hatchie rat
MMT Pro Member
Joined: Tue Sep 22, 2009 2:29 pm Posts: 61 Location: west tn
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 Re: Question in regards to RPM
ok...this might be a dumb question, and sorry to hyjack your thread, but what do yall mean when yall are talking bout "trimming" the motor? like i said......sorry to get off topic jus tryin to learn a lil sumthin 
_________________ 1542 Landau w/ 20 hp BT Longtail custom dual exaust "Hatchie Bottom" paint job
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Fri Oct 16, 2009 1:53 pm |
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craig
MMT Elite Member
Joined: Tue Jan 13, 2009 7:53 pm Posts: 7515 Location: Chauvin
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 Re: Question in regards to RPM
_________________ 1750 GatorTail Extreme/Stage 3 37 GTR HD Procrastination is a lot like masturbation. Sure it sounds great at the time but, in the end your only f--k--g yourself.
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Fri Oct 16, 2009 1:58 pm |
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earl33
MMT 1000 Club
Joined: Wed Sep 16, 2009 3:47 pm Posts: 2261 Location: West Tennessee
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 Re: Question in regards to RPM
SD motors have a trim like outboard motors (bass boats, ski boats). You can trim it up and down to find the sweet spot depending on load. Its all about feel and sound. You can feel the prop hook and pull and hear the change in RPM's when you find or lose that spot...
_________________ If the Steel aint Flying the Birds aint Dying.... Uncle J 1948 holding a LT Uncle J 1848 w/?
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Fri Oct 16, 2009 2:10 pm |
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hatchie rat
MMT Pro Member
Joined: Tue Sep 22, 2009 2:29 pm Posts: 61 Location: west tn
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 Re: Question in regards to RPM
o ok i gotcha
_________________ 1542 Landau w/ 20 hp BT Longtail custom dual exaust "Hatchie Bottom" paint job
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Fri Oct 16, 2009 2:14 pm |
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