4.3LX repower?

[drun_trucker]

I finally found the boat that I love, the only problem is the mercruiser V6 pushing it. It's not bad but at 20' plus passengers it really is at it's performance limit.

Which brings me to where I am now. Do I repower the boat? I know a fair amount of what it will take to do such a thing, I'm looking at buying a junk boat with good engine and drive to swap, I'm looking at buying a nicer boat (18' range) that has a V8 in it and swapping my 4.3LX and drive out...then the real question is what do I gain?

I know the whole "No replacement for displacement" thing...yesterday I had 4 grown adults and two kids on the boat it launches okay and tops out at about 33 mph. I'd really like to hit closer to 40 at WOT and get up on plane with less effort. I hear that the 4.3LX is pretty damn good for what it is. Oh, I'm currently running a 4 blade 14.25x19 prop; 4600 rpm. (With that said, can I pitch up to 21* stay in the 4 blade and get closer to what I'm looking for?) Top end probably but I'm assuming my launch will REALLY suffer doing that?

So here are my thoughts: 1) If I can find a VERY VERY VERY good priced 5.0LX and drive swap them out: marginal gains at best 2) Find/buy a used 5.7 and drive or 3) Buy a brand new engine and matching drive

I obviously would like to spend the least amount possible. But like I said I love the boat. Being a 1991 Sea Ray it is almost show room condition. Floor, transom, upholstery ALL of it is MINT. "I" just want better engine performance. Please send me your thoughts.

One thing to keep in mind too is that I can sell the current engine and drive in the boat to offset some cost. I am the second owner of the boat and the first owner projects hours to be in the 300 to 350 range.

Thoughts and suggestions please.

Boat Specs
1991 Sea Ray 200
Mercruiser 4.3LX
Alpha1 GenII drive
4 blade 14.25x19 prop
WOT rpm 4600
WOT top speed 36mph

 

[Rick Stephens]

IMHO, you cannot prop up. Your performance would only suffer, not improve.

No way I would go with a 5.0L. Not enough gain for the pain.

Finding a donor boat with a 5.7 would be the way to go at this. Not that hard of a swap. Do some measuring now. Some things to look at - will the longer motor fit your engine cover or bay. Most likely as Sea Ray undoubtedly had a V8 as an option on a 20 foot boat. Here's a link to many of the dimensional drawings you'll need.

https://www.mercurymarine.com/en/us/documents/installation-drawings/

 

[alldodge]

I would suggest ditching the 4 blade and get a 21x3 blade. Four blades take more to turn (drag) and while they do provide more lift, lift isn't always a good thing.

 

[Howard Sterndrive]

how big is the fuel tank in the boat. you could put a 5.7 but unless you have 40 or 50 gal. tank, you will be watching that fuel gage the whole time.

 

[drun_trucker]

I have a full 6" of additional space to swap in a 5.7. I actually have JUST enough space to drop in a 454 but I don't think that would really be that necessary and totally overkill. I am however on the lookout for the donor boat. I have no intention of going MPI as I don't think the cost would be worth it. I have a really nice Holley 4bbl marine carb in the garage so I might be able to use that.

Bit my thought was to stay away from the 5.0. It seems like you guys would agree that the current configuration is basically maxing out the 4.3?

Let me know if you come across a good donor boat!? Please and thank you. Fuel tank I believe is 24 gallon. Not huge by any means, but the floor plan provides space for a fuel tank swap if it ever needed to happen.

 

[achris]

Something not right here.

Those numbers are way wrong. I had exactly the same engine in my (heavy for its size) 20 footer. My numbers were more like
Prop: 4 blade 14"x21" (Mercury "Offshore" series)
WOT RPM: 4900rpm
WOT Speed: 38 knots.

If I ran a 19" prop (3 or 4 blade) the revs were through the roof... BTW, as for 3 and 4 blade props. The balde area is roughly the same. Each blade of a 4 blade prop is smaller than each blade on a 3 blade prop. I prefer the 4 blade as they have a slightly better rake angle and are far less prone to 'weeding'...

A friend and I do runs across to a group of islands called Abrolhos (30nm each way). We run with 8 steel scuba tanks, the 180 litre under-floor tank full of fuel and 40 litres in plastic, plus Engel fridge and 2 days of food and gear. The boat still 'gets up and partys' even with that load. I have done the trip once with 3 PoB, 12 scuba tanks and gear, still no problems. That V6 should be a perfect fit for any 20 foot boat. 35 knots (40 mph) should be a 'walk in the park'....

I would recheck the revs (with a calibrated shop tacho) and speed (with a GPS).
If they still check out, then check the engine, compression and timing in particular, then make sure the carb is fully opening up and running properly. If that all checks out too, get the boat weighed, it may be water-logged.

I'd also like to know what your drive ratio is.

Chris..........

 

[drun_trucker]

I guess I'm not sure how to check the gear ratio on my drive. I can put a shop tach in and check RPM and use GPS to confirm speed. I'm swamped busy the next week or so but I will update as soon as I get that info.

 

[Scott06]

Gear ratio should be stamped on left side of drive under lube vent screw.

IF you like the boat I think it would be worth either the 5.0 or 5.7 swap.

I just repowered a 2004 Sea Ray 200 (that had a 190 hp 4.3 the previous owner cracked) with a 5.0. I stayed with a 5.0 because that was the largest engine offered from Sea Ray in that boat and I was worried that a Vortec 5.7 would be pushing the drive and maybe overpowering the boat. Also since this boat only had 38 hrs on it I wanted to not have to change the drive gears- with a 21" prop I'm at 4800-4900 rpm WOT.

I wanted to get a new engine so I purchased a 5.0 Silver partial engine from Michigan Mortorz- (stated 260 hp) and transferred all the accessories/ wiring harness and ignition off the old 4.3. Would be easier if you have a complete engine but if you can read a parts diagram not a big deal.

Bottom line it works great. Had 7 people in the boat and had no issue pulling a skier, tops out about 43-46 mph when I'm in the boat, plenty of power.

A 5.7 would work as well, and is the same money, so if you are looking used you could do either, but I definitely would have ended up needing to re-gear or swap the drive with a 5.7.

 

[Rick Stephens]

I guess I'm not sure how to check the gear ratio on my drive. I can put a shop tach in and check RPM and use GPS to confirm speed. I'm swamped busy the next week or so but I will update as soon as I get that info.

Agree with Scott on the gearing. I would bet your gear ratio says 1.84 stamped like he says. You could almost certainly use a 1.84 drive with a 5.0L, you could not with a 5.7. My issue with going a 5.0L is you can make your 4.3L V6 come darn near the same horsepower and spend a lot less money. With a pretty standard 1991 V6, dropping Vortec top end and decent intake you are looking at over 230 HP instead of the 190-200 you are currently. You would get more horsepower than the later model Vortec 4.3s because you don't have a balance shaft, which wastes around 15 HP in the newer motors. Vortec 4.3LX is rated at 230 HP. 5.0LX is rated at 260 HP. Lots more torque in the 5.0 though....

 

[Scott06]

Rick is right you can swap vortec heads, 8 bolt intake, and a 600 cfm edelbrock on your existing short block for a lot less and make similar power. If your compression and oil pressure are ok you don't need to pull the engine which is a lot less work.

 

[drun_trucker]

I got a 5.0LX. Got everything but the global housing, even got the drive for $1500. Sold just my 4.3LX and got to keep my drive for the same $1500.

Either way all I gotta do is build in New mounts then drop her in.

My next question is do I put my new Holley 650 on the replacement engine?

 

[Bondo]

My next question is do I put my new Holley 650 on the replacement engine?

Ayuh,... Merc don't run Holleys, never have, but it's yer barge, 'n you can do anything ya want to it,.....

 

[NHGuy]

If it's a marine Holley use it. if not don't. The marine carbs are safe and have the right fume control etc.
I think you will be happy with the V8. Lots more torque.
I hope you kept the drive for the 5.0, it has the right ratio so you can use common prop pitches. If not you will need tall props for the V6 gears.

 

[drun_trucker]

I have both drives. I lucked out, the part number for y-pipes on both applications is the same. No need to take that out when I pull the six on Monday. The Holley carb is a marine carb. I got it when I bought the new long block V6 (that I didn't need) when I replaced the engine on my older boat.

I also heard that I may need to keep the gear ratios from the V6 drive when I drop in the 5.0, somebody was telling me that it may need that gearing to keep the performance up. I intend to try the original drive (V6) and see what happens.

 

[Rick Stephens]

also heard that I may need to keep the gear ratios from the V6 drive when I drop in the 5.0, somebody was telling me that it may need that gearing to keep the performance up. I intend to try the original drive (V6) and see what happens.

That someone was wrong. Merc never ever shipped a 5.0L with a 1.84 drive on it. You can certainly prop up, but much easier to stay in primo propeller range with the 1.64 drive.

 

[drun_trucker]

That may have seemed or sounded funky. That someone didn't say that it shipped with that gearing. He said that he went that direction to get better performance out of the setup he had in his boat.

Im not one to say right or wrong, but I suppose if it works that's the most important.

 

[drun_trucker]

One quick question...does anybody know if the motor mounts are in same location? I haven't pulled the 4.3 out yet so I just don't know. I'm wondering if I have to plan on building in new mounting locations. I read in a different forum that a guy was doing the same swap and didn't need to change the mounts...I sure hope that is the case. I have the marine lumber and plenty of fiberglass, just would be super cool to swap motors in a half day.

 

[alldodge]

As I remember yes you need to move them. Rick Stephens just did the very thing going from V6 to V8

 

[Rick Stephens]

close to 4 inches longer for the V8.

Here's the drawings for the two motors.

https://mercurymarine-gsdesign1.net...6-8f43-0969b7209f39/50lefialpha_1996-2001.pdf


https://mercurymarine-gsdesign1.net...e-9186-4ce3dfaead13/43lefialpha_1996-2001.pdf

 

[drun_trucker]

Sea Ray put the mounting locations just a 1/2" short of necessary to get the V8 mounted.

However, the repower is complete. 305 ci V8 is in and test fired on muffs. Ran good from what I could tell. Tomorrow we drop it in the lake and see what happens. It literally was a drop in deal. Didn't even adjust the mounts, no need.