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1990 Searay 250 Sundancer. 7.4 L, Bravo 1. 4200 rpm WOT 33…

1990 Searay 250 Sundancer...

1990 Searay 250 Sundancer. 7.4 L, Bravo 1. 4200 rpm WOT 33 mphr ?

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I think the boat should have more speed.

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Answered in 1 minute by:
6/21/2018
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,240
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
Verified

Hello my name is ***** ***** am I speaking with? I read what you wrote. Is there any kind of story or history to this boat? Has it ever run any better for you in the past, or did you just buy it and this is the way it is?

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Customer reply replied 2 months ago
Voris here. Just bought the boat.

HI Voris. Mercruiser engines are cataloged by serial number, do you happen to have that number handy so I can look your engine up? How fast do you think or feel this boat should go?

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Customer reply replied 2 months ago
What should the top sped be, what range .. seem to be getting WOT RPM
Customer reply replied 2 months ago
Do not have serial number here. 1990 Mercruiser 7.4 l, carb, bravo 1.
Customer reply replied 2 months ago
I think she should go faster than 33

Ultimately the speed depends on the quality of the propeller. Do you know which size propeller you have on there now? Do you know if it has a cheaper, inexpensive grade of propeller? Or does it have a high performance propeller on it?

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Customer reply replied 2 months ago
I know the prop is the issue to a great extent, my question is what speed would you be looking for? I will know the prop details this weekend ... simple question ... do you feel it should go faster than 33 at 4200 rpm ?

I have boat propeller calculation software that I can use to calculate the approximate speed of the boat. But in order to do that I need to know the engines horsepower output. Those 454's were made in a bunch of different horsepower configurations. The lowest of the 454's were 310 horsepower. The highest were closer to 400 horsepower. That is why I had asked for the serial number of the engine. If I had that I could run it and see what the horsepower was, run the calculation software, and see what it should have for a propeller and see what it should be getting for speed. But I need more information from you in order to do that. There are no time limits here, can you get back to me this weekend with both your engine serial number information as well as if possible, the current propeller size?

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Customer reply replied 2 months ago
The engine is a 330 hp. Stainless steel prop ... can we get some feel for a top end speed ... give me the assumptions you make and then I can see how they fair woth the actual data ?

Give me a few to play with the prop calculator and see what I get.

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Customer reply replied 2 months ago
OK. thanks. If the 33 mphr is in line ... OK ... if not I want to look at it more. I am 62 years old. Not looking for high speed or fast get out of the hole ...... more for overall cruising and fuel efficiency. Trimming her with tabs I can get about 19 mph at 3100 rpm on plane. Runs at 23 -24 at 3500 rpm. She does burn oil at 3500 continuous, another issue.

Are you at high altitude or sea level? (It does make a difference)

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Customer reply replied 2 months ago
sea level, Chesapeake Bay

Got it. I ran the prop calculation software. It came back and is saying a Mercury Mirage prop, sized 15.25 Diameter X 19 pitch is the optimal size for that boat. I am getting an estimated engine RPM of 4400 and an estimated top speed of 47 MPH. This calculator is not perfect, but it's usually within 10 to 15% (either way) 95% of the time. I could increase those odds to 100% if I had the engine serial, gear ratio on the sterndrive, and current propeller size. But 47 MPH does sound closer to what it should be to me. I do want to make sure you are happy with my service before you go. If you had a further or more specific question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

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Customer reply replied 2 months ago
33 mph on the new GPS with the stainless prop and 4200 rpm sounds like a problem ...... compression was tested after running her for 30 minutes in April .. tested at 133 -- 145 lbs. Thoughts ? could the different prop make that much of a difference if the existing is far off in dia and pitch ?
Customer reply replied 2 months ago
I'll certainly give you a good rating.

The compression numbers are fine. Did you get my previous response where I covered top size and estimated top speed?

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Customer reply replied 2 months ago
I saw the recommendation for the Mirage 15.2 by 19, 45 mph. My question is can do you feel an existing sstl prop could be performing so poorly ?

Yes definitely. I have no idea who makes the prop, and I have no idea what size it is. Just like tires, there are vast quality differences in propellers. A cheap propeller just won't perform high a good propeller will, regardless of if it is stainless steel or aluminum. For example, A company called "Michigan Wheel" makes cheap, inexpensive, stainless steel props, and they perform horribly especially next to a Mercury propeller of the same size.

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Customer reply replied 2 months ago
OK, thanks. I have a lunch appointment. I'll send the positive response after that. thanks

You are very welcome and I was glad to help. Please do not forget to select that 5 star rating for my service. Thanks again and good luck! -Jason

Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,240
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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