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Old 08-11-2019, 06:30 AM   #1
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Default 4600 plane speed and RPM with 450C engines

I have looked at speed and fuel burn rates for the 4600 from several post, but am wondering what others are experiencing to get up on plane and stay there. My personal experience is nowhere near the graphs I have seen.
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Old 08-11-2019, 04:27 PM   #2
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I have an 01 with the 450s. I easily get up on plane in less than 10 sec. We cruise around 2250 (19kts) and at that speed burn about .9 - 1 gallon per NM. Only changes we plan to make in the future are 5 port versus 4 port injectors and 180 degree thermostats. I've read that should reduce some of the soot the motors generate. When I did the valve lash at 1000hrs that also helped reduce soot.
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Old 08-12-2019, 12:23 AM   #3
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I also have a 46, with 450’s and the hard top. I agree with Steve’s numbers, and am appreciate the tips to reduce soot. We are at 650 hrs.
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Old 08-12-2019, 04:26 AM   #4
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Thanks for the replies. Next time I am out I will check again on my plane speed and rpm. It might be a little different as I have a fairly heavy tender hanging off the back.

SteveP - To get on plane do you go WOT and then back off, or just set to 2250 to get on plane?

As for soot, a previous owner put the 5 port injectors in and i put in the 180 degree thermostats. Overall not too sooty, but I do get a decent amount of white smoke at start up. I added oil pan heaters and I think they helped a little, but I probably need to have the valves and injectors checked out.
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Old 08-12-2019, 05:23 PM   #5
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I generally move my throttles firmly but not too fast up to about 23-2400. I'll then back off a bit as things stabilize. I also have boost/egt and it seems the egt is about 20 degrees lower if I'm trimmed a bit nose down.
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Old 08-12-2019, 09:19 PM   #6
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I have a Nouvara dinghy with a 25 Yamaha on Olsen davits on the back. WOT is 2400 rpm/22 kts. It planes out at 2200, then I pull it back to 2000/17-18 knots.
I will be cleaning/tuning my injectors this fall and will inquire about 5 Port options.
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Old 08-13-2019, 01:18 PM   #7
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If you can only make 2400 at WOT you may be over propped. Search on the following 2 web sites and you'll get a lot of advice about reducing pitch on your props so the motors can achieve 2600+. The other item mentioned often is cleaning your aftercoolers.

www.boatdiesel.com & www.sbmar.com
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Old 08-13-2019, 08:53 PM   #8
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Yeah my mechanic and I are investigating this. Thanks for the additional info.
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