BajaRunner

ok my dad has an older 20' boat that has a 198hp 350. he wants to juice it up a little. But he has a 454 engine out of an old truck.

besides new exhaust, what all would it take to do the swap. i think the flywheel is different, but everything else should swop out right?

Iggy

I would think a lot more has to be changed than the just the flywheel.
The engine bell housing is larger on the BBC, starter is different, engine mount location is different, cam change, exhaust manifolds, and probably many more things I didn't think of.
I'm guessing the boat has an Alpha or "R" drive which won't take the torque of a BBC.
He'd be better off warming up the 350.

Budman

It will probably be more trouble than it is worth. Aside from the drive probably not being up to the extra power, you will need to get the correct pulleys and brackets for the engine accessories, and you may have to change the motor mounts (although the motor mount location relative to the bell housing flange is the same between big block and small block). I did the same swap on my '88 Baja - but I also upgraded the drive to a Bravo. Oh, and if you have transom exhaust, you will find that the big block has wider spacing for the exhaust tubes. And yes, you will need the harmonic balancer and flywheel for a 454, since they are externally balanced.

Have you considered that the extra weight of the big block will probably throw off your center of gravity on such a small boat?

HyperBaja

If you do decide to swap it out, I am looking for a 350.

justinVIP

What 350 are you looking for? MPI or 260 HP?

BajaRunner

unless the "marine" version is different, a bell housing that fits a sbc and a bbc are the same.

engine mounts are the exact same.

cam is already in the engine.

starter is the same.

i would need new exhaust, and it has under water now, so i was going to convert it anyway.

the 454 is complete. other than changing pulleys to make the other stuff fit and the weight, i dont think it would be that hard.

i am worried about the drive. they did couple 454's to alphas but definately not optimal.

jafo

Yeah, they did, but almost always with the 1.32:1 gear ratio, and you could still gut the insides on that Alpha with a simple aggressive push of the throttle or one trip airborne.
BOOM- just a matter of when..........

Budman

Not trying to rain on your parade or anything, but the CG issue would concern me more than the drive. The drive can be swapped out easy enough while you have the motor out, but the extra 250 or so lbs of weight right at the stern may make the boat into an ill-handling, porpoising nightmare. I guess trim tabs could alleviate that to some extent, but then you are throwing more money at it.

Are you planning to use the carb that is on the 454 now? Keep in mind that you should be running a marine carburetor, and I doubt if a truck carb would qualify. If you are going to run the carb off the 350, you will probably need to rejet it. A truck cam should be pretty mild, so I would think that reversion would not be an issue. However, it probably has the small peanut port heads on it, so performance will be less. It might be more cost-effective to sell the 454, and use the proceeds from that for building up your existing small block. That way everything will bolt back in with a minimum of fuss. There are a lot of guys on this board who are getting some impressive numbers from their small blocks. Three hundred or so HP without the weight penalty of the big block might really wake up a 20-foot boat.

MKast

Pulled the cracked 260hp 350 out. Had 330hp MIE on the engine stand with fresh overhaul, Crane Blueprint cam(Mercruiser specs). Used stock 350 engine mounts on 454. You will need flywheel, from GM, drive coupling was modified to work on 454 flywheel. Starter must match flywheel, (EBay). Bell housing is the same. Exhaust manifolds from EBay, used original risers, spacing at Y pipe is the same. Had to slightly modify the cooling hoses, stock one inch hose from NAPA, $10 copper union from hardware store. Water pump (marine, EBay). Pulleys from 350 fit. Had to buy the power steering pump bracket from Mercruiser $100.
Dist. TB IV (EBay), get the right advance module it's different than the 350.
Sent drive for overhaul and gear change 1.5 to 1 Changed to 1.32 to 1, ($1000). The weight of the boat is the determining factor as far as the drive holding up to the bigger horsepower. The boat I put it in weighs 2650 empty. Alot of the 1988 454 Mag Alpha's you hear breaking were in big time heavy boats, some liked to run WOT across the pond. Lake Michigan. Mercruiser offered 454's with Alpha's for two years. Don't forget the drive shower. Handling has not been a problem, low speed or WOT.

Whiteknuckle

I think you should also consider that the starter, alternator, fuel pump, carb and maybe distributor should be of marine grade. Sparks in the engine compartment are dangerous. If you had a fire, the best you could hope for is no one gets hurt because your insurance sure won't cover a boat with non-marine accessories.