4.3 to 5.7 swap

[gtfireftr]

Does anyone have an real life experience with swapping 4.3's to 5.7's.
SeaRay 290 DA....... I think it should be straight forward due to the fact that the boat came with that option of SBC..... I am aware outdrives are a different ratio...(1:47 I believe for ther 5.7)

TIA

 

[Rick Stephens]

Only real issue is 4 1/2 inches longer to the motor mounts on the side of the motor, and a 3 1/2 inch longer overall motor. Other than that it is just fiddly bits of hardware.

 

[gtfireftr]

Only real issue is 4 1/2 inches longer to the motor mounts on the side of the motor, and a 3 1/2 inch longer overall motor. Other than that it is just fiddly bits of hardware.

I assume that the mounts just lag into the stringers as with the 4.3 just 4 1/2 inches forward.....Rear mounts are the same....So everything else should fit?? Bell housing, coupler transom assy? Also will the throttle and shift cables bolt up the elbows as with the 4.3's ?
I am really considering this, but don't want to end up with a nightmare....

 

[Rick Stephens]

No nightmare. And how it mounts to the stringers depends on how your bilge is built. But yes, basically you need mount spots 4.5 inches ahead of where the 4.3L mounts are and a doghouse that is 4 or 5 inches longer than the the 4.3 uses.

Then you will need the different motor and different exhaust mani's. You may need some mods to the accessories hanging off the front. You don't say what year 4.3L you have, so kinda hard to advise what will cross over and which 5.7L you should aim for. There can be gotcha's here and there, but all are resolvable with a boat's worth of $$.

 

[gtfireftr]

No nightmare. And how it mounts to the stringers depends on how your bilge is built. But yes, basically you need mount spots 4.5 inches ahead of where the 4.3L mounts are and a doghouse that is 4 or 5 inches longer than the the 4.3 uses.

Then you will need the different motor and different exhaust mani's. You may need some mods to the accessories hanging off the front. You don't say what year 4.3L you have, so kinda hard to advise what will cross over and which 5.7L you should aim for. There can be gotcha's here and there, but all are resolvable with a boat's worth of $$.

the 4.3's are vortec, and fairly new... changed in 2017..... I am hoping that everything swaps over meaning the front accessories....I am looking at a vortec 5.7 roller cam.... my boat offered the sbc as an option, so I am confident it fits...
Thanks for the reply...

 

[Scott06]

I swaped a 4.3 for a 5.0 if youre boat was sold with a sbc if think you will find what I did- the needed 4&1/2” in front of the engine will be there and the stringers had a 12” long pad so that the 4.3 and sbc side motor mounts would both fit.

I bought a partial Engine package from Michigan motorz. https://www.michiganmotorz.com/vortec-marine-silver-package-1967-current-replacement-p-58.html

All my accessories front and rear swapped, as did the wiring harness, just got a 5.0 ignition module. The shift plate fit up to the exhaust elbow, just bought a merc throttle linkage Off the 357 alpha that fit my edlebrock carb. Reusing all components saved me a good chunk of change, but I was doing all the work. If you are paying someone to do it you are Money ahead to get complete bobtails.
I was able to keep my V6drive ratio just went a step upfrom 19” to 21” prop.

 

[nola mike]

My boat was offered with a 4.3 but did not have the mounts...

 

[gtfireftr]

I swaped a 4.3 for a 5.0 if youre boat was sold with a sbc if think you will find what I did- the needed 4&1/2” in front of the engine will be there and the stringers had a 12” long pad so that the 4.3 and sbc side motor mounts would both fit.

I bought a partial Engine package from Michigan motorz. https://www.michiganmotorz.com/vortec-marine-silver-package-1967-current-replacement-p-58.html

All my accessories front and rear swapped, as did the wiring harness, just got a 5.0 ignition module. The shift plate fit up to the exhaust elbow, just bought a merc throttle linkage Off the 357 alpha that fit my edlebrock carb. Reusing all components saved me a good chunk of change, but I was doing all the work. If you are paying someone to do it you are Money ahead to get complete bobtails.
I was able to keep my V6drive ratio just went a step upfrom 19” to 21” prop.

Thanks for the reply..... How was the performance with the new 5.0?

 

[Rick Stephens]

My boat was offered with a 4.3 but did not have the mounts...

As with mine.

 

[Scott06]

Thanks for the reply..... How was the performance with the new 5.0?

Fantastic.