2003 SD 240 Repower Options

E

Evan Mainetti

New Member
Aug 2, 2023
5
Boat Info
2003 240 Sundeck
Engines
305 MPI Bravo III
Hi all! I purchased a project Sundeck 240 with a low-compression 5.0 MPI motor over the summer but am now facing a difficult decision on which engine to install into the boat. After teardown, I discovered the 5.0 ran lean and "tuliped" an intake valve in the problem cylinder. The bottom end and heads are in good shape and the motor overall looks healthy. I estimate I can do a full rebuild for ~$500 (full gasket set, bearings, and intake valves) Before I tore down the motor, I talked to my machine shop about a 350 MPI build and they quoted me $3,330 for a fully remanufactured long block (gadgets, head work, and all new bearings/crank work). Additionally, I have an extra 350 MAG MPI wiring harness with semi-batched injection support and 2 knock sensors ready to install on the long block. I will also need to have my ECM555 remapped for the larger engine along with my Bravo 3 props re-pitched for ~1k. I plan on using the boat to cruise the CT River and Long Island Sound with approximately 6 people and occasional watersports. My question is: Is it worth the extra cost of ~$4,000 and the headache to upgrade to the 350MAG while I have the motor out?
 
Evan Mainetti said:
Hi all! I purchased a project Sundeck 240 with a low-compression 5.0 MPI motor over the summer but am now facing a difficult decision on which engine to install into the boat. After teardown, I discovered the 5.0 ran lean and "tuliped" an intake valve in the problem cylinder. The bottom end and heads are in good shape and the motor overall looks healthy. I estimate I can do a full rebuild for ~$500 (full gasket set, bearings, and intake valves) Before I tore down the motor, I talked to my machine shop about a 350 MPI build and they quoted me $3,330 for a fully remanufactured long block (gadgets, head work, and all new bearings/crank work). Additionally, I have an extra 350 MAG MPI wiring harness with semi-batched injection support and 2 knock sensors ready to install on the long block. I will also need to have my ECM555 remapped for the larger engine along with my Bravo 3 props re-pitched for ~1k. I plan on using the boat to cruise the CT River and Long Island Sound with approximately 6 people and occasional watersports. My question is: Is it worth the extra cost of ~$4,000 and the headache to upgrade to the 350MAG while I have the motor out?
Click to expand...
I had a 2005 240 SD with the 350 MAG. I wouldn't own that boat with a smaller motor.
 
I'd invest the $500 in the rebuild, sell the boat, then buy the one you want with the bigger motor.

If you figure it'll cost $4k to do the upgrade....you'll probably end up closer to $8k. It is a boat project, after all. :):)
 
Was this 5.0 a raw water Cooled salt water boat?

If so, don’t waste your money rebuilding 20 year old salt water heads. Buy new ones. Now re-budget your rebuild and see how how the two options compare (ie 5.0 vs 350 MAG)
 
Espos4 said:
Was this 5.0 a raw water Cooled salt water boat?

If so, don’t waste your money rebuilding 20 year old salt water heads. Buy new ones. Now re-budget your rebuild and see how how the two options compare (ie 5.0 vs 350 MAG)
Click to expand...
Yes, it is the base raw water-cooled motor, unfortunately. I am having my machine shop check out the heads and block , but the boat did a lot of sitting so the guides are not warn and the seats are in good shape with little carbon buildup.
 
Evan Mainetti said:
Yes, it is the base raw water-cooled motor, unfortunately. I am having my machine shop check out the heads and block , but the boat did a lot of sitting so the guides are not warn and the seats are in good shape with little carbon buildup.
Click to expand...
That’s not the reason. Salt water is corroding the cooling passages and they will eventually rot through.
 
Evan Mainetti said:
Hi all! I purchased a project Sundeck 240 with a low-compression 5.0 MPI motor over the summer but am now facing a difficult decision on which engine to install into the boat. After teardown, I discovered the 5.0 ran lean and "tuliped" an intake valve in the problem cylinder. The bottom end and heads are in good shape and the motor overall looks healthy. I estimate I can do a full rebuild for ~$500 (full gasket set, bearings, and intake valves) Before I tore down the motor, I talked to my machine shop about a 350 MPI build and they quoted me $3,330 for a fully remanufactured long block (gadgets, head work, and all new bearings/crank work). Additionally, I have an extra 350 MAG MPI wiring harness with semi-batched injection support and 2 knock sensors ready to install on the long block. I will also need to have my ECM555 remapped for the larger engine along with my Bravo 3 props re-pitched for ~1k. I plan on using the boat to cruise the CT River and Long Island Sound with approximately 6 people and occasional watersports. My question is: Is it worth the extra cost of ~$4,000 and the headache to upgrade to the 350MAG while I have the motor out?
Click to expand...
Did you find the root cause of this damage?
 
Seems like a 240 is a whole lot of boat for a 5.0. Would thing the 5.7 would be the minimum I would go and seriously consider bumping up to the 6.2.

The bigger the C.I. / torque the less the engine works hard to keep up on speed / load.
 
The 350 MAG is the perfect engine for that boat…. Don’t go smaller or bigger. I have had 4 of them over the years and always the 350 MAG…. You have one of the best boats Searay ever made it will hold its value
 
Bill Curtis said:
Seems like a 240 is a whole lot of boat for a 5.0. Would thing the 5.7 would be the minimum I would go and seriously consider bumping up to the 6.2.

The bigger the C.I. / torque the less the engine works hard to keep up
On speed / load.
Click to expand...

I had for +10 years a heavier 2006 240 sundancer with a 5.0mpi/b3 and regarding power the motor had always enough to to the job and have fun . Of course its not a racing boat , but thats also true for a 350mag mpi .

Since the 350 is not worlds apart from a 5.0mpi i personally would not the the pain and extra $$$ to reprop and remap the ecu . But of course everybody decides on own preferences. .
 
aerobat77 said:
I had for +10 years a heavier 2006 240 sundancer with a 5.0mpi/b3 and regarding power the motor had always enough to to the job and have fun . Of course its not a racing boat , but thats also true for a 350mag mpi .

Since the 350 is not worlds apart from a 5.0mpi i personally would not the the pain and extra $$$ to reprop and remap the ecu . But of course everybody decides on own preferences. .
Click to expand...
No problem. I get it.

But my comment was coming from the owner of a 22 foot Cuddy with a 454 Mag and B3. LOL. Consider the source.
 
The 240 is ruined with a 5.0. Such a great boat needs a real motor. This may be a blessing in disguise.
 
Espos4 said:
Here’s a 5.0 vs 350 MAG comparison.

Click to expand...

Thats about what my real life experience was on a 5.0mpi vs 350mag mpi . The 350 has a noticeable but not dramatic better hole shot . The top speed is only slightly better with the 350 and the overall fuel economy a bit better with the 5.0 .

If i would be seriously considering repowering with more whooomp i would go with something more noticeable like a 6.2 , 377 stroker etc .
 
Espos4 said:
That’s not the reason. Salt water is corroding the cooling passages and they will eventually rot through.
Click to expand...
Plus rebuilt heads are around $250 each so not worth paying a machinist to pressure test and do a valve job on 20 year old raw water cooled heads.
 
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