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What Rpms On 502 Mag Wot??

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Old 07-24-2006, 02:40 PM
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Default What Rpms On 502 Mag Wot??

I am trying to get the correct rpms for my boat. Currently running 27 OB 5100lbs 1.81 bravo 3 with 26P props and WOT @ 4600. Shouldn't I be more around 4900-5000? In March (45 F) I was running 57-58, now I am running 52-53 at 4600. Any help much appreciated!
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Old 07-24-2006, 02:53 PM
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Default Re: What Rpms On 502 Mag Wot??

Merc recomended is 5000. Rev limiter is set around 5050.

What RPM were you running in March when the boat ran faster?
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Old 07-24-2006, 03:06 PM
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Default Re: What Rpms On 502 Mag Wot??

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Originally Posted by the duke
Merc recomended is 5000. Rev limiter is set around 5050.

What RPM were you running in March when the boat ran faster?
running 4800 in March, 200 rpms difference due to conditions? Also March water was mirror smooth. Boat runs much better with 1 foot chop.. and still can't get my rpms there under current conditions...
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Old 07-24-2006, 03:17 PM
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Default Re: What Rpms On 502 Mag Wot??

Merc recommends operating rpm of 4600-5000. I try to run mine at 4800-5000. Rev limiter is about 5100 I believe but I've gotten different answers to that question.

Losing 5-6 mph due to temps seems like quite a bit. I seem to lose 1-2 tops when it gets hot/humid.
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Old 07-24-2006, 03:32 PM
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Default Re: What Rpms On 502 Mag Wot??

No, it is quite possible to loose this kind of speed this year. At Havasu they have lost 6-12 MPH and there was thread on this about a week agop. The 502 needs to run at 5000 RPM at WOT to achieve peak HP therefore peak speeds.

Julie
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Old 07-24-2006, 03:43 PM
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Default Re: What Rpms On 502 Mag Wot??

As usual, Julie is right. We just got done running Hugetime1's hydrostream. With the same prop, and same load, we lost SIX mph from running it in May to July. May was light chop, and cool. Now it was hot, VERY humid sticky water. Keep in mind, that the Hydrostream HAS to have bow lift to run, and when we can't get it out of the water because of temps, it slows down.

You are running below where you want to be as far as RPM goes even in March. Julie can tell you where you should be prop wise. I think you are somewhat limited with that Bravo 3, but she is the expert, so I'm not gonna start guessing.
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Old 07-24-2006, 05:46 PM
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Default Re: What Rpms On 502 Mag Wot??

Not doubting you can lose some speed with heat and humidity, but he's in Illinois.
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Old 07-24-2006, 08:52 PM
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Default Re: What Rpms On 502 Mag Wot??

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Originally Posted by noboat
Not doubting you can lose some speed with heat and humidity, but he's in Illinois.
last week was 102 F and 85% humidity. I just figured I wouldn't lose that much though... my merc manual says 2 mph due to conditions...
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Old 07-25-2006, 11:31 AM
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Default Re: What Rpms On 502 Mag Wot??

Quote:
Originally Posted by cherrycobalt262
last week was 102 F and 85% humidity. I just figured I wouldn't lose that much though... my merc manual says 2 mph due to conditions...
Yep, last weekend it was 95* or so with similar humidity here. I lost about 1 mph. It seems like the modified motors putting out more hp lose a lot more. When you lose a certain % then you get out of the power range, then you lose bow lift, then the boat runs wetter, then more drag and even lower rpm, etc, etc. On certain boats it can add up.
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