Swapping a 305 for a Jasper 383

[DaNinja]

My mechanic is trying to talk me out of it, but I think all bolt-ons should work fine. If I upgrade the intake and carb, that may add some work, but I think everything from the 305 should bolt up to a 383..

Am I missing something here?
I think I can stay within the capabilities of a fresh Alpha I with a mild 383.

 

[Captain Crispy]

Why is the mechanic trying to talk you out of it ?

 

[DaNinja]

Why is the mechanic trying to talk you out of it ?

He talked about the rigging and was concerned that I may over power an Alpha I.

 

[JUST PULLIN MY DINGHY]

As long as you get the same style block like vortec all parts are no different blocks are the same .If you use different style blocks like pre 85 vs vortec the intakes are at different angle because of the heads. A 383 is a 350 with a 400 crank lots more torque and hp its gonna want a little more fuel then a 305 so a bigger carb will probably be needed .As for the alpha1 as long as you dont do jack rabbit starts it should last ? good luck .:smt101

 

[Ididntdoit]

Mercruiser put alphas behind 454s and boat manufacturers put the combos in some petty heavy boats (I'm thinking 80s 260da?)- those were known to have some issues......I would think you would be fine with a light boat and the 383 which would still have significantly less torque than a big block

 

[DaNinja]

Most likely the gear ratio of your alpha drive will need to be changed. That would incurr extra costs, or you could sell your drive on ebay, and buy one on ebay that is the correct ratio. Without looking it up, I imagine the 383 would require a 1:47 to 1 ratio.

My manual says Merc used a 1.5:1 til the 260 5.7l.

I may want to rethink putting a 383 in front of the Alpha.
I can just imagine fixing her boat after I broke it, and then fragging the drive.

Good replies and advise.
I definitely have some question to ask my mechanic.

 

[Captain Crispy]

You have two issues then- can the alpha handle the additional torque of the 383, and can it handle the extra horsepower ?

The 383 makes a little more torque than the carbed 350, but not alot more. The more important issue will be RPM's. The extra horsepower of the 383 mostly comes from higher RPM's. Not sure that your existing Alpha can take the extra RPM's, but unless you are running it at full throttle alot it won't matter.

as someone else stated, you may need a new ratio, but you will be fine with the 383. You could just sell the one you have, and get a new drive with a three year warranty from SEI at a new ratio.