4.3's to 5.7's swap in 280 Sundancer

[dnsellers]

After the discussion in my last post, and the advice of several of you (Thanks!! by the way) I have made the decision to go ahead and swap the twin 4.3's with the 5.7's. I am ordering them tomorrow A.M. and they should arrive by Friday. The motors each will come with block, heads, intake manifold, oil pan, valve covers, timing chain cover, oilpump, and harmonic bal. All of the above delivered w/ no sales tax for 1350 each w/ one year warr. My question from you guys now: I know these engines are very similar in many ways, but I also know certain things will have to be changed/upgraded.<br /><br />1. My mechanic said the existing gears might handle the increased HP, but he thinks and sugests swapping them. He can pull the gears in mine and swap them out even, with no parts cost except for his labor, with another mechanic buddy of his for the proper gears.<br /><br />2. Will the 4 bbl Rochester carb on the 4.3's work on the new 5.7's? I'm thinking they should, but might need possible proper jets?<br /><br />3. I am ordering brand new exhaust manifolds and risers for the new engine.<br /><br />4. Will the new 8 cyl engine mounts locate correctly w/ the existing ones?? I have heard 2 sides to this story. The mounts are towards the front of the 4.3 on each side.<br /><br />5. I was told bellhouseing end everything should match up on these two motors. <br /><br />If anyone has any exp. with this particular swap, as I'm sure it is a pretty common thing, please advise. This project will be started in the next wek and a half or so. Also, which 5.7 should I go with?? It is an 1989 Sea Ray Sundancer 280, but I was told I can go with the older style 5.7 ( I can't remember if it was the one or two piece rear main) Once again, thanks for everyones advice here.

 

[newport dave]

Re: 4.3's to 5.7's swap in 280 Sundancer

I havn't done a swap like that, but you may want to consider getting the 3" or 6" riser extensions (whatever clearance will allow) with the new manifolds and risers.<br /><br />Dave

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

Is there a benefit to having higher risers??

 

[rodbolt]

Re: 4.3's to 5.7's swap in 280 Sundancer

hello<br /> you will need the correct fly wheels.<br /> the mounts should line up. check the jet sizes for the 4.3 and the 5.7. what ratio is your current uppers? I think all the lowers were the same. it will require a major overhaul of each upper. what is the name of the shop doing the gear work? if ya dont mind me asking.<br />all the gears were pretty much the same as far as handling HP. its the final drive ratio that changes. make sure they can turn at least 4500 at wot or you will be suprised how fast a valve will suck through.

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

I'd never mind ya asking rodbolt..I see your in Kitty Hawk. I've taken many a trips your direction. Actually it isn't a shop per say. My best friend is a simple deckhand aboard a 110' ocean going tug. Well in the last couple years he has made good friends with the head engineer on board. Granted he primarily speacialized in diesels and gensets etc...he is fully certified and has a lot of knowledge on the smaller crafts ( two of which are his own). My other mechanic is "A-1 Mobile Mechanic" out of Virginia Beach here. Now granted he is mobile, but he has an awesome reputation in this area and has done several jobs on each of my other 2 boats. I trust his judgement. But then again rodbolt, I have read a ton of your postings. What do you think??? Should I have even gone this 4.3 to 5.7 route in the first place??? I think you posted on my earlier question about the same boat? <br /><br />Derek

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

By the way, you mention a valve sucking through?? Which valve and sucking through where?

 

[newport dave]

Re: 4.3's to 5.7's swap in 280 Sundancer

Derek,<br /><br />The higher risers will help prevent water from getting into your new engines. The increased weight of the 5.7's may raise the waterline a bit, so the increased height may be needed. Unfortunatly, you won't really know until you can take measurements with the engines installed and fully dressed and the boat is in the water. The additional height is always good, and it can't hurt anything (just your budget).<br /><br />Dave

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

I hear ya, and thanks for the feedback. The boat is 32' LOA, weighing in at almost 10,000 pound with a 10' 6" beam. I dont think the few extra pounds will raise the waterline too much, but I agree. I think the difference in price was 30 or 40 dollars per side for 3 or 4 extra inches. The engine compartment is huge, so I will def. take all that into consideration!

 

[piratedude]

Re: 4.3's to 5.7's swap in 280 Sundancer

derek-where did you get 5.7 motors for $1350?

 

[WillyBWright]

Re: 4.3's to 5.7's swap in 280 Sundancer

The mounts will have to be moved forward a bit. Most of the things that bolt onto a 4.3 will fit right up to a 5.7 with some visibly obvious exceptions. The 4.3 is basically a 5.7 with 2 fewer cylinders.<br /><br />I'd leave the drives alone, except I would strongly advise new water pumps (go ahead and reuse the circulation pumps on the front of the motors). New motors, new water supply pumps ... Always! For a big boat, I like the gear ratio you already have. MerCruiser packages based on motor and drive alone. That's stupid! The same exact package on a 19 foot skiboat as for a 28 foot Cruiser? Gimme a break! Bigger vehicles with the same motor have different ratios, so should boats! Those drives are fine just the way they are. You'll probably need steeper props, but changing props is a fraction of the cost of changing gears.<br /><br />Carb jetting should be close. Check the jet sizes for a 5.7, but I'll bet they're awfully close since the cylinders and pistons are the same, just more of them.<br /><br />The distributors will work, but you'll need new caps and rotors for a V-8, plus new wires. On Thunderbolt IV ignitions, there are different modules for different motor classes. Those should be replaced as well. They are mounted to a triangular-shaped base and mounted to one of the exhaust elbows. Those control timing advance and different motors have different requirements.

 

[rodbolt]

Re: 4.3's to 5.7's swap in 280 Sundancer

I am kinda with willy. I would try the original ratios before swapping anything on the drives.<br />when I was working in norfolk there was a A-1 mobile that messed up everything they touched. ask malcom at sandy point bait and tackle about any body else doing work. he still has a bunch of stuff done for people.on the distributors. the body will fit but it will require to many mods to work. may be cheaper to find the marine delco EST system. the complete v8 kit is about 200 each and come with cap coil and wires.<br />as mercrusier used this set up the system can be made compatible with the shift cut outs.<br /> you have a sled<br /> the lower gears may actually help. I would still rather see it with big blocks and bravo 3's

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

Well the A-1 I'm dealing with is a one person show, and almost every boater I have come accross who has had repairs done by him or knows someone hwo has speak very highly of his prices and workmanship. Rodbolt, possibly the same guy w/ many more years experience now?? Who knows. <br /><br />The outdrives on this boat have to be tore down and re-sealed anyhow. Wouldn't that be the best time to swap them if it needed to be?? I think that would save me from having to pay for it twice.

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

<br />I'd leave the drives alone, except I would strongly advise new water pumps (go ahead and reuse the circulation pumps on the front of the motors). New motors, new water supply pumps ... Always! <br /><br />SO willy, you're saying the water pumps on the front of the engines should be okay to reuse? I was thinking since they only cost about 60 bucks on eBay, grab a couple new ones and not risk a failure there. Also I'm considering going fresh water cooled on these new engines. I have come accress new ones for around 399 per system. Is this worth it? Should I go full system or half, and what is the difference?<br /><br />And lastly, and most importantly since I'm ordering the motors in a few hours. Is it okay to go with the pre-1987 style 5.7L, even though the boat is an 1989. Should the drives still bolt up?

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

Hey poi9jkl, email me at dnsellers2000@yahoo.com, I will rpely with all the details.

 

[WillyBWright]

Re: 4.3's to 5.7's swap in 280 Sundancer

If you're going to closed cooling, change them. You want to get rid of all the internally rusted parts. Otherwise it's optional. If you'd feel better about it, by all means replace them. Not quite sure about that nomenclature, but I'd bet full systems include antifreeze in the manifolds and half systems don't. If you want to go that route, no better time than right now. If you're in saltwater, you want closed cooling!<br /><br />I should mention that I was involved in such an upgrade. The boat experienced cooling problems and we had to use motor mounted pumps (like on a Bravo) and thru-hull intakes to supply enough water to the heat exchanger. The pumps in the drives were left in to cool them, but capped off at the transom and the connecting hoses removed.<br /><br />Make sure the motors and the pumps you are buying are suitable for marine use. Car stuff won't last.

 

[Bondo]

Re: 4.3's to 5.7's swap in 280 Sundancer

And lastly, and most importantly since I'm ordering the motors in a few hours. Is it okay to go with the pre-1987 style 5.7L, even though the boat is an 1989. Should the drives still bolt up?

I'm Guessing that you can get the 2 pc. rear main seal block motors Cheaper ???????<br /><br />You've got a 1 pc. now.....<br /><br />Not that it really matters......<br />You'll need Different Flywheels...... The Balance is different on the 4.3...<br />The Most Important Issue will be getting the Same Diameter as you have Now...... Then you can reuse your starters.....And, that means you need to check,+ Make Sure the New Blocks will accept the bolt pattern(str8 accross for the 12" flywheel,+ Staggered for the 14" wheel) of your starters.....<br /><br />It would be Nice if you could get the Old Out, before you start throwing money at it........<br />It's Better to Know what parts you need Before, rather than later........<br />With the Chevy/Mercruisers there's Always a "Work Around" to get things put together..........<br />It's just alot Easier to start with parts that Do Fit Right.............<br /><br />Your getting a Pretty Fair Price for those Long Blocks......<br /><br />I agree with your local Wrench on #1.... It's Only 2" of prop pitch to get back where you are now..... <br />I'd Water Test before I swapped the Gears.....<br /><br />#2, Rochesters can be Tuned to do a Good Job.....<br />But, I'm in Love with the Merc./Weber/Carter/Edlebrock AFB Carb........ <br /><br />#3 Ayuh,......... You've got No Choice...... <br /><br />#4 I Believe they're in the Same Holes......<br />In Your Boat, I'd think that the Worst it would mean, is a couple of new holes drilled into the stringers...........<br /><br />#5 Ayuh,...... The Bellhousing of the motor block is the Same, But, I've tryed to outline Some of the Issues you Might run into, above........<br /><br />Closed Cooling is the Only Way to Go, in the Salt..............<br />Go for the Full System, It'll Save the extra cost the 1st time you Don't have to buy New Manifolds..............<br />Taller Risers might also be a Good Idea...... Long's ya got the Space........<br /><br />It Sounds like you've got a Really Nice Ship....... You'll be Happy that you got the 350s.......

 

[Don S]

Re: 4.3's to 5.7's swap in 280 Sundancer

Is that marine engines you are getting or automotive engines. All cams are not created equal you know.

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

Hey Bondo, that was the detailed kind of answer I was looking for. Appreciated. I did go ahead tho and order the 87+ model, just a hundred bucks more, and it more matches the model year of the boat, if that even matters. Thanks for everyones info!!! Keep the replies coming with comments/suggestions as you think of them!! I check this post and forum several times a day, and the advice is very helpful as I go through my FIRST boat project.

 

[dnsellers]

Re: 4.3's to 5.7's swap in 280 Sundancer

Hey Don, they are full marine engines, a/ all new internals, cam, and roller rockers/lifters (one of those) Good looking out though.

 

[16Pilot]

Re: 4.3's to 5.7's swap in 280 Sundancer

You had better consider a larger fuel tank !!LOL!! That's pretty cool that you are stepping up. So many people have talked about it(I am guilty) but it will be neat to see the outcome. The one thing really concerns me is the outdrive gears. Oh and why not pay $120.00 for two water pumps? you just put out 2800, whats another 120.(See DonS's tag line) When I rebuilt my 4.3 I considered a 5.7 instead. I didnt have the testicles or resources to try it though. Good Luck to ya and I hope they sound sweet.<br />P.S. Why not just go through stern exhaust? That would be all of it.