going from small block to big block

[scr350]

i'm wanting to change my vortec 350 to a 454 vortec. the boat is a maxum scr2300. i need more torque out of the hole. i have a 330 horse 350 in it now. my question is. can i keep my flywheel and bellhousing and coupler if i get the flywheel balanced with my new engine build up? thanks

 

[Gary H NC]

Re: going from small block to big block

What make and model engine and drive? Need way more info...

Sounds like a complete repower is what you are needing...If its an Alpha drive it will never survive a BB mated to it.

 

[zbnutcase]

Re: going from small block to big block

I agree, unless its a Bravo dont even think about a big-block swap. If I remember right Merc made a 454 Alpha package for like 1 year...and most came back as shrapnel. 'nutcase

 

[scr350]

Re: going from small block to big block

yes it is an alpha gen 2 the boat is a 1992 maxum2300....

 

[mkast]

Re: going from small block to big block

If its an Alpha drive it will never survive a BB mated to it.

Don't believe everything you read, my MIE 454 Alpha 1 is doing just fine.

 

[munsonbw]

Re: going from small block to big block

i'm wanting to change my vortec 350 to a 454 vortec. the boat is a maxum scr2300. i need more torque out of the hole. i have a 330 horse 350 in it now.

Perhaps the issue is that the current power plant is built for HP, not torque. 330hp out of a 350 is a pretty respectable number, but I would bet that your torque suffers as a result. Maybe do some digging and see what the torque curve looks like for other 350 mercs. A cam and intake change would move the power down lower? Also, changing your outdrive ratio and prop will help. You loose top end but will gain the lower power.

 

[boat1010]

Re: going from small block to big block

I am not sure what you are doing is what you want. My 7.4 is 330hp. but if you are just looking for more hole shot then I would look at some gears and prop first. Just my two cents.

 

[jaxnjil]

Re: going from small block to big block

Don't believe everything you read, my MIE 454 Alpha 1 is doing just fine.

if it came that way and hasn't been messed with it most likely will as was probably the rare heavy duty geared version.

standard duty alphas have very little chance of standing up behind the BB

 

[robjen1019]

Re: going from small block to big block

Its just me, but wouldn't going to a 383 be a much easier process. Plus, you won't add any extra weight, direct replacement, and you will gain the torque you are looking for.

 

[Gary H NC]

Re: going from small block to big block

Its just me, but wouldn't going to a 383 be a much easier process. Plus, you won't add any extra weight, direct replacement, and you will gain the torque you are looking for.

I was thinking that same thing..but if he is getting 330HP out of a 350 now would it be worth it?
That 330 HP sounds pretty high unless its already a built up 350..

 

[QC]

Re: going from small block to big block

I was thinking that same thing..but if he is getting 330HP out of a 350 now would it be worth it?
That 330 HP sounds pretty high unless its already a built up 350..

My guess is that it is less than 300 . . . Can defintiely be done and probably with more RPM which will cause poor hole shot unless geared down (higher numeric).

Maybe we should ask the Million Dollar Question . . . What's your WOT RPM? A stock, carbed 250 Merc will plane that boat fine. Even with a heavy load it will break 40 MPH. This is actual experience with that exact boat. Probably a 2000 year model.

 

[Bondo]

Re: going from small block to big block

can i keep my flywheel and bellhousing and coupler if i get the flywheel balanced with my new engine build up?

Ayuh,... Sure, but it'd be easier,+ probably Cheaper to use a 454 Flywheel...
The flywheel cover,+ coupler don't care...

as noted above,... What you want to do is Doable, but not the right direction to go...
If you're building this for Runnin',+ Gunnin',...
You'll have to consider the replacement price of the Alpha drive as an annual maintance expence...

 

[scr350]

Re: going from small block to big block

well what i'm looking for is more torque, i have a repower engine in the boat now from marine power but it has no torque. runs fine on the top end. when i load it up for a weekend on the lake with two kids all the food plus 2 adults it takes a while to plane out. i have trim tabs and a 16 inch 15pitch prop on it now. rpms top out at 4800. i usually cruise about 3800. i feel i can build this 454 to the 435 horse with no problems of reliability. plus after 8 seasons the 350 will need work pretty soon as it uses about a quart of oil every 32 hours !

 

[jaxnjil]

Re: going from small block to big block

you make the call. the couplers are interchangeable. the left is a bravo the right is the alpha.
you can bulid the 350 up to but you still havent said how your going to get the extra power to the water with your alpha drive.
you now say your 350 is tired. at least that what i read

plus after 8 seasons the 350 will need work pretty soon as it uses about a quart of oil every 32 hours !

any way no to the bell housing if you use the heavy duty coupler. they use different B H. if going heavy to lite then i think it would work but hole in lite duty is to small for the hd coupler. as far as fly wheel, not sure

 

[Bondo]

Re: going from small block to big block

i feel i can build this 454 to the 435 horse with no problems of reliability.

Ayuh,... That's all fine,+ dandy...
But,...
As noted above,... Your Alpha drive will Not take it...

 

[mkast]

Re: going from small block to big block

Time to sell the boat.

 

[scr350]

Re: going from small block to big block

well i cant sell the boat. i just finished setting it up the way i like it. a fishing machine with my boys. and a overnighter with the family. i guess i will have to do a complete repower. will the bravo 1 work or would the more desirable bravo3 be better. will the transom assembly for a bravo work on both types?
thanks for all the answers, i seen on my transom that the alpha 1 gen 2 should only be used up to 260hp. so either way that needs to be changed out!

 

[SuperNova]

Re: going from small block to big block

plus after 8 seasons the 350 will need work pretty soon as it uses about a quart of oil every 32 hours !

One,

Its just me, but wouldn't going to a 383 be a much easier process. Plus, you won't add any extra weight, direct replacement, and you will gain the torque you are looking for.

Plus one,
Equals 383.


Even if your old engine produced 330hp when it was new, I would think it would have ocurred fairly high in the rpm band and that alone would be enough to kill bottom end power.
Back to a basic lesson; engines don't produce "horsepower", they produce torque (they twist). Horsepower is a mathematically derived number.
hp=(torquexrpm)/5252
So let's try an experiment here; 400ft/lbs is a pretty strong 350, so let's plug that number into our equation and play a little.
An engine that produces 400 ft/lbs peak at 2000 rpm is only gonna show as 154 hp at 2000 rpm and 214 hp at 4500 rpm assuming it drops to 250 ft/lbs by 4500 rpm. Another engine that produces the same 400 ft/lbs, but peaks at 4500 rpm is 343 hp. So you have to ask yourself; Which engine "sounds" like a better engine? Which engine will actually work best in my boat?

 

[SuperNova]

Re: going from small block to big block

well i cant sell the boat. i just finished setting it up the way i like it. a fishing machine with my boys. and a overnighter with the family. i guess i will have to do a complete repower. will the bravo 1 work or would the more desirable bravo3 be better. will the transom assembly for a bravo work on both types?
thanks for all the answers, i seen on my transom that the alpha 1 gen 2 should only be used up to 260hp. so either way that needs to be changed out!

I personally wouldn't go through all that expense. A very solid 383 can be had a lot cheaper and will do what you need without all the headache. Unless, of course, you got the bucks to just tow it to the local boatyard and tell them to just go ahead and repower it with new engine and outdrive.

Hard to argue with new injected big-block with a Bravo 3 behind it.

 

[QC]

Re: going from small block to big block

Has she always performed the same? Top speed? Any more info on the engine you have in there? Why do you think it's 330 horsepower? Flywheel? Propshaft? I am guessing that a small block that was right would do an amazing job. I do not believe any rebuilders claims of small block marine power above 300 horse and even then I am guessing at the flywheel which is only 270 - 280 at the prop. No way you need 435 for this setup if your biggest concern is planing time. Why does planing time matter if she does in fact plane and she is fast enough at cruise?

Hey, I'd like to cruise at 60, so this is not about "you don't need to go that fast". I just want to understand your goals and/or complaint better.