305 vs 350

[Chris]

I have a 2007 Sea Ray Sport 205. I have to replace the motor because failed to winterize boat. The one knock I have on the boat was the hole shot. Need more power to get bigger skiers up and going quicker. Considering upgrading from 5.0 to 5.7 carbureted engine but wanted to make sure that I wouldn't be causing another problem with drive etc. Looking for recommendation on what to do.

[wattaway2]

As a old drag racer -- ain't no replacement for displacement!

[flyingfrizzle]

Originally Posted by wattaway2

As a old drag racer -- ain't no replacement for displacement!

This is true, that's why I went from a 350 to a 400 but added a stroker crank and bored the block to 4.155 which gave me 434ci. The difference was enormous even with same heads and intake, but did add a larger carb.

For you a 350 or a 383 would be the ticket. Go efi if you want to save on fuel tho

[wattaway2]

Just a lil add on to my comment on the displacement issue -most small block chevy motors use the same bell housing pattern as well as the engine block mounts it's one of the things that makes them so popular I would check into just how much horse power the outdrive you are using will handle. I would think you would be fine but it's something to look at first I've seen a lot of the 383 sm block chevy advertised and can tell you from drag racing they are a great combination with great torque and hp that didn't seam to hurt itself with terrible crank shaft rod angles and such the 350 was also a great size

[flyingfrizzle]

I agree with that also, most stuff on small block chevys will interchange. Most of the mercursers and Volvos are chevy type blocks as well. 265-400 sbc are interchangeable long as they are the older gen type. Some of the newer style block will work as well but not all of them. Most of the big blocks have the same bell housing as well but everything else is different. Your 305 has a 3.736 bore and a 3.480 stroke, where an 350 has a 4.000 bore and a 3.480 stroke (Bigger pistons). Also a 383 is just a 350 (3.480) with a 400 crank shaft (3.875) in it, same blocks. Everything else is basically the same. You are mainly limited by how much power you drive can handle. There are many crank rod piston rebuild kits out there available to stroke the 350s to get the extra inches. The 434 sbc I have is a aftermarket block that is a basicly a 350. It has 350 main bearings but it has thick piston sleeves that are boreable to 4.250 which with a 4.00 stroke crank will make a 454 small block! I had mine bored to 4.155 so I had more left if I ever needed to rebore it. The 4.00 stroke crank in a 400 block will give you 426 ci but it will need modifying to make it rotate. The rod bolts will hit the rails the oil pan bolts too. They make special pans to clear the rods but you would have to cut grooves in the block to clear the rotation of the rods. The 383 kits are a bolt in type, not much modifications needed and like said it dose not cause bad angles on the piston / rods. Most kits are sold with 6.0 rods which helps the angle instead of 5.7 in rods. You do have to have the right pistons to match for the longer rods. The pin in the piston is higher up to make it work out right. This helps get rid of bad geometry and binds the pistons less. Mercusier makes a nice stroker 383 motor that would be a good bolt in replacement. Islandtrader put one in his 21 moesly hull. Those are great for extra power and are still extremely reliable.

434 sbc I built:

[BigLew]

First question. Is your outdrive mated up to the 350 CI block in other models of the manufactures line of engines. If yes, you should not have a problem.

If not, and this might be a less expensive direction, is looking at the drive ratio of the drive and changing that and/or prop changes as well.

Maybe Fr. Frank will chime in. He really seems to know this stuff. Send him a PM with ALL the information. Gross weight, HP, max RPM, current cruise and hole shot numbers, drive ratios, prop size and prop manufacturer info. He'll ask you for what else he might need. He likes feeling he is needed and he is!

[FishStretcher]

305 or 350, you probably want a better prop to solve your holeshot. And maybe a planing fin.

The difference in prop efficiency from an optimal to average prop can overshadow the difference between a 350 and a 305.

That said, if I had to repower, I would go with a 350 if the price were the same.