2858 Repower to 383MPI?

[AK Sounder]

I currently have a 496MPI (425 hp) with Bravo 3 (2.2 ratio with 24p props) in my 32ft (stretched deck) 2858. The current motor has a warranty issue I am trying to resolve with the shop to repair it (long story hopefully to be resolved). But a possible suggested option would be to repower to a Merc 383MPI (350hp). I’d like to cruise at 24 kts and around 3500-3800 rpm.

I like that 383 SB is 500 lbs less weight but I am concerned I’d be underpowered with 350hp esp when loaded with family/gear. The work to stretch the hull added about 500 lbs of fiberglass but also added a lot of floatation- I currently don’t need much trim tab to get on step but on the one trip I made with 496 the fuel economy/range was not as good as I hoped it would be (1.1-1.2 Nmi/gal)- although I was varying the RPM a lot to break in the motor).

Im sure others have repowered a 2858/2859 with the 383MPI. Is it adequate power? What is fuel economy?

[AK Sounder]

Thinking more about my questions......can anyone it is Usable torque that I am concerned about.

does anyone have info comparison of 383mpi torque compared to 496 torque at say 3500-4500 rpm? I suspect there is a big difference.

other thoughts ?

[kwb]

I like the 383 but in your case the Big Block is the right choice.

[Rick_Kenyon]

My last boat was a 275 and it had the 5.0mpi, which was supposed to equivalent to the older carbureted 5.7. It was way underpowered. Took a long time to plane with only 2 on board and not much gear. Bayliner never should have put that power combo together But I’m sure they did it to meet a price point. If I had kept the boat I would have repowered with the 383 when it came time but in your case, I’d stay with the larger power train unit. I think the 383 would leave you disappointed compared to what you have now.
gas mileage is slightly better with the 5.0 mpi than a carbed 5.7 which my older boat had, but you may only get .25 to .5 mpg better wIth the mpi. Boats arenot economy vehicles unless maybe you are nuclear powered, perhaps.

[ksanders]

First I’m in Alaska like you.

The 2858 is a very heavy 28’ boat. I think it’s as heavy as the 2859 or even heavier.

I have had a 383 and a 496 in 2859’s. My opinion based on that experience is that the 496 is about the perfect engine for a large heavy boat like the 2858.

The 383 while lighter, did not perform as well as the heavier 496 in the same heavy 2859.

Yes there is a crossover of weight vs power output, but in my opinion the 383 is not on the right side of that crossover.

Stick with the 496 and resolve your warranty issues.

Put another way... If I EVER downsize from my 4788 I WILL be buying a 2859 and putting a 496 or larger engine in it. No questions asked. If money is no object my opinion is the 496 and a B2 outdrive is the perfect combination.

[AK Sounder]

A little google research shows that the 496ho produces about [email protected] vs 400ft-lbs for the 383- that seems like a pretty big step down. Thoughts for others with a 383 in a 2858 or 2859?

[AK Sounder]

Thanks guys- esp Ksanders who has had both motors in a similar boat. I’ll stick with the 496- that is what I was thinking is best for my heavy boat anyway. Much appreciated.

[Jeffw]

First I’m in Alaska like you.

The 2858 is a very heavy 28’ boat. I think it’s as heavy as the 2859 or even heavier.

I have had a 383 and a 496 in 2859’s. My opinion based on that experience is that the 496 is about the perfect engine for a large heavy boat like the 2858.

The 383 while lighter, did not perform as well as the heavier 496 in the same heavy 2859.

Yes there is a crossover of weight vs power output, but in my opinion the 383 is not on the right side of that crossover.

Stick with the 496 and resolve your warranty issues.

Put another way... If I EVER downsize from my 4788 I WILL be buying a 2859 and putting a 496 or larger engine in it. No questions asked. If money is no object my opinion is the 496 and a B2 outdrive is the perfect combination.

I owned both models, had them on the same trailer. If memory serves, the flybridge 2858 was about 500 lbs. heavier than the hardtop 289/2859.

[2850Bounty]

Merc's 383MPI 350hp uses a piston profile that is not best suited for producing torque.








If GM would make a better selection, they would be able to get closer to BB torque.




The other factor is the stroke.
BBC 454 or 496 stroke is 4.000"
SBC 377 or 383 is 3.750"

.250" makes quite a bit of difference.

[AK Sounder]

All good points guys - I hadn’t thought about the stroke length or the piston shape. I’ll be sticking with 496ho.

thanks again.

[aknurse]

The only way you're going to gain any better fuel economy in that big girl is by swapping over to diesel. You definitely don't want to downgrade HP and torque.