21' w/ blown 4.3l engine... swap options?

[dr.fowler]

Hey all, I have a 1992 or 1993 closed bow 21', and the engine blew on me this weekend. Water in the oil and almost no compression... anyway, I want to swap it out and get something in there with some real power, like an LT1 or LS1 engine. I know it would be a big job, but I wonder if there's anything that's more or less stock to swap in, or anything that would go in without too much of a fight. I've done motor swaps on cars, but this marine motor thing is completely new to me. Any advice would be greatly appreciated! Also, any links to reference material would be great too, I'm not finding much on the intarweb.

Thanks in advance!

 

[SpinnerBait_Nut]

Re: 21' w/ blown 4.3l engine... swap options?

Mercruiser/Volvo/OMC I/O and Iboard trouble and repairs.
When they get the problem with the forum fixed.

 

[tommays]

Re: 21' w/ blown 4.3l engine... swap options?

Anything other than the same year 4.3 (different flywheels ect ) will be a problem


The outdrive is geared for the power of the 4.3 a bigger motor you will not be able to take advantage of the extra power

Car motor cams grinds will suck in water



Tommays

 

[fourwinnsdook]

Re: 21' w/ blown 4.3l engine... swap options?

get a vortec 4.3 with a 4bbl carb. i think that would be the easiest way to get some extra horses without having to fabricate to much if any.

 

[superpop]

Re: 21' w/ blown 4.3l engine... swap options?

If you have the space and money you could swap in a 5.7L V8 of the same year along with a 4 barrel carb, that would give you more power. The manifolds will need to be replaced for sure along with the risers if they are in bad shape. Everything else should bolt up. a 4.3L is simply a 350 with the two front pistons shaved off. Get a 350 truck motor and swap out your marine parts. You will also need a marine distributor, the starter, alt, and most of the other tidbits should bolt up. You will need to regear the drive or get a really wacky prop to compensate for the differences in torque and HP.

 

[dr.fowler]

Re: 21' w/ blown 4.3l engine... swap options?

would it be faster to just get a matching drive for the 5.7l instead of messing with gearing? that's what we've been leaning toward

 

[riverjet502]

Re: 21' w/ blown 4.3l engine... swap options?

Just a thought here, why not just change props instead of changing gears? If your running lower gears you should be able to run a bigger dia prop or a prop with a lot more pitch especially with the torque of a bigger engine. I'd call Ron Hill (Hill Propellers) and see what he recommends for a prop for this application. Just my $.02 worth. With that size of boat I would consider a 383 stroker at minimum or prefferly a rat motor.

 

[fourwinnsdook]

Re: 21' w/ blown 4.3l engine... swap options?

the prop change is a thought, but i wonder what pitch you would have to run. it would have to be something crazy... well, i don't know. you are making alot more torque, but it's not a huge difference in rpms or HP really. Call Ron Hill and kep us posted. Good luck!

 

[Don S]

Re: 21' w/ blown 4.3l engine... swap options?

Changing props is not a good way to go. Props have to be in a certain pitch range to be effecient. Usually in the 17 to 21 pitch range. When you start going up higher than 21, you will start loosing your hole shot ability, and it will take longer to get to top speed, and the top speed will probably decrease also.
That is why OMC, Mercruiser, Volvo and any other outdrive manufacturer has different gear ratio's. If it wasn't necessary, they would have made them all the same.

 

[fourwinnsdook]

Re: 21' w/ blown 4.3l engine... swap options?

i'm no expert, but woudln't changing prop sizes be like changing tires size on your car? which is in tern changing gear ratios? i mean what if he went from a 21 pitch to a 17 pitch? that is probably a big enough jump to compensate for the ratio change, but it will probably put more strain on the drive components because of so much more pitch.

 

[tommays]

Re: 21' w/ blown 4.3l engine... swap options?

A 3.0 LX (135HP) WITH A 2:1 DRIVE can turn a 21" prop and push a 19' boat to 41 MPH


For what its worth the above boat was offered with a 3.0 , 4.3 and a 5.0 the 5.0 only got the boat up in the 50 MPH range with all that extra HP


When you double the HP with the V-8 you need the 1.5 ratio or you just NOT going to go faster



Tommays

 

[fourwinnsdook]

Re: 21' w/ blown 4.3l engine... swap options?

The diference beteeen the 3.0 and the 5.7 are much more than the 4.3 and the 5.7 however the only reason you can not go any faster is because 1) the engine will not push the prop faster 2) the prop/motor is at peak rpms. so if you were to make the engine have more hp it would take the prop to max rpm and get you going faster within reason. You may not get the true performance of the v8, but it will do better than the v6. also you will burn more gas. i'm sure that has a lot to do with the reason for ratios.
There has to be some sort of mathematical equation to figure prop size to gear ratio. So if you were to take the gear ratio and prop size from a similar boat with a V8 in it and input the V6 gear ratio it should tell you what equivilant prop size you would need. WHERE ARE ALL THE MATH PEOPLE????

 

[Don S]

Re: 21' w/ blown 4.3l engine... swap options?

There has to be some sort of mathematical equation to figure prop size to gear ratio. So if you were to take the gear ratio and prop size from a similar boat with a V8 in it and input the V6 gear ratio it should tell you what equivilant prop size you would need. WHERE ARE ALL THE MATH PEOPLE????

Probably over in the Prop Questions and Topics Forum

 

[dr.fowler]

Re: 21' w/ blown 4.3l engine... swap options?

wow, I'm a little lost with all that. Honestly, We're just going to regear the stern drive to the recommended gearing for the motor, and get a good matching prop. What I really need to know is what motor is going to be the easiest to swap into there, and where to source it from. Are marine motors the same as regular truck motors? If I get a new crate 5.7L engine from GM, will I be able to put it in, or are there a lot of different parts on it? I've heard that there are different parts to get it more finely balanced. Is there truth to that?

I do appreciate all the input!

 

[Tail_Gunner]

Re: 21' w/ blown 4.3l engine... swap options?

Bondo-o may be in here shortly and clear it up, but if you just build your 4.3, put on a good 4 barrel along with a manifold and some vortec head's it will probably push 220 hp maybe more. A 5.7 would get you maybe 275 cost big buck's (4000-5000) and get you 2-3 mph gain

 

[Bondo]

Re: 21' w/ blown 4.3l engine... swap options?

If I get a new crate 5.7L engine from GM, will I be able to put it in, or are there a lot of different parts on it?

Ayuh,.......... That's the rub on using a GM Goodwrench motor,..........
You don't have a Blown motor to use as a Donor.........

If you want V8 power,......
You need to buy a Plug & Play bobtail Marine drop-in motor.........
That'll give you Most of the parts you'll need for the swap........
Btw,.... The "L" series motors you mention,... will Not Fit in a Boat........

I think Don has explained the Gear Ratio Issue,......... Quite Clearly........

As noted several times,.... The 4.3l, with Vortec Heads,+ a 4bbl. is a Pretty Respectable powerplant........

 

[dr.fowler]

Re: 21' w/ blown 4.3l engine... swap options?

I think I've used a term that I didn't mean to... I don't know anything about L series motors, I'm too much of a newb, lol! What I was getting at is the 5.7 litre motor. I found a site that said that the same year boat came with an optional 5.7 litre. I wondered how difficult it would be to get that in there. It sounds like it's a pretty straight drop in, as the motor mounts and many other parts are the same. I'm really not trying to get any better mph, I want a better hole shot for pulling up some bigger skiiers (I'm 250lbs and 6'3" tall) and just for better acceleration overall. I've tried all different types of props and stuff, and just haven't been able to get what I want. I feel like this is the chance to get some real muscle under the "hood".

Alternately, can a nitrous system be used safely in a boat? I've got a ton of land-lubber motor experience, but I've never heard of it on a boat...

Thanks guys!

 

[Bondo]

Re: 21' w/ blown 4.3l engine... swap options?

Alternately, can a nitrous system be used safely in a boat? I've got a ton of land-lubber motor experience, but I've never heard of it on a boat...

Nope,...........

It would last for a Shot or 2............. Maybe............

 

[EricR]

Re: 21' w/ blown 4.3l engine... swap options?

You are looking at spending a lot of money for very little gain here. Go with the 4.3 Vortec. Cheapest and easiest thing to do.

 

[riverjet502]

Re: 21' w/ blown 4.3l engine... swap options?

Post your question over on ( hotboat.com) "under gear heads forum" You just have to ask yourself what you are willing to spend to get your desired results. It may be cheaper to trade boats to get the power you want. If you like the boat I would do a stroked mouse motor. A 383 will put a grin on your face and make a nice sleeper out of your ride. Pretty much a cake recipe anymore and very reliable. If your engine well has the room for 2 more cylinders. Do your homework.....