Cost / difficulty of swapping a 5.0 MPI for an 8.1 MPI?

[KD4UPL]

I've been looking at boats in the 24' range. I tend to go out with 10 or more people so I'd really like to have a big block. Many of the boats available have the little 5.0 MPI engine which is of course less expensive and they are much more plentiful. I got to wondering what would be involved with swapping the engine. I want a Bravo 3 drive anyway which many of the 5.0 boats have.
So, assuming a B3 already, is it that big a deal to swap in a big block? What would a used 8.1 sell for? What could I expect to get for the removed 5.0 to help defray the costs? Would the gear ratio in the drive or the props need to be changed?
I'm sure it's probably less expensive to just buy a boat with a big block to begin with but maybe I'm wrong. I'd like to have an idea of the cost of the swap for comparison. I think I could probably pull the old engine myself but I'd need to pay someone to install the new one to get it properly aligned.

 

[Scott Danforth]

Used 8.1's are about $7k without drives. You could build a 454 with a stroker kit to get you 8.1 liters with well over 500hp for $4k, then add exhaust

 

[alldodge]

I recommend staying away from 8.1, go with the 7.4 and at the most 8.2. All should bolt up, but a 7.4 would take you to 55 to 60 and a 8.2 would take you in the range to 70 mph. That said, check the boat and make sure it is allowed to have that much HP.

As for the buy one sell another, if you have time you can get a deal, if not it will cost more. If money is of little issue, no problem. My time frame for the great deal is one to two years, if could take a week, but could also take much longer.

 

[KD4UPL]

Okay, what's wrong with the 8.1? Why do you recommend against them. Is that in general or just in reference to a swap?

 

[tpenfield]

Perhaps look for a 26' boat that has a big block engine instead of a 24' boat that needs a swap.

 

[alldodge]

Okay, what's wrong with the 8.1? Why do you recommend against them. Is that in general or just in reference to a swap?

The 8.1 will cost more then the other BB's because there is not that many of them. There has also been some growing pains with them but are a good motor.

 

[burtonrider11]

I have to agree with Ted above. I think if you are normally going to be bringing 10+ people out, a 26 would make more sense as it will probably be easier to find with a BB from the factory. I can't see a scenario were it would be cheaper to make the swap than to just go a bit bigger and get the boat rigged the way you want, from the factory.

Someone will know better than I, however I don't believe the engine mounts to be the same for the SBC's vs BB's. It's worth looking at what a turn key 8.1 goes for from a reputable dealer:

http://www.michiganmotorz.com/complete-turnkey-engines-turnkey-engines-c-31_49_79.html

They also have re-man'd blocks, but you'd need intake, exhaust and EFI:

http://www.michiganmotorz.com/marine-engines-remanufactured-marine-engines-c-31_51.html

I am sure there are a few manufacturers that have a 24' boat with BB's, you'll just have to find them! Good luck in your search!

 

[HT32BSX115]

I've been looking at boats in the 24' range. I tend to go out with 10 or more people so I'd really like to have a big block. Many of the boats available have the little 5.0 MPI engine which is of course less expensive and they are much more plentiful. I got to wondering what would be involved with swapping the engine. I want a Bravo 3 drive anyway which many of the 5.0 boats have.
So, assuming a B3 already, is it that big a deal to swap in a big block?

It's probably not all that hard to do the swap but if you do, you might have to re-do the front engine mounts and obtain all the accessories. (to include manifolds, risers and plumbing parts) (I think the Y-pipe might be usable though)

Also, a Bravo III behind a 5.0L engine in a 24ft boat will likely be 2.20:1 ratio and it might be a 1.81:1 behind a 454/496 engine.
(my 1997 454/Bravo III came out of a 24ft Bayliner. It's a 1.81:1 drive and I use 26p props in my 21ft FourWinns)

So starting with a 5.0L V-8 + 2.20:1 drive....... the drive ratio may be all wrong for a BB forcing you to run 28p or 30p props (possibly too high for a big bowrider)


73/Rick

 

[Scott Danforth]

FWIW, my buddies Searay 240 deck boat has a 6.2/bravo and will hit 55mph and has no problem with 10people on board (although it is crowded). his next boat will be a cruiser with twins for overnighting

 

[HT32BSX115]

FWIW, my buddies Searay 240 deck boat has a 6.2/bravo and will hit 55mph and has no problem with 10people on board (although it is crowded). his next boat will be a cruiser with twins for overnighting

I had 10 people in my FourWinns (counting the 3 BIG dogs!) and it was WAY crowded! (It was on Lake Tahoe and it would do about 40mph too! If I hadn't had the Bravo III, it probably wouldn't have even made it up to a plane.....)

 

[Scott Danforth]

I agree, for 10 people 26' or larger is recommended. even though the cap plate on a 240 deck is 13 people, anything more than 7 and it gets crowded quickly. My cuddy is rated for 12, however, 6 is max comfortably (where your not sitting on someones lap), 4 with the dogs.

 

[thumpar]

Why not just buy a boat with the engine you want? I can understand if you wanted to upgrade something you already own and like. Just keep looking until you find one with the engine setup you want. It will be cheaper in the long run.

 

[KD4UPL]

Thanks for all the help guys. One of my favorite (and closest lakes) has a length limit of 25'; that's one reason I'm not looking too hard at 26' boats. My 20.5' Larson was rated for 11 people and we often had 10 or 11 on it so even a 24' will feel like we've got a lot more space. I am going to continue looking for one with a BB, I'm in no hurry. I hadn't thought much about the 6.2L, those really are rare. I thin I've only ever seen 1 boat list that engine.

 

[bruceb58]

My 24' has a 454 but not fuel injected. With the 8.1 you have to have closed cooling which you don't have to have with a 454 although if I put in a new engine, I would definitely put in.

 

[Mischief Managed]

My advice would be to wait for a boat with the engine you prefer and expand your search to areas far away from you. It took me a year to find my 7.4 MPI-equipped 25 footer (most came with 5.0s), and I had to drive 2000 miles round-trip to get it, but 11 years later, I still love the boat and I'm still really glad I was patient and willing to travel.

 

[harleyman1975]

I'm guessing a 6.2 is a stroker....just right from merc. it must be a 383 or 377...correct? any way a stroker would be a viable swap as it is a small block with big block torque.

 

[thumpar]

The 6.2 is a 377. Basically a 400 crank in a 350 block. The 383 is the same thing just bored out. One of my customers has twin 6.2l bravo 1 setups on his Formula 32'. He loves them.