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Changing a 454 to a 350 ?

R

Richie-Cookie Green

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Have a 96 Proline 251 WA with a Mercruiser 454 w/Bravo 3 Outdrive and want to change it to a 350. Has anyone done this and are there any problems I should be aware of? Thx.
 
Ayuh,... Other than you'll need a Complete bobtail motor, 'n it'll be Way down on power,...

Go for it...
 
To the original poster, this very subject has been discussed many times and in many forums.

Yes if you wish to go to a 350 there is no major impediment, mechanical wise.

Most or everything from the flywheel back would not have to be changed.

However the is no substitution for torque, you may get close to the hp of a 454 with a 350, but not the torque unless you invest big money.

My question is why do you wish to change out to the 350 ? The 454 went? It blow up ?

What, just asking and if you reply we all of us here can explore your reasons and discuss it.
 
Yes, it would be interesting to learn why you are considering this.
If hell bent on going to the SB from the BB, have you considered the 377 or 383?
This can shave approximately 280lb from the stern, and if custom building a 377/383, it can be done using an array of pistons, none of which would be the fully dished piston.
If so, you can gain some fairly good torque numbers, and achieve a good hp number.
Even if you were to custom build a 5.7L, get as far from the fully dished piston as you can! C/R can be near the same with the use of a correct profile D-dish, L/C Quench style, and/or Rev Dome........ anything but the f/d piston!
IMO, the 377/383 would make for a better BB replacement.
.
 
Well lets look at the HP rating for a 454 vs a 350

A 454 non HO is what......~ 300 hp - 330 hp. torque is close behind. ( I dont have the specs in front of me right now so I am guessing a bit)

A well biult 350, 383 (377 ?????? why??) even a 400 and a 427 or 454 small block, all can achive the same results as a standard 454 merc motor.

What about a LS motor?? the 6.2 litre....

It would be all about the parts combo's used.

Now I do not read he has this in mind but I am just sayin............it can be done.


Now If it were me I would be going in the other direction and making the 454 into a 500 ++ hp fire breathing dragon..............
 
Don't know much about it but, I froze and busted my 454 that is in the 96 Proline 251 WA and a friend suggested I make that switch to 350. He said it would lighten the boat and be better on economy but I am concerned about the torque not the HP. Haven't pulled the old motor yet just trying to find out my options. One of the main reasons I would entertain this is for space. With the 454 I cannot get to anything to work on it. Thanks!
 
Personally, the small block 383 is an amazing engine when it comes to HP / TQ. The HP/TQ numbers can easily match the 454, but will be achieved at a slightly higher RPM, which MAY need a new prop profile. But generally, the trade offs are a wash, PLUS smaller foot print and lighter weight of engine makes maintenance alot easier and in general, small block vs: big block parts are cheaper and easier to come by. Heck, you can go to Jegs and get a ready to run crate "Blueprint Engines SB-Chevy 383ci/ 405HP/ 440TQ", change a few things for a marine application, turn the key and away you go........ And that's a flat tappet motor. Add roller rockers, roller tappets and different cam profile and get even more out of it........ Just stay away from the 400 CI small block. The cylinders are siamesed (touching each other) in the water jacket and creates hot spots in the bores where they touch, causing havoc with the rings and pistons when run at higher loads for any sustained period, like every boat does. Not one of Chevy's brighter moments in engineering.

I have a 454 in my 2550 SX Chaparral and probably would not hesitate going to a 383 if and when the monster punches out. BUT Big Block certainly has that "whoh" appeal to it and has a sound to it few small blocks match. Like the old saying goes, "nothing like cubic inches" for torque and sound. The thought of a built 502 or 572 BBC (also available at Jegs) is certainly awe inspiring, but...............................
 
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Unless you have a very large wallet it is best to stay with what you have.

Going from a big block to a small block is more involved than just changing engine blocks. The exhaust manifolds are different, so new ones need to be purchased.
The accesories that are bolted to the big block may not fit in the same locations so a new belt(s) would need to be purchased. A marine engine block water pump,

You can use the ignition as the BB and SB are the same, the Ignition module is different but can be used. If you choose a SB with similar power than your carb can be reused but a new intake manifold will need to be purchased. There may be more..........$$$$$$$$$


Bottom line is if you can afford it and do most of the work yourself? Go for it!! If not a replacement 454 short block and just swapp all the parts is a lot cheaper and easier.


Just some food for thought.
 
Junk yards are choke full of supposed to be destroyed bbc. Good one 500 bucks maybe under a grand for sure.

Then just switch over the marine externals from the old motor.

Marine gaskets.
 
My guess is you are short of cash go for it then change to a more appropriate prop later
Richie-Cookie Green said:
Don't know much about it but, I froze and busted my 454 that is in the 96 Proline 251 WA and a friend suggested I make that switch to 350. He said it would lighten the boat and be better on economy but I am concerned about the torque not the HP. Haven't pulled the old motor yet just trying to find out my options. One of the main reasons I would entertain this is for space. With the 454 I cannot get to anything to work on it. Thanks!
Click to expand...
 
If you do a engine replacement then in order to avoid maintanence items you should ....

1. use a platium spark plug equal to the standard reccomended spark plug (heat range). You will get many many years of use!!
2. Go with a high end spark plug wire, A good set should also last years...
3. If you need access to the drain plugs make some fittings with hoses and easily removed plugs so they are running to a accessable area.
4. if it was not allready, have the oil filter within easy reach!!

Not much else I can think of that would be of concern.
 
Reducing power may not give the intended outcome (better economy). I repowered from a 235hp to a 300hp and economy improved to 3.4mpg from 2.25mpg.
 
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