building a 350 4bbl engine

[lime4x4]

My current boat 268 searay weekender needs more power.When fully loaded up with gear,people and fuel she probably weighs close to 7500 to 8000lbs. Needless to say with a single stock 260 hp engine it's under powered.So my choices are either build up a 350 or install a big block. Would rather just build up a 350.What type of cam and pistons should i use? The boat is a 1986 350 4bbl carb.Already got the stuff to convert over to vortec heads. I have a newer style block that can use either a reg or roller camshaft.

 

[Mkos1980]

Re: building a 350 4bbl engine

Keep the stock shortblock the way it is and add the vortecs. If you want to cam the motor, I would look into the Crane compucam (powermax) 2032 214/220 450/465 112LSA . The stock vortec springs will take the lift, but thats about it. If you upgrade the vortec springs to a Comp 981 or beehive setup then you will be able to run one of Comps Extreme Marine cams along with screw in studs or just pinning them.

Seeing that your not a go fast boat, I personally would stick with the shortblock you have, throw the vortecs on and add the GM Ramjet Roller camshaft (Its accually the stock MerCruiser roller one too) and an edelbrock performer rpm intake. The RPM intake is accually a highrise intake which is stock on the 350 Magnum motors.

 

[lime4x4]

Re: building a 350 4bbl engine

i know it's not a speed demon that's for sure. just don't like running it in the hi 3000 rpms to keep her moving

 

[marine4003]

Re: building a 350 4bbl engine

Lime..Is she freshwater cooled,or raw water,when i beefed up my motors (850hp each) i found the raw water wasn't enough to keep them cool,switched to closed system,adding HP is great, but what your after is torque, consult a good marine mechanic before you drop a dime,might want to repower with a 454.

 

[Malibud]

Re: building a 350 4bbl engine

there's no replacement for displacement

 

[lime4x4]

Re: building a 350 4bbl engine

raw water cooled. Yeah i'm leaning towards the big block idea just more of an expense

 

[FreeBeeTony]

Re: building a 350 4bbl engine

Is it an inboard or an I/O?

How about a stroker?

 

[TilliamWe]

Re: building a 350 4bbl engine

Lime, have you considered the Mercruiser 383MAG MPI? It won't be as torquey as a 7.4, but it would be an improvement over most any 5.7 you could build. Plus it would be a little easier on your Alpha drive. They aren't cheap, but they are a complete engine package. Drop it in, attach starter wires, the fuel line, and plug it in, and you are ready to go.

 

[TilliamWe]

Re: building a 350 4bbl engine

My current boat 268 searay weekender needs more power.When fully loaded up with gear,people and fuel she probably weighs close to 7500 to 8000lbs.

If it's actually the Sundancer with an aft cabin, then 8000 is the least it weighs! My dad's 89 weighed almost 11,000lbs on it's tandem axle steel trailer!

 

[fishmen111]

Re: building a 350 4bbl engine

Best of both worlds...put a SBC 400ci in there.

 

[mudweiser]

Re: building a 350 4bbl engine

there's no replacement for displacement

Here's how i see it: "There's no replacement for displacement, but nitrous can get you close".

Not to hijack your post, but in a similar situation myself. My boat is about 1/2 the weight of yours but still a 305 cid just don't do it. I have a 96 Vortec 350 sitting here and a 69 350 that i was going to build for my boat. Looked into making either into 383 stroker. Once your all done preping the block and building the heads plus buying the rebuild kit, you can get a crate engine or a fresh rebuild from a reputable builder for about the same money. I'm sticking with the 305 until this winter. However in the end, i think you'd have a high strung engine where a calm BB can do just as good. One thing i found, is will the outdrive take it?

 

[mtnrat]

Re: building a 350 4bbl engine

I just built a 383 for my boat. 375 hp and pretty flat 400lbs torque curve.
I researched for a long time for the combination and had Chris Straub from Straub technologies design and have the cam ground specifically for my combination and application. Had likely the best engine balancer in western Canada balance it. Just fired it up this weekend. Super smooth idle. No sea trials yet.
BTW it did cost me a lot and I have not added up the bills yet.
Some of the parts.
Enginequest Heads 200cc and 72cc combustion chamber.
SB Chevy 383 Mahle Forged Quench Dish Top Pistons
Scat 383 4340 Standard Weight Crank - 3.750" Stroke
Scat 4340 Forged Pro Stock SBC 6.000" I-Beam Rods - 7/16" Cap Screw.
Lunatti Roller retrofit lifters.
Clevite 77 bearings
RPM air gap intake
Q-jet jetted for 383
etc etc.
Static compression of 9.1:1

Having described all that I think you might be happier with a big block for your boat.