Mercruiser 357 Reman Bravo 4V

[searaypassion17]

Hello, I am looking for some insight/opinions on a engine swap that I am doing in my 1999 Searay Sundancer 270. Originally the boat has a 7.4MPI L29 engine 310HP and the boat would get up and go near 40MPH if I really pushed it. Now I had to replace it because it started knocking. I already purchased a 357 re manufactured engine from mercruiser that is 325 HP. My concern is if the new engine will be enough for my size boat since I went from a big block to a small block. Mercruiser says it replaces the 7.4l but I am not to sure on how well it would work with my boat since it is not as torque as my old engine. I believe the boat weighs around 9000 pounds and it is powered by a Bravo III dual 22p 3 blade props with a 2.20 gear ration. What are your guys opinions. Will the engine provide enough power and torque to get up on plane with lets say 5 passengers? TIA

 

[Scott Danforth]

welcome aboard

the L29 big block had 380 hp at the crank (rated at 310 at the prop - however closer to 330)

the 357 is 325hp rated at the crank. so your down 55hp to about 260-270 at the prop.

I would have rebuilt the L29 with a scat stroker kit and changed cams to get 450 at the crank with the L29. you could have rebuilt for about $2500 or less

 

[Scott06]

Here's a repower article with a 383 similar size . You may have wanted a 383 vs 357, but really matters how you use your boat. If you can pitch down in prop probably ok, you'll loose some top end but prob doesn't matter

 

[alldodge]

Don't think your 270 weight is 9000, the searay is a light boat and more along the line of 7800 dry

History of 454 and 7.4

7.4 and 454 motors
carb was 300 hp
carb HO was 350
mpi 310 L29
mpi LX 330
mpi HO Mag 385

The L29 has the throttle body in the middle of the motor, all others have the TB at the front end of the plenum

The 357 is a bored out 350 and while I do think it will be sort of OK, it does not have the low end torque. The torque is what you need to get the boat up. Rebuild what you have an pull some more hp from it and you will be real happy.

If you want to be elated, replace the 454 with a 502 and she will do better then you ever thought

 

[Scott Danforth]

When rebuilding a gen 6, L29 a SCAT stroker rotating assembly would make it a 496 (8.1 liter)

Its cheaper than reconditioning current crank and rods and getting new pistons and rings

my guess if its knocking, rod bearings 3 and 4 went

 

[searaypassion17]

Don't think your 270 weight is 9000, the searay is a light boat and more along the line of 7800 dry

History of 454 and 7.4


The 357 is a bored out 350 and while I do think it will be sort of OK, it does not have the low end torque. The torque is what you need to get the boat up. Rebuild what you have an pull some more hp from it and you will be real happy.

If you want to be elated, replace the 454 with a 502 and she will do better then you ever thought

It’s a big boat . 9 foot 2 inch beam with ac unit. But I’m not 100% sure on it’s weight. Unfortunately I sold the old engine and it had problems with the ecm , can’t get a new computer for that engine.

 

[searaypassion17]

Here's a repower article with a 383 similar size . You may have wanted a 383 vs 357, but really matters how you use your boat. If you can pitch down in prop probably ok, you'll loose some top end but prob doesn't matter

I am in a budget and was lucky enough to pay dealer price for this new engine with extended warranty. The 383 was way out of my price range. But I can play around with different pitch or even gear ratio change if need be

 

[Scott Danforth]

if you were dealing with a budget, rebuilding what you had would have been the most frugal route. that big of a boat with the small block, you simply wont be happy with it. While Searay Sundancers came with the 350 mag /Bravo package, they were not stellar performers