4600 plane speed and RPM with 450C engines - Maxum Boat Owners Club

infiniti00 · 08-11-2019, 05:30 AM

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.

SteveP · 08-11-2019, 03:27 PM

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.

Scb46 · 08-11-2019, 11:23 PM

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.

infiniti00 · 08-12-2019, 03:26 AM

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.

SteveP · 08-12-2019, 04:23 PM

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.

Scb46 · 08-12-2019, 08:19 PM

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.

SteveP · 08-13-2019, 12:18 PM

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

Scb46 · 08-13-2019, 07:53 PM

Yeah my mechanic and I are investigating this. Thanks for the additional info.

Gargiulotime · 07-20-2020, 01:23 PM

Do you know what pitch and size prop you have?

Gargiulotime · 07-20-2020, 01:25 PM

Do you happen to know Prop pitch specs?

SteveP · 07-20-2020, 01:53 PM

When I purchased a spare set of props from CJR I asked for the original 24x22 Ultrascrew .75 props. For both sets the pitch is now down to 20.5. That gives me about 2650 WOT.

Gargiulotime · 07-21-2020, 12:14 AM

Thank you

Gargiulotime · 07-21-2020, 02:55 AM

Stevep is that prop size factory that you have now. I seem to only achieve 14 knots at 22-2300 rpm. I haven’t pushed it to limit. Sort of scared. It feels like their is more but?

SteveP · 07-24-2020, 10:40 AM

Other than the pitch reduction the props are OEM for the 4600 with 450 Cummins. You should see a bit better than 14 kts at 22-2300. You should also check your Wide Open Throttle (WOT) RPM. As mentioned before you should see at least 2600 loaded (in gear). If not you should check things like hull bottom (clean, etc) and also what your WOT unloaded (not in gear) is. Read some the information available on Boat Diesel or Seaboard Marine websites. Lots of data about the 450 there.

Gargiulotime · 06-20-2021, 08:29 PM

I pushed it to WOT it was at 2500 rpm if the tach’s are
accurate. Only at 17 knots 1/2 full on fuel little currant and flat!

SteveP · 06-21-2021, 05:07 PM

As mentioned in previous posts you should see at least 2600 RPM (preferably higher). Speed at WOT for me is about 25 KTS. Something is holding your engines back and should be identified before the motors are potentially damaged.

Gargiulotime · 08-22-2021, 02:31 PM

Steve are your engines the mechanical 8.3 Cummins. Or do you have a computer. Somewhere about 2001 or so they installed a few modifications it came to fuel control

Gargiulotime · 08-22-2021, 02:33 PM

What is your speed and rpm as I am trying to achieve good numbers. My fuel burn and rpm per Nautical mile are not what they should be. What year is your boat and motors.

SteveP · 08-22-2021, 03:52 PM

Mine are mechanical 6CTA (8.3L)

SteveP · 08-22-2021, 03:56 PM

Boat is an 01. The motors were manufactured the year prior (2000). I cruise at 2250 and get around 19 KTS.