engine ???s for the pros

[shackdaddey]

i have a omc 305 v8 frozen up. i dont know if the block may be cracked but i was wondering if a standard 305 car block is the same .i know that the internals are different but what about the block.is it the same bell housing pattern?also i have a short block 350 mercruser could i just bolt all my heads and omc stuff on that will it be all right? i know my compression ratio will go up from the heads but there are tricks around that.i am a car mechanic but i dont know to much of the marine world thanks in advance

 

[KaGee]

Re: engine ???s for the pros

To answer your first question, the only difference in a 305 marine block and a 305 auto block is the cam and soft plugs. Just make sure you replace with one of the same vintage.<br /><br />Yes, a 350 will bolt up to the bellhousing, the question remains if the flywheel and coupler are the same as you have now. You might have to play around with that. You'll need the correct 350 heads. There is no difference between "auto" and "marine" in that area. A lot of the "auto" "tweaks" are counter productive to proper marine performance. <br /><br />However, it's your boat, do whatever ya like!

 

[Bondo]

Re: engine ???s for the pros

The Bare Blocks Are the Same,... Provided the Vintage is the Same........<br /><br />A 350 motor will work Just Fine,...... <br />But Not with 305 Heads,....Not only will the Comp. ratio be Too High,.....<br />The 305 heads Just Don't Flow well..... The motor will be a DOG....<br />

is it the same bell housing pattern?

A Chevy is a Chevy is a Chevy,.......They'll All Interchange...........From the 2.5l to the 7.4l.......<br />

i know that the internals are different but what about the block.

Not as Different as you Think.........<br /><br />Other than Brass Core Plugs,......... A SBC Truck engine is a Bolt in,+ Run..........<br />RV cams,+ Marine cams are Very Close to being the same.......

 

[shackdaddey]

Re: engine ???s for the pros

thank you for the info.i would be better of doing the 350 instead of the 305.a friend has a short block 350 car engine .060 over on the bore all i need to do is the cam swap right???

 

[Don S]

Re: engine ???s for the pros

I sure wouldn't recommend going to an engine .060 over. They just don't hold up that well in boats. Even the manufactures recommend not going over .030

 

[shackdaddey]

Re: engine ???s for the pros

.060 over is not that big 1.5mm overbore why do you say that besides what the factory says.its not that i dont believe you but i would like to know why.thanks

 

[shackdaddey]

Re: engine ???s for the pros

also one more ? you said the 305 heads do not flow well.i would assume thats with a 350 block but do they flow well on a 305 block.i want to do some performance work to the engine but people tell me throw out all i know about car engines cause it does not apply to the marine world.port and polish heads?? was told to polish bit not port due to the fact i will lose torque if i open them up? what do i believe and what do you guys recomend? the 305 is for a 25 ft bayliner but i also working on my 23ft scorpion and want to build a wicked 3590 for that. the bayliner im not sure if i want to do any perfrmance work to that it maybe a little underpowered. what do you say about the situation? thanks

 

[Don S]

Re: engine ???s for the pros

.060 over is not that big

It is "That Big" when boring a block on a marine engine.<br /><br />

why do you say that besides what the factory says

Experience....... I have seen a lot of .060 rebuilds sieze pistons.<br /><br />Cars aren't run at 4000+ Rpm's for hours on end at full load. Therefor the .060 overbore isn't that much of a problem.

 

[KaGee]

Re: engine ???s for the pros

I believe there is only about a 25-30 HP difference between the two, maybe a few more ponies if you go Vortec.<br /><br />Bondo was refferring to using 305 heads on a 350 block.<br /><br />If you want to know more what specifically to do to hop up your motor, try and find a copy of Dennis Moore's book on marine SBC's at the library.

 

[shackdaddey]

Re: engine ???s for the pros

thanks for the info i believe what you said. i want to get her done right the first time and am weighing out options thanks i will look for that book

 

[Always Broke]

Re: engine ???s for the pros

Don’t forget to take these things into account that I can think of off the top of my head. If your boat is raw water cooled the water circulating pump is different, it has a ceramic seal, and either a stainless or bronze impeller. A regular auto pump would rot in no time. The starter, alternator, distributor and any other electrical components are either sealed or vented to prevent sparks in your engine compartment, not a good thing. The plug wires usually have stainless contacts to prevent corrosion and keep a good connection. If it has a carburetor it may be designed to allow for being tilted and shook around and still be able to draw fuel and not spit it out the vent. The heads and cam are usually set up for low end power so unless you want to start messing with different props and screaming your motor to get your boat to run right stick to the right heads and cam for a longer motor life. Another way to think of having the right set up for a marine engine is taking your car and floor boarding the gas peddle for an hour or two, how long do you think it would last if it’s not set up to take that kind of punishment? If you go with the 350 get as many matching parts as you can off your 305 and save yourself a lot of future aggravation by setting it up the way it should be.

 

[rodbolt]

Re: engine ???s for the pros

not only does it have to be able to run at 4K for hours it alsohas to idle smoothly below 700 RPM for hours. if it cant idle below 700 you start eating shift clutches and couplers.<br /> and just like in the automotive world, speed costs money. how fast do ya wanna go ?