a few questions for the boat and carb experts

[scoobert]

i was in the boat today, winterizing it the hard way seeing as how it froze before i could do it this year. i took off the two risers, also took off the one cracked exhaust manifold. the questions are this...

1. how hard is it to align the engine to the drive unit?
i have not taken the engine out, but i want to know how hard it would be to do a 350 swap.
2. can you just put a supercharger under a carb and call it a day? or do you need to fiddle with it? i have heard the term jetting before, dont mean anything to me really.
3. with the old 305's can you s/c them without other mods? this is a thunderbolt 4 model.
4. is there an easy power mod for them to gain hp without losing mpg?
5. how interchangable are 305/350 parts?

 

[SHU-DOG]

i was in the boat today, winterizing it the hard way seeing as how it froze before i could do it this year. i took off the two risers, also took off the one cracked exhaust manifold. the questions are this...

You may have some issues with the block freezing if the exhaust headers froze. Theck the freeze plugs and see if they are still in the block.

1. how hard is it to align the engine to the drive unit?
You need an lignment tool to start with. Not too hard just takes patience. A lot of washers may be necessary. But it should go in close to where you had it.... UNLESS it was not installed properley to begin with.
i have not taken the engine out, but i want to know how hard it would be to do a 350 swap.
2. can you just put a supercharger under a carb and call it a day? or do you need to fiddle with it?
Supercharger would go before the carb. Called a carb hat. Vorctec, paxton models. Others like Whipple, B&M, BDM sit on top of intake manifold(may need to change) and then your bigger carb sits on top of that. That is the cheapest way to go. A lot of used smaller superchargers on Ebay.
i have heard the term jetting before, dont mean anything to me really.
Jetting is simply a way to adjust the fuel for altitude, dial in, etc.
3. with the old 305's can you s/c them without other mods? this is a thunderbolt 4 model.
Do not know the Thunderbolt model. If it has forged internals yes. If not i wouldnt touch it.
4. is there an easy power mod for them to gain hp without losing mpg?
With the 305 probably not worth your time or money. Exhaust arent cheap, a cam, heads, etc are only going to give you minimal gains. I would purchase a built 350 or a crate motor to stick in there. You can find them all over the place. Try www.offshoreonly.com for a lot of info.
5. how interchangable are 305/350 parts?

Most of your externals will swap right over. A lot more available boat parts for the 350. Dont know about heads etc.

Hope that helps. More should pipe up shortly.

SHU

 

[FSTJACK]

i was in the boat today, winterizing it the hard way seeing as how it froze before i could do it this year. i took off the two risers, also took off the one cracked exhaust manifold. the questions are this...

1. how hard is it to align the engine to the drive unit?
i have not taken the engine out, but i want to know how hard it would be to do a 350 swap.
2. can you just put a supercharger under a carb and call it a day? or do you need to fiddle with it? i have heard the term jetting before, dont mean anything to me really.
3. with the old 305's can you s/c them without other mods? this is a thunderbolt 4 model.
4. is there an easy power mod for them to gain hp without losing mpg?
5. how interchangable are 305/350 parts?

Aligning the motor to the drive should probably be done by an experienced boat mechanic.

Anytime you supercharge a motor it must be within the limits of the motor or the motor must be upgraded to handle the increased loads. If you keep the boost at 4-5 lbs you will probable be ok on a stock motor. This is true of any motor. Some motors are built with stronger internals that can handle higher boost levels stock. Most marine motors are strong enough to handle 4-5 lbs of boost with no problems.
The ignition and carburation must be set up for a boosted motor. A new carburetor is probably in order to have the proper external signaling to the power circuit in the carb. Your distributor can be recurved for the blown motor if it has a mechanical advance mechanism. Most marine ignitions built in the last 15 years are all electronic advance so a different ignition system must be refitted.


There is no way to increase power output without increasing fuel consumption.

This is just a thumbnail and there are many many things to consider.

If your manifolds are broken your block might be broken also.

May be time to think about a trade in on another boat that meets your power needs.

 

[scoobert]

thinking about the trade. looking at many models. not sure just yet.

the waterjacket was cracked, took the engine out, welded it, put it back.
dumb boat mechanic never told me the manifold was cracked. i went back and told my welder he screwed up, just to find later it was not his fault, he never even saw the manifolds.

the boat could use a bit more to come onto plane. i like my nice steep pitch prop too much to change to a smaller one.

my other option is i have a 6.5 turbo diesel sitting idle. i could rebuilt it and gain 30%mpg.


there are two major things i dont like with this boat.
the gas tank is only 55 gallons, far too small for the long trips i take.
single engine, i don't feel safe going into blue water with only one engine.

if i go with one of my other large projects for next year i might have this boat for at least 3 more years. i need to enjoy it. see lots of 350's with 300hp (100 more then i have) for 2grand. wonder what kind of decrease i would see in mpg with the larger engine.
right now i feel as thou the boat is too large for 200hp, i swear i am not getting more then 1-1.5mpg.

 

[scoobert]

oh, if i swap a longblock in i can swap everything else? manifolds ect?

 

[SHU-DOG]

thinking about the trade. looking at many models. not sure just yet.

the waterjacket was cracked, took the engine out, welded it, put it back.
dumb boat mechanic never told me the manifold was cracked. i went back and told my welder he screwed up, just to find later it was not his fault, he never even saw the manifolds.

the boat could use a bit more to come onto plane. i like my nice steep pitch prop too much to change to a smaller one.

my other option is i have a 6.5 turbo diesel sitting idle. i could rebuilt it and gain 30%mpg.


there are two major things i dont like with this boat.
the gas tank is only 55 gallons, far too small for the long trips i take.
single engine, i don't feel safe going into blue water with only one engine.

if i go with one of my other large projects for next year i might have this boat for at least 3 more years. i need to enjoy it. see lots of 350's with 300hp (100 more then i have) for 2grand. wonder what kind of decrease i would see in mpg with the larger engine.
right now i feel as thou the boat is too large for 200hp, i swear i am not getting more then 1-1.5mpg.

Boats usually run on Gallons per hour.
Shit some of the big poker runners run on gallons per minute. LOL

 

[scoobert]

yeah i break it down to MPG because GPH could be max gph or minimum GPH
right now max GPH at about 30mph, is about 15ish. i have no flow rate meter on my boat. but at 15gph you can see why i hate having a 55 gallon tank.

 

[Scrambler1]

Sometimes boats get better mileage with a more powerful engine if the basis of that comparison is an underpowered set up which it sounds like yours is. Think about it from a load standpoint, smaller engine working harder for 30mph than the larger one. Also if the engine has extra power you have more room to play with the prop to get more mileage without killing your holeshot.

If longevity and reliability are important for long trips, especially offshore, stick with a non supercharged engine. Plenty of commercial offshore boats are singles, but you have to do a lot of preventative maintenance. Turbo diesels are entirely different but even with them you have to pay attention to how the boat is propped (have to be able to reach redline at normal load) and keep it below 80% engine load for cruising.

If you replace the engine move up to a mild 350. If you need more range or want to go diesel trade boats and find one that meets your needs.

 

[jerew65]

I'm sorry I'm late in responding. I'm an ex-marine service mechanic.

i was in the boat today, winterizing it the hard way seeing as how it froze before i could do it this year. i took off the two risers, also took off the one cracked exhaust manifold. (check everything to see if anything else is cracked) the questions are this...

1. how hard is it to align the engine to the drive unit?
i have not taken the engine out, but i want to know how hard it would be to do a 350 swap. Marine engines differ from automotive engines. Not wise to change to an auto engine. Alignment from the engine through the gib into the outer unit requires special tooling and knowledge.
2. can you just put a supercharger under a carb and call it a day? or do you need to fiddle with it? i have heard the term jetting before, dont mean anything to me really. Removing the flame arrestor or supressor system infavor of new carboration or FI could result in excessive gas fumes in the hull of the boat thus resulting in a better chance for explosion. It is unwise to modify the fuel system of a boat without seriously upgrading the ventilation system
3. with the old 305's can you s/c them without other mods? this is a thunderbolt 4 model.
4. is there an easy power mod for them to gain hp without losing mpg?Boats are rated at GPH. My 42" Fountain 3 screw at full throttle runs 108 GPH. Typically, a deep "V" with a min. 8' wetted surface for every 10 MPH gain you need an additional 100HP. Port match intake to heads, port and polish heads, cam change, compression change are good ways to increase power.
5. how interchangable are 305/350 parts?

 

[includemeout]

Find one of these and you won't worry about prop pitch

http://www.torqueshift.aeromarine.com/
and check this out

http://forums.iboats.com/showthread.php?t=207059

http://propulse.jetshop.se/

BTW, the only real difference in a marine 350( usually a truck engine) is the Stainless Steel head gaskets, fuel pump, distributer, starter, carb, and alternator ( all must be Certified for marine use)

Aligning the engine requires a manuel and the proper tool, not hard to do.