Boat help

I'm looking for a lot of help. My father inlaw has a 26ft. cruise boat with a 305 chevy engine in it from what I'm told. It was made in 1982 its been sitting for over 13 years. We've been talking about getting it running but he's reluctant cause of the price of gas. I'm looking for information on swapping it over to a 6 or a 4 cylinder that would have enuff power to move the boat the same or better than the v8. I'm a good mechanic give me a hotrod or a fast bike and I don't need any help. I know very little about boats and don't know anyone who does. If someone could point me in the right direction that would be great.

 

There is plenty of information about that subject here. Look under marinizing, inboards, propulsion, diesel etc.

 

Unless it is mechanically hopeless, put your effort into the existing 305. Without switching to diesel you won't get a magical fuel effiency change between a v8, a 6 or a 4. The weight difference between the different motors will make a slight difference but on a 26 foot boat probably not a big deal. It takes the same amount of horsepower to move the boat and the horses come from the fuel burned. Each motor will have to consume roughly the same amount of fuel to provide sufficient horsepower for similar speeds. Boat motors are more like running a generator than running a car. Most of your time will be spent in steady state operation instead of constantly accelerating and deaccelerating. Once you've reached operating speed differences in carb engineering will start to flatten out.

Get that old motor running and enjoy the summer!

 

A smaller engine may even use more fuel because it takes longer to get up on plane. That is assuming it will even plane with a 6 cylinder. A 305 seems like marginal power for a boat that size.

 

You can get an honest 250 HP out of a 305 and they commonly produce 200 to 225 HP, which is more then enough on a fairly flat bottom or moderate V boat. I have a 185 HP 283 that pushes a 27' Chris Craft Sea Skiff to 37 knots. If that 26' cruiser of his is less then 2.5 ton, it'll do fine and still plane at 3 ton, though at the low end of the spectrum.

 

From what I've been able to find out there's not much difference between a car motor and a marine motor. I could get 350 to 400hp with a bit of work but I want to get some fuel economy out of it. Ease the old mans wallet. My first thought was to find a high hourse 4 cylnder in a car with fuel injection and swap it but I'm told I'd have unsolvable cooling problems. Any truth to this?

 

how did I post the same message twice????????

 

If you swap out a small displacement motor for a bigger one, you'll have gearing issues and you'll be asking a smaller motor to preform more work then the bigger one.

It's unlikely your hull will be able to handle a large HP increase, if it's of the typical shapes used in that era. In other words you could double the HP but net only a 10% increase in speed. It's nothing like a car.

You'll also have transmission to engine adapters to make up. How good a machinist and welder are you?

Instead of reinventing a wheel, who's dynamics you don't fully understand, you should just work with what you have or similar (SB Chevy setup). Boat engine operates much like drag car engines. They're either at idle or at full output (or very near this). They don't need to be flexible, just tough, much unlike a car which requires a very flexible engine in regard to output.

You could build a cooling system for a transplant if you want, but you don't even know what this might entail, so your best bet would be to stick with the pre-engineered stuff.

I'm not trying to insult you, but building custom engine adapters, cooling systems, etc. is just asking for more effort then necessary, particularly from a person who states, "I know very little about boats".

 

Par,
What does that Sea Skiff weigh all up?

 

Your biggest problem with injection would be the fuel map and the 02 sensor. Just get that baby running, fill it up with ice and beer and go. If you want better milage watch the throttle and change when the secondaries open if it is a 4 barrel. There are a $1000.00 to $2000.00 worth of marine parts to swap out, plus gearing and props. If you absolutely had to change motors I would use a long stroke 6. Even then don't do it, enjoy the summer!

 

My Sea Skiff a 3.5 ton (light) wooden lapstrake.

 

Frankly I would go with the

There are significant differences between marine and auto engines, almost none of which are visible to the naked eye. The carb is a marine carb ( the differences are internal) the manifolds are different. It probably has larger cooling water passages and uses marine exhaust risers with water injection. The starter and alternator are "marine". Again the differences are not obvious except the price. But auto electrical parts are not safe on a boat. see http://newboatbuilders.com/pages/fuel-2.html for more details. it probably also has a different cam set up.

So rather than fool with it, just give it an overhaul and get it running. After sitting that long you will need a carb rebuild kit, new gaskets, and a lot of other stuff.

By the way that 305 is a damned good engine , very strong, and was pretty much standard in much of the boating world so you shouldn't have any problem finding parts.

 

As Peter (and others) have mentioned there are substantial differences. Yes the cam is a different grind, carbs have visual clues that make them distinctly marine (look for the J shaped bowl vents), flame arrestors, etc.

You couldn't ask for a cheaper engine to rebuild, though I would completely disassemble this engine after this long a layup. Most of the time you'll have rusted cylinder walls and other issues, after this long lay up, to contend with. You could just toss a handful of parts at it and crank it up, but a good bit of damage will be done, like when those possibly rusted cylinders reject, the also probably rusted rings sliding by. Or the little bits of metal and rust that will find their way into the bearings once you do get it started.

 

PAR that information is why I'm here and not tearing into the unknown. I didn't figure the hull would handle a big increase in hp. I could build that kind of power with a sbc. I would be defeating my purpose for fuel economy.The trans and gearing issues I wouldn't of thought of. Losing 300lbs. of engine would of been nice. I'm hoping there's no rust damage in the cylinders and I knew a good tune up was in order. I've had good luck with other motors that have that long. Any tranny and or propeller issues I should look for?

 

It sounds like I'll be keeping the stock setup