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Old 09-29-2017, 01:37 AM   #1
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Default recommended cruising rpm

Hey guys, you helped me get all the components up and running. Thanks again. Went on my first three hour cruise yesterday and all went well except I am uncomfortable with how much rpm I had to turn to go 20 mph. I was at 4000. I thought I should be closer to 3300. What can I rely on to not overwork the engine. Not really interested in speed. Want the engine to last. It is an 01 6.2 MPI. The new ones say 3500 is not a problem. Should this be true for my older model. All other things being equal. I forgot to look at the hours. I'll up date.
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Old 09-29-2017, 02:19 AM   #2
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What boat model do you have? What is the WOT? Should be 4400-4800.

I agree you should achieve 20 mph at a lower rpm.

How many people and gear weight do you have onboard?
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Old 09-29-2017, 03:18 AM   #3
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I just purchased an 01 SCR 2900. Had it for 6 month and finally got it in the ocean and just made a three hour trip. I was so proud as it was my first time on the ocean. But I felt like I was have to push the rpm to get anywhere. The new 6.2s indicate sustained 3500 is no problem. I just want to make sure. This trip, I only had two lite people and about 15 gallons of water. Now waste water. And a full fuel load which is supposed to be 103 gallon. Im not to sure of that because I can't find a manual that will tell me for sure.
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Old 09-29-2017, 11:26 AM   #4
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Originally Posted by jtsevier View Post
I just purchased an 01 SCR 2900. Had it for 6 month and finally got it in the ocean and just made a three hour trip. I was so proud as it was my first time on the ocean. But I felt like I was have to push the rpm to get anywhere. The new 6.2s indicate sustained 3500 is no problem. I just want to make sure. This trip, I only had two lite people and about 15 gallons of water. Now waste water. And a full fuel load which is supposed to be 103 gallon. Im not to sure of that because I can't find a manual that will tell me for sure.
The ocean can have strong currents and wave action. If you were motoring against the current that could explain the slower speed at this rpm. How does it perform when on inland water?
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Old 09-29-2017, 02:22 PM   #5
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Is this a single 6.2? or Twins? 4,000rpm sustained should be fine. I could run my 8.1 at around 3,800 to maintain an average of 22-25 kts. Tide current and sea state will have a lot of impact. 3kt tide is common. running wind and a head sea vs. a following sea will also have impact. Running with a tide and following sea vs opposing both can be the difference between 20 - 21 kts and 25-26 kts for the same rpm.

What really matters is where the Max RPM is at Wide Open Throttle (WOT).
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Old 09-30-2017, 07:01 PM   #6
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Thanks again. Not really worried about how fast I go. Just want to make sure I am not over doing the rpm on my single engine 2001 6.2. It is running great, just a little rich, and I don't want to burn it up. Especially not 20 miles out.
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Old 09-30-2017, 07:57 PM   #7
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The sweet spot on my 6.2 is about 3400-3600.
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Old 10-02-2017, 01:01 PM   #8
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01 2900 with a single 6.2?? I didn't even know they made a 2900 in a single. That 6.2 is a re-power. I'm surprised they went with that engine. It has high HP but not the torque of the 8.1.
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Old 10-02-2017, 04:15 PM   #9
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01 2900 with a single 6.2?? I didn't even know they made a 2900 in a single. That 6.2 is a re-power. I'm surprised they went with that engine. It has high HP but not the torque of the 8.1.

Like the 2800 the 2900 was available with a single BBC 7.4 and the 6.2 is being pushed as a common replacement for it but as shrew says it's torque is less. I have read some are happy with the 6.2 and some are not. It is lighter and has higher HP.
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Old 10-05-2017, 03:22 PM   #10
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Your best cruising rpm is at at the speed where the boat is just about to come off plane, but stays up on plane. That's your most fuel-efficient speed.

Like the commenters above noted, you may have been fighting tidal or other currents. I've had situations where my boat dropped from regular cruising speed (~25kn @ 3500rpm) to 16kn with no drop in engine speed or loss of plane because I was motoring into a strong tidal current.

Low speed at high rpm can also mean you have the wrong props or your outdrives may be messed up in some way.
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