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Thread: Merc 300R Fuel Consumption
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10-27-2022, 11:28 AM #16
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10-27-2022, 03:54 PM #17Team Member
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If I ever get the antenna to work, my Merc Monitor (smartcraft) will show mpg
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10-28-2022, 02:24 PM #185000 RPM
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Hi!
My boat is approx 1350 kg with me in it. Around 2970 lbs. When I had a 400R my milage at 48 mph was 4,36 MPG. My milage with the 450R at the same speed is approx 4,1 MPG. However, I prefer to run 3500, so then I get 4,12 MPG. Max torque is at 4,250, so the engines likes to get up there .. I used a single Promix 300X back in time..... That one swallowed fuel ... !
Cheeers Toffen
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10-28-2022, 11:16 PM #195000 RPM
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I read your post, and I know that the ASC function on my 300R will not allow the rpm to increase if I trim up, but always keep the rpm constant at any rpm below WOT. At WOT the ASC does not operate, so trimming out at WOT will result in more rpm and speed. So I ran mine up to 4000 rpm today, trimmed fully in, and it was pulling around 11.8 gph and running at 40 mph. I then trimmed it out to about half way, and the rpm stayed at 4000 rpm and of course the speed stayed at 40 mph because the rpm did not change. The fuel flow dropped to around 9.1 gph, which makes sense and means the additional trim freed up the hull and it would have run more mph and more rpm but the PCM closed the throttle blade (even though I never touched the throttle) to maintain 4000 rpm, but since the throttle blade was further closed the pulse width of the injectors was likely less which reduced the fuel flow. So mine appears to operate a bit different than yours, in that my rpm at part throttle (and speed in mph) will not change with additional trim, but the fuel flow will be reduced like yours.
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10-28-2022, 11:32 PM #205000 RPM
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Pulsare- My RPM stays the same when I trim up, but my speed increases a lot at the same rpm's due to less drag.......and fuel burn goes down.
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10-28-2022, 11:35 PM #215000 RPM
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Interesting. Neither my speed or rpm changes when I trim out at part throttle, but the fuel flow decreases. At WOT, both the rpm and speed increase when you trim out. If I raise my jack plate at part throttle, the same thing happens, the rpm and speed stay the same and the fuel flow decreases. At WOT, raising the plate will change the speed and rpm because the ASC is not in effect.
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10-29-2022, 07:51 AM #225000 RPM
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Different boat hull designs I guess. Your prop must be efficient at any trim, so when you trim/jack up it just lessens the load on the motor (drag). I have a 20' Lake+Bay backwater flats boat.
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10-29-2022, 10:01 AM #235000 RPM
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That makes sense to me. Under 35 mph, I have to run full negative trim to keep the boat from porpoising, and the bow is still running very high. After about 40 mph, I can use a little bit of trim. After about 55 - 60 mph it will start to push the bow down and you have to give it trim to raise the bow. If I am cruising say at 3000 rpm / 30 mph and I turn the boat, the rpm will stay constant but then the mph does drop due to the drag and the fact that it lost lift from strakes and hull. I have tried at least 6 different props, and all reacted the same regarding no speed increase with trim when the ASC was active, so I think your theory of the hull design is likely correct.
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