got a question about a future V6 to V8 repower...

[Lou C]

OK seriously thinking of re-powering my old boat over next winter, from the 4.3 V6 to the 5.7 Vortec. Question is, the Cobra drive system I am using (I have a good original drive and a good spare) uses a 1:68:1 ratio. Will this work well with a V8 if I go to a larger pitch prop? I had used both a 15x17 and a 15.5x15 with the V6 to lessen the strain on the V6 since I think the boat is really a bit on the big/heavy size for the V6. Also, from some investigation it appears that you can't get new base 4.3 Vortecs any longer. Would like to start with new and it appears you can still get new 5.7s either Pre-Vortec or Vortec. Thoughts? if I go with a larger pitch prop will that gear ratio work out? OMC used 1.41:1 for the 5.7s, and a 1.50:1 for the 5.0s.
This boat was definitely available with the V8 from the factory and the engine mount pads are more than long enough. I know that keeping it with a V6 would be the least expensive option since less other stuff needs to be changed but if I'm doing it I would like to have the power the boat deserves.

 

[Bondo]

Ayuh,..... Considerin' yer now runnin' a prop at the bottom of the pitch range, It might run Ok with a prop at the top of the normal pitch range,....

One of those ole HiLiners I put together ran a V-6 ratio drive for awhile, with a 350,.....
It needed a 25" pitch to behave properly,.....

 

[achris]

Higher reduction and a larger prop is a good way to go. I have no problem with that, unless it pushes the prop beyond about 23", then you may run into problems (of finding a prop tall enough).

Chris.......

 

[Lou C]

Did some checking on the Michigan Prop website....
For a 23 pitch (3 blade alu) largest diameter is 14"...so not sure if that would work...
On the Cobra the lower gear ratios are all the same, any change is done in the upper, so if that didn't work I'd have to get a V-8 upper gear unit.

 

[Scott Danforth]

My searay had a 5.0, 1.62:1 and spinning a 15x19P stainless prop

While you could conceivably keep the cobra, only you can ask if its worth it

 

[Tail_Gunner]

What's type of boat? Actually length width and weight? Don't get caught up in diameter to much....at least ive never let that mean anything

This much I can tell you having a boat that pulls like a tractor (two cycle) from 30 to 50 is really a long term grin earner. Running at WOT not so much...and then there is chine walk and the ever pleasant recompension of your spine when at WOT.

Ohh well such is life...getting old that is.

 

[Lou C]

1988 Four Winns 200…20’9”, 7’8” beam 3800-4000 lbs est weight

 

[Scott06]

OK seriously thinking of re-powering my old boat over next winter, from the 4.3 V6 to the 5.7 Vortec. Question is, the Cobra drive system I am using (I have a good original drive and a good spare) uses a 1:68:1 ratio. Will this work well with a V8 if I go to a larger pitch prop? I had used both a 15x17 and a 15.5x15 with the V6 to lessen the strain on the V6 since I think the boat is really a bit on the big/heavy size for the V6. Also, from some investigation it appears that you can't get new base 4.3 Vortecs any longer. Would like to start with new and it appears you can still get new 5.7s either Pre-Vortec or Vortec. Thoughts? if I go with a larger pitch prop will that gear ratio work out? OMC used 1.41:1 for the 5.7s, and a 1.50:1 for the 5.0s.
This boat was definitely available with the V8 from the factory and the engine mount pads are more than long enough. I know that keeping it with a V6 would be the least expensive option since less other stuff needs to be changed but if I'm doing it I would like to have the power the boat deserves.

I did a 4.3 to 5.0 swap a few years ago in a Sea Ray 200 sport. If your engine compartment and stringers are set up for a V8 then it is pretty easy. I got a partial engine package from Michigan Motorz plus exhaust manifolds.

Since the 4.3 and 5.7 are essential the same block minus two cylinders I reused all my front and back accessories flywheel cover, coupler, wiring harness, fuel pump etc. Certainly had to buy a few items and spend some time in parts diagrams chasing down correct items.

I kept the V6 drive ratio (1.81) and stepped up from 19" to 21" prop. It would appear with merc drive ratios that each drive ratio step corresponds to about 2" in prop pitch.

At the time I stayed away from a 5.7 due to fears of having to replace the drive due to gearing (boat only had 37 hrs PO cracked the block). Knowing what I know now in terms of how the boat performs and the overall project cost I would have gone with 5.7 and probably been ok with a 23" prop.

At least you have a baseline with your boat. if you did the swap and kept your drive I would expect to need to go up 4" in pitch. Certainly a prop with bite like an Enertia or Revolution 4 would help tame the revs if needed.

Alternatively if you can find a prop to pulleys tear out that would also be a good option to upgrade everything

 

[Lou C]

Thanks yes I think ultimately it should work with my OMC because they used a taller drive ratio than Mercruiser used with the same engine. While I have 2 good 4.3 ratio Cobras I could see converting it over to a Volvo SX or even the SEI conversion. My thought process behind all this is that after weighing the boat it is much heavier than I thought (closer to 4,000 than 3,000) and the fact that I can still get a V8 brand new but it seems not possible with the V6.

 

[Tail_Gunner]

"I had used both a 15x17 and a 15.5x15 with the V6 to lessen the strain on the V6"

Based off that and your boat I doubt very much if you could swing a 21 on the setup. There is just not that tourqe difference between a 4.3/5.7

At the end of the day it's tourqe that swings props, and you have a heavy boat there. The 5.7 should compliment nicely.

 

[achris]

1988 Four Winns 200…20’9”, 7’8” beam 3800-4000 lbs est weight

My boat is definitely heavier than yours (I'm at 2,200kg), and yet my V6 performs brilliantly. The only characteristic a V8 would contribute is for it to be heavier in the a** end, and that's never a good look.

I've put my old V6 (1994 4.3LX) into a friend's 23' boat, to replace an aging V8, and the V6 out performed it in every department.

I would suggest you look a bit closer at your prop choices before going to the expense of an engine size upgrade. Unless you're looking for a 50 knot boat, then go the big block (or a stroked 5.7).

Chris.......

 

[QBhoy]

a GM v6 would have no problems powering a boat like that all day. I have had them in a 22 and a 23 foot cabin cruiser with no problems. If you did want to stick to a 4.3, you can get a vortec 220hp carb 4.3 from quicksilver, last I looked. Hope that helps.

 

[achris]

... you can get a vortec 220hp carb 4.3 from quicksilver, last I looked. Hope that helps.

Not for a few years now. Merc dropped GM like a hot brick when they finished with the cast iron blocks. Merc now offer a couple of flavours of their own recipe (and we all know how the 470 went )

4.5L - 200hp and 250hp (Merc's own engine)
6.2L - 300hp and 350hp (also Merc's own engine)

Chris.......

 

[QBhoy]

Not for a few years now. Merc dropped GM like a hot brick when they finished with the cast iron blocks. Merc now offer a couple of flavours of their own recipe (and we all know how the 470 went )

4.5L - 200hp and 250hp (Merc's own engine)
6.2L - 300hp and 350hp (also Merc's own engine)

Chris.......

cheers Chris...I think that quicksilver offered the GM 4.3 220 a good few years into the reign of the new in house engines. almost certain even early last year I saw them available. Could be wrong..I will have a look

 

[achris]

cheers Chris...I think that quicksilver offered the GM 4.3 220 a good few years into the reign of the new in house engines. almost certain even early last year I saw them available. Could be wrong..I will have a look

You might see it listed (as I also have), but it's not actually been available for about 3 years now.

 

[QBhoy]

Not for a few years now. Merc dropped GM like a hot brick when they finished with the cast iron blocks. Merc now offer a couple of flavours of their own recipe (and we all know how the 470 went )

4.5L - 200hp and 250hp (Merc's own engine)
6.2L - 300hp and 350hp (also Merc's own engine)

Chris.......

 

[Lou C]

See that is part of it, the only 4.3s you can find now are remanufactured not new. You can still get V8s brand new. If I could find one locally I might do that; vs buying a reman a distance away and then having to pay for shipping it back if there’s a problem. Might start researching engine builders here in Long Island to see if they’ll do a marine reman.

 

[Scott Danforth]

Fyi..... Based on my buds engine builder Mercs "new" 6.2 is old GM rotating assembly inside a mercruiser block casting. The crank/rods/pistons are GM bits

 

[Scott06]

See that is part of it, the only 4.3s you can find now are remanufactured not new. You can still get V8s brand new. If I could find one locally I might do that; vs buying a reman a distance away and then having to pay for shipping it back if there’s a problem. Might start researching engine builders here in Long Island to see if they’ll do a marine reman.

The 5.7 is the way to go. Hp diff between a vortec 4.3 and 5.7 is 225 vs 295, torque diff is 268 lb ft vs 370…and the torque curve for a 5.7 is flat http://marinepowerusa.com/wp-content/uploads/2019/08/57lspecs.pdf

if you are running a 17 now you d probably need a 21 with a 5.7

 

[Scott Danforth]

Lou.....build a 6.2