Can I put a 5.7 in a boat that has a 4.3 currently this is a 17ft cuddy cabin

[3ronny3]

I have a Sea Swirl 17 ft cuddy cabin 1989 and I would like to put a 5.7 in it. Has anyone done this?

 

[JonBrown]

I knew a few people that did that and I think it fits almost 100% in place. Make sure your drive can handle the torque, that is all you are really adding. I believe most say the only difference was the sound with through hull exhaust. and about 20% more fuel. But your horsepower isn't a huge gain per hour gallon of fuel. I think mercruiser rates their latest 5.7 at 300 hp. although in the late 90's it was more like 225 , your 4.3 should be about 170 ish... Just remember every horse gained costs you something. And don't use a car engine. Marine engines are a little different.

 

[3ronny3]

Thanks for the info

 

[JJBoatr]

An easier way to get more power out of your 4.3 would be to install a 4 bbl carb. That will bring your power up to the 200 area. This way you wouldn't be adding any extra weight to your boat that is in my opinion, a bit short for the weight of a V8. I would imagine the extra weight would cause it to porpoise almost instantly if you try to trim up at speed. And as a bonus, the 4.3 with a 4bbl will still drink less gas than the V8.

 

[talon8]

The gear ratio in the outdrive may be incorrect for the new engine.

 

[bruceb58]

Do you really have room in front of the engine for a 5.7L?

If there is nothing wrong with the present 4.3, replace the heads with Vortec heads. You will need a different intake manifold as well.

 

[jerryjerry05]

Like Bruce asked?? Room?
​Exhaust would need to be through hull.
Gear in drive would work with a prop change,but should be changed.
Motor mounts might need a change.

What model do you have?
The change over to 4bbl could be done but finding parts might be difficult?

 

[jimmbo]

An easier way to get more power out of your 4.3 would be to install a 4 bbl carb. That will bring your power up to the 200 area. This way you wouldn't be adding any extra weight to your boat that is in my opinion, a bit short for the weight of a V8. I would imagine the extra weight would cause it to porpoise almost instantly if you try to trim up at speed. And as a bonus, the 4.3 with a 4bbl will still drink less gas than the V8.

A 4.3 is not a big engine. Unless the 2bb is really small you aren't going to see much power increase. If you gain any power it will be at the top end and you may need to increase the pitch of the prop to prevent over reving. That will weaken your holeshot.

A 5.7 in a 17 ft is a bit much. I have a 5.7 in an 18.5 ft. It hass a 2bbl 500cfm Holley. It is a little small for 5.7, but it is perfect for a 5 liter. I did put a Holley 650 spreadbore on it, I had to go from a 20 in to 22in on the prop. It gained 6 mph putting me at 66mph. The tiny primaries minimized it but I lost some holeshot

 

[JJBoatr]

A 4.3 is not a big engine. Unless the 2bb is really small you aren't going to see much power increase. If you gain any power it will be at the top end and you may need to increase the pitch of the prop to prevent over reving. That will weaken your holeshot.

A 5.7 in a 17 ft is a bit much. I have a 5.7 in an 18.5 ft. It hass a 2bbl 500cfm Holley. It is a little small for 5.7, but it is perfect for a 5 liter. I did put a Holley 650 spreadbore on it, I had to go from a 20 in to 22in on the prop. It gained 6 mph putting me at 66mph. The tiny primaries minimized it but I lost some holeshot

Good info. True the 4.3 isn't a "big" engine compared to a V8 but it is big for a 6 cylinder and makes excellent torque. I'm sure you know, but it's a 5.7 with 2 cylinders missing. My cousin has a Mercruiser LX 4.3 in his 19ft Sea Ray and it has a 4bbl carb. My manual says his mill has 200hp at the crank. That puts it right on par with a 2bbl 305 V8 from the same Era which is early 90's. A 2 bbl 4.3 puts out 175 at the crank per the same manual. I wonder if a spread bore Q-jet would've helped you preserve your holeshot while still giving you the gains you were looking for. But the larger primaries would likely eat more fuel than the square bore.

 

[jimmbo]

A 4.3 putting out 200hp is going to have less Torque than a 5.0 putting out 200hp. In 2002(when my boat and engine were new) a FI 5.0 was rated at 260hp, the carbed(2bbl 500cfm) 5.7 was rated at 260hp. On the water my 5.7 blows away the 5 liters by a long shot.

As I said I did use a Holley 650 spreadbore and that it did preserve a lot of my torque with the bigger prop. With the smaller prop, the holeshot was better with the 650. At WOT the secondaries were not fully opened as a 5.7 @ 5000 rpm doesn't not require more than about 435 CFM. Before you say I had a 500 CFM 2bbl Holley on it, note that 2bbl and 4 bbl carbs are flow rated at different pressure drops. The 500 cfm 2bbl is really 1/2 of the Holley 3310 4bbl, which was rated at either 750 or 780 cfm(depending on what year of catalog) so the 2bbl, when flowed like a 4bbl, is about 380 cfm, a little too small for a 5.7. But it is just about perfect for a 5 liter turning 5000 rpm.

A 4.3@5000 rpm with 80% volumetric efficiency will use about 300 cfm.

Holley does make a small squarebore 390 cfm marine carb. I don't know too much about the Edelbrock carbs other than they used to be Carter carbs, and my experience with them was on Chrysler cars and trucks. You always carried a screwdriver to stick in the choke so it would start. The smallest Edelbrock carb is 500cfm

 

[jimmbo]

To the OP apologies for taking this form a bit off your original post.

I believe your 4.3 uses the larger(V6) series outdrive. It should be able to handle the extra torque of the 5.7, but as I mentioned earlier, a 5.7 in a 17ft is going to be handful and maybe even a bit dangerous as your hull might not be built sturdy enough in the transom and stringers for the same torque. Is there enough room in front for the extra length of the engine. If you do go ahead with it, the gear ratios might not be optimal for the V8. Going to a higher pitch prop isn't the best solution but it can work