Mercury Remanufacturing 383 Magnum and Sundancer 290

S

SteveMoffat

New Member
Dec 4, 2007
13
Bermuda
Hi folks

I have a 1992 Sundancer 290, single 7.4L and Bravo One Sterndrive.

I have been given, (yup, freebie), a brand new, still on the pallet, 383 Magnum.

Now, knowing that I will have to change the gearing on the sterndrive, which is OK, has anyone fitted one of these engines to a 29 / 30 footer and if so what ratios dod you end up using in the drive??

I live in Bermuda and if I don't get this right first or second time it'll cost me a fortune....:(

Thanks

Steve
 
What's wrong with your current engine? How many hours does it have on it? Might you be better off swapping your MOPAR 383 Magnum for a rebuilt 7.4?
 
That would cost a small fortune in Bermuda with 55% import duty and shipping costs. Roughly about 10k as opposed to nothing....

Plus the magnum is a better engine. Fresh water cooled, ECM etc. The old engine is from 1992..god knows how many hours are on it.
 
I was considering that engine for my boat because of the excellent price, but I just didn't feel the small block would have enough torque. I certainly wouldn't consider it without a Bravo 3, and probably not at all on a 29. What does your boat weigh?
 
The 7.4 is a great match for your boat...lots of torque. Mine runs strong and has good compression on all cylinders. Not sure about the 383 mag ...just had to post since we have the same boat !
 
I have the 383 mag and bravo lll in my 87 250 da and I couldnt be happier. I have A freind with A 87 250 da with the 454 bravo l and my boat will blow his away and burn half the fuel he does. I think my boat is much lighter than yours so I dont know how it would do in your boat.
 
Thanks tmsrb that's good to hear. How does it compare heavily loaded?? I hope to someday repower with a 8.1/375 HP minimum.

I guess I also always believed that a larger engine working less would offer better fuel consumption that a smaller engine working harder in the same boat...

For example say a 60mph Stingray 220 with a 5.7 will get 6 mpg at 2500 RPM/25 mph. Would the 3.0 be able to do the same???

SteveMoffat said:
I have no idea.
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Dry weight on your boat is 5800 lbs. - only 280 lbs. more than my boat. It may actually perform more efficiently with the lighter hull loading. Considering it was free and where you are located you almost have to give it a try. Let us know how it works out!!!
 
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tmsrb said:
I have the 383 mag and bravo lll in my 87 250 da and I couldnt be happier. I have A freind with A 87 250 da with the 454 bravo l and my boat will blow his away and burn half the fuel he does. I think my boat is much lighter than yours so I dont know how it would do in your boat.
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he needs to get his tuned and figure how to prop it. something is wrong.
that 383 stroked small block is a great engine but its not a match for the torque of that big block if its running right
 
My boat will run 48 mph "gps" 3600' elevation with 4 people full of water and at least 80 gal. of gas. I have 26 pitch props on it. It burns 7 gph at 3500 rpm and 31 mph.

Last week I had 100 gal. of gas full water about 1120 lbs of people and got on plane with no problem.
 
Also a '92 290DA owner, I would think going up to a 496/8.1 would be the best idea.

I saw the Mercruiser repower guide online, and no where did I read that it was a direct replacement. Sure, it has 320hp compared with the stock 7.4 at 300hp...

But what about torque?

You need big cubes for that, especially in a big, heavy boat.

But, to answer your question...these days, boats this size (28-29') have an 8.1 or more often, twin 4.3s/5.0s.

I'd look at what ratio a 25-26' cruiser (at as comparable weight as possible) uses and go with that.

My guess is that the 290 is much heavier than today's mid 20 foot cruisers and you may be disappointed with the performance. Then what?
 
Quote from the merc website.

The remanufactured 383 Magnum multi-port fuel injected power-plant is based on a small-block 6.2-litre engine, but features a larger-bore-diameter and longer stroke that provides 325 “propshaft” horsepower with tons of torque. This is a perfect, economical replacement for the no longer made 454 and 7.4 engines that were previously popular.

S
 
Just a quick update. Finally had the engine and outdrive fitted last wek. Boat was put in the water Friday. WOW. That's all I can say. 37MPH. The 7.4 did 28. It's a lot quieter, much much better on gas, 12 hours so far at varying revs and still have more than half a tank of gas. Old engine would have required a trip or two to the gas station.

I am very happy with it and would recommend it to anyone needing to replace a 7.4.

S
 
SteveMoffat said:
Just a quick update. Finally had the engine and outdrive fitted last wek. Boat was put in the water Friday. WOW. That's all I can say. 37MPH. The 7.4 did 28. It's a lot quieter, much much better on gas, 12 hours so far at varying revs and still have more than half a tank of gas. Old engine would have required a trip or two to the gas station.

I am very happy with it and would recommend it to anyone needing to replace a 7.4.

S
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Did you end up putting the 383 in your boat?
 
I wonder if I have room for 2 of these in my 280? From what I hear these 383 are unreal. If they'd fit I could probably cruise at 3000rpm/30 mph burning equal to less than my 4.3's. Then I could throttle up and do in the 50's!
 
First of all know the differences. Your 1992 290DA is much heavier than the 268Sundancer (which many love to call 29 footer) The 383 may work but I would take time to compare some things such as the HP rating @ what RPM, the torque rating and keep in mind that a 7.4L Base engine is not a direct comparison to a 383 cid Magnum. The bore and stroke are different and an experienced mechanic can explain that to you.
Last summer I nearly purchased a 290 but it needed repower. Previous owner was HP hungry and changed the orig 7.4L base to a 502 CID. Alot more power but the 502 is known to be a rough runnign engine due to the large bore of the 8 cylinder block. Had I purchased the boat, I would have gone with the 8.1L Horizon (496CID) and nearly the same engine mounting locations and more similarity to the orig 7.4L. The 8.1L has varied V degrees for each pair of opposing cylinders. It is one of Mercruisers pride engines for smooth operation. I may not have given you the answer you are looking for about the 383, all I say is take time to know the differences.
 
srt8mag said:
I wonder if I have room for 2 of these in my 280? From what I hear these 383 are unreal. If they'd fit I could probably cruise at 3000rpm/30 mph burning equal to less than my 4.3's. Then I could throttle up and do in the 50's!
Click to expand...

The answer is yes it will fit. The 383 is 5.7 (350) block with longer stroke.
 
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