350 to 454 upgrade?

[Silly Seville]

After doing a search on this subject and reading about 20 mostly unrelated threads, my eyes are glazing over...but I will risk asking the question. Is a direct swap of a marine 350 to marine 454 an uneventful task, or must a number of items be replaced to make the exchange successful? My biggest concern is motor mounting points and exhaust risers lining up with existing points at Y pipe. I know the 454 is a big block (thus wider at heads) so I am imagining exhaust system will be an immediate issue. What about Alpha 1 ratios? Are there great enough differences in engine speeds to warrant changes in uppercase gearing? Thanks for your opinions/experiences/knowledge in advance!

Edit: After further reading, I am now aware that the gimbal housing may have to be changed as well? Any other major systems?

 

[greg82255]

Re: 350 to 454 upgrade?

You should really change out that alpha drive for a bravo setup. The massive amounts of torque a big block produces at lower RPMs will tear up the alpha drive. There are many threads that debate this topic hidden in the archives - I contemplated doing exactly what you are thinking and did some research a few months ago. The front motor mounts also may be different for a big block.

 

[Bondo]

Re: 350 to 454 upgrade?

After doing a search on this subject and reading about 20 mostly unrelated threads, my eyes are glazing over...but I will risk asking the question. Is a direct swap of a marine 350 to marine 454 an uneventful task, or must a number of items be replaced to make the exchange successful? My biggest concern is motor mounting points and exhaust risers lining up with existing points at Y pipe. I know the 454 is a big block (thus wider at heads) so I am imagining exhaust system will be an immediate issue. What about Alpha 1 ratios? Are there great enough differences in engine speeds to warrant changes in uppercase gearing? Thanks for your opinions/experiences/knowledge in advance!

Edit: After further reading, I am now aware that the gimbal housing may have to be changed as well? Any other major systems?

Ayuh,... Most of the bolt holes will line up Ok, but as Greg says, the Alpha drive, Don't like BBCs...
That's Why Merc invented the Bravo...

 

[HT32BSX115]

Re: 350 to 454 upgrade?

What about Alpha 1 ratios? Are there great enough differences in engine speeds to warrant changes in uppercase gearing? Thanks for your opinions/experiences/knowledge in advance!

Howdy,


Most of the 454/Alpha boats used a 1.36:1 ratio I think.... I know the 454 was available (new) in my 1987 211 Liberator but my brother chose to get it with a 460 OMC King Kobra!!(he wanted the extra HP!!! 340 vs 330!!!) I fixed it when I got it..(see my sig)


A LOT of boats in 1987 came with Alphas and 454's. In 1988 Mercruiser started offering the 454 with a Bravo I (for a reason....the biggest one was that MANY Alphas self destructed with a BBC in front of them!!))


So, you can do it.............But if it were me, I would do it with a Bravo.





Regards,


Rick

 

[TilliamWe]

Re: 350 to 454 upgrade?

Ayuh,... Most of the bolt holes will line up Ok, but as Greg says, the Alpha drive, Don't like BBCs...
That's Why Merc invented the Bravo...

Exactly right. Most measurement of a BBC aren't that much different than an SBC. My dad swapped a 502MPI in place of a 5.7LX and it was pretty straight forward.

And you "could" run an Alpha One Gen 2 behind a standard 454 and get away with it, if you aren't hammering the throttle all the time, or getting the hull out of the water on waves/wakes.
If you have a 1.47 gear ratio in an Alpha One Gen 2, you'd find a prop that would work. It might be a 25 pitch or a 26 pitch and little hard to come by, but they are out there.

 

[Silly Seville]

Re: 350 to 454 upgrade?

Ah, very good information...thank you all! And I'm glad to see the immediate consensus on the need for a B1 drive. I do remember last year looking at a prospective boat that had a factory 454/A1 combo and thought it strange that such a large motor would be mated to a light duty drive. Now I understand completely why that combo was dropped so quickly from the Mercruiser lineup. I was content with the potential of replacing the upper to attain the correct gearing, but am not interested in an entirely different (and more expensive) drive. I will stick with the 350/A1 combo I currently have. Thanks again for your thoughts!

 

[PBarrett]

Re: 350 to 454 upgrade?

I wouldn't say that you are stuck by any means. You could always put a 383 in your boat and get performance similar to the 454, but without the weight penalty. A properly built 383 Vortec will be at the the 300 HP limits of the Alpha drive, but if you you don't get carried away with your right hand your Alpha 1 will be just fine. The 383 will probably yield the best performance relative to cost. This is a pretty common upgrade, so there is lots of info out there on this board, plus others.

PB

 

[TilliamWe]

Re: 350 to 454 upgrade?

Good advice PB. Good last name too!

 

[Silly Seville]

Re: 350 to 454 upgrade?

You could always put a 383 in your boat and get performance similar to the 454

OK, I'm intrigued by this 383 idea...since the motor is just a stroked 350, does ANYTHING else need to be modified at great expense to make the swap? And, would a prop change mitigate the slightly different crank rpm's or even be necessary? Thanks again!

 

[RogersJetboat454]

Re: 350 to 454 upgrade?

OK, I'm intrigued by this 383 idea...since the motor is just a stroked 350, does ANYTHING else need to be modified at great expense to make the swap? And, would a prop change mitigate the slightly different crank rpm's or even be necessary? Thanks again!

Nothing drive wise should need modification. If you build a stroker all the mods are gunna take place w/ the block. I would recommend using an internally balanced stroker crank, with the same type of rear main seal style you are using (if you don't plan on stroking the original engine). That way there may be a chance you could use your original flywheel (if you use a diffrent block, you need to be sure the block is drilled for the right starter to use your old flywheel). May need to change props, best thing you can do is see what the original prop does with the new engine, and go from there.

 

[Silly Seville]

Re: 350 to 454 upgrade?

Thanks Roger! I was actually considering just buying a crate 383...I've seen a number of them for sale during a quick internet search in the 2k to 3k range. Should I buy a built short block and use my existing heads and cam, or get a long block and specify an RV cam be installed? (My block is unusable)

 

[PBarrett]

Re: 350 to 454 upgrade?

Nothing drive wise should need modification. If you build a stroker all the mods are gunna take place w/ the block. I would recommend using an internally balanced stroker crank, with the same type of rear main seal style you are using (if you don't plan on stroking the original engine). That way there may be a chance you could use your original flywheel (if you use a diffrent block, you need to be sure the block is drilled for the right starter to use your old flywheel). May need to change props, best thing you can do is see what the original prop does with the new engine, and go from there.

Very good advice.

There is nothing real difficult about building a 383, but you really need to do your homework if you plan to go this route. First and foremost you need to find a GOOD machine shop that has some experience in building a 383. Then you have to decide on the components that will go into the build, because they will determine the compression ratio, rod length, cam profile and balance of rotating assembly. A PROPERLY designed and built 383 will offer good mid-range torque (cruising speed) and good high end power (speed), while still being somewhat stingy on fuel.

If you look around you will see prices from $3700.00 for a long block to over $8000.00 for a complete engine. You don't have to spend that kind of money!! Depending upon how crazy you get with the internal parts, you can build a 383 for little more than a standard rebuild. Unless you plan to go racing, you don't need forged pistons, a four bolt main block, after market rods or any of the high performance parts. Just a nice Vortec head, roller cam 383 is all you need in front of your Alpha drive.

PB

 

[Silly Seville]

Re: 350 to 454 upgrade?

Thanks PB! I've been perusing the net until my eyes glaze over looking for info on this creature called 383 Stroker...and I'm loving what I've seen so far! I don't have a donor block available but I am aware that used 350's are everywhere for cheap, so my question to you is; should I have one built from scratch, or order a crate motor? This is going in a 27 ft. cabin cruiser, so neck-snapping holeshot, high speed pursuit and wave jumping are not in it's future. Ultimately, I would just like to have more horsepower on tap, without the weight penalty of a big block and having to upgrade the outdrive. Is a full roller motor really necessary, or can I exist peacefully with a flat tappet?

 

[Eric.G]

Re: 350 to 454 upgrade?

Google Merc Part # 807447A12.

325 HP from a Carb'ed Vortec 350 CI dressed motor for about 4k
Oilpan, Dist, Wiring, Eldbk RPM Alm Intake, Web Carb. Pre-fired from Mercruiser.
With the Bravo engine going in front of an Alpha drive, the only difference I've found is the wiring does not complete the circuit for the shifter cutout switch (although the correct wires are in the harness), so you'll need to run your own wire from the Grn/white of the cutout switch to the + side of the coil.
I've got about 10 hours on mine so far and its been great. Running a 24'' stainless prop in a 20.3' stingray.

Eric

 

[TilliamWe]

Re: 350 to 454 upgrade?

Seville, what year is your current 350? The only issue I forsee you having has sort of been mentioned. The 2 piece rear main seal that the 383 will have versus the possible 1 piece rear main seal your 350 may have.

 

[Silly Seville]

Re: 350 to 454 upgrade?

what year is your current 350?

That is a good question...boat is an 86, but engine may not be the original. What is the significance of the two different rear main seals? Starter to flywheel compatibility as Roger mentioned?

 

[FreeBeeTony]

Re: 350 to 454 upgrade?

How about starting with something like this?

http://cgi.ebay.com/ebaymotors/SBC-...r_Truck_Parts_Accessories&hash=item1c1e1f67bb

or better yet this..........

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=370450882648

 

[TilliamWe]

Re: 350 to 454 upgrade?

.. What is the significance of the two different rear main seals? Starter to flywheel compatibility as Roger mentioned?

Yes and the coupler required.

 

[Silly Seville]

Re: 350 to 454 upgrade?

Rats! I'm glad you mentioned that because I just discovered the difference in crankshaft bolt pattern sizes. Now I MUST get the numbers from my block to see if it is a 1 or 2 piece before I buy another motor. I ran the Mercruiser serial number and it confirms what "should" be in the boat except that there is a 4 barrel carb on it that was apparently supposed to be a 2 barrel? And if I understand the blogs and forums I've read thus far, the change occurred in 86 or 87...I'm stuck right between those years as the boat was made in summer of '86.

 

[RogersJetboat454]

Re: 350 to 454 upgrade?

Rats! I'm glad you mentioned that because I just discovered the difference in crankshaft bolt pattern sizes. Now I MUST get the numbers from my block to see if it is a 1 or 2 piece before I buy another motor. I ran the Mercruiser serial number and it confirms what "should" be in the boat except that there is a 4 barrel carb on it that was apparently supposed to be a 2 barrel? And if I understand the blogs and forums I've read thus far, the change occurred in 86 or 87...I'm stuck right between those years as the boat was made in summer of '86.

You can have an engine built, or build the original engine as a 383 stroker, regardless of the type of crank used. Back in the old days when people first started building 383's, they were using real 400 cranks which only came in 2 piece rear main seal (400's were produced from 1970-1980, so fell short of the switch over to 1 piece RMS in '86). That would limit the crank to only being used in a 2 piece rear main seal block. Now a days, most people are building 383's with aftermarket cranks. Aftermarket stroker cranks are available for both 2 and 1 piece rear main seal engines. There is also a company that offers a conversion so that you can use a 2 piece rear main seal crank in a 1 piece block (can't remember the name, but really shouldn't be necessary anyways). If you want to build this your self, there are allot of stroker kits that come with all the fixen's pre-balanced by the company. I would just be sure to get a kit with a marine friendly compression ratio. You will still need the machine shop to bore at least .030 over (for a true 383), and relieve the oil pan rail to clearance the rod bolts. You may also need to use a reduced base circle cam to clear the rods too (this depends size/shape of the rod's). The other benefit with going for the aftermarket crank is you can get a forged crank if you desire (cast ones should work fine as well), and you are not dealing with a crank that's at least 31 years old.