5.7 MerCruiser blown what can I replace it with

[Nextelbuddy]

So I finally got my 5.7 mercruiser engine running great past couple days full tune up oil change use Mercury oil 25w40 mercruiser oil filter engine was running great hitting about 49 mph at 4800 RPMs.

Today today out on the water I was running about 37 to 40 mph 4400 rpms and the engine blew and stopped. It was rod knock.I started the engine again it was knocking extremely bad and then it locked up and seized.

So so very bad ending to my Saturday unfortunately.

II want to replace the engine and I was hoping somebody could tell me what other compatible engines I could put into the boat and transfer all of the marine specific components onto.

It's it's a '96 mercruiser 5.7 not sure if it is vortec or not. It does have the center bolts and the valve covers but I also read online that that's not necessarily an indicator that they are vortec heads.

​​​​​​My serial number is 0F760044.but I don't know how to tell by the engine serial number if the engine is vortec or not.

Can can I upgrade to another 5.7 350 vortec engine or can I go with a larger engine?

A a buddy of mine has a 383 scat engine he pulled out of his 69 Camaro. I'm waiting to hear back and see how much he wants for it because it's sitting in his garage.

An any help is greatly appreciated

 

[Bondo]

Can can I upgrade to another 5.7 350 vortec engine or can I go with a larger engine?

A a buddy of mine has a 383 scat engine he pulled out of his 69 Camaro. I'm waiting to hear back and see how much he wants for it because it's sitting in his garage

Ayuh,..... To go to a Vortec 350, you'll need a new intake manifold,......
Vortec motors have no center bolts in the intake,....
Only larger motor would be a 383 stroker,....

I'm guessin' the cam in yer bud's motor will be to hot for a boat, so you'll needs to swap out the cam,......

 

[alldodge]

Intake
Vortec 4 bolts per side 8 total
Non-vortec 6 bolts per side 12 total

Being you have a carb motor, your options are more open, but (there is always a but) some items may not bolt up because the bolt holes have been moved. In any case you can place about any SBC including a 383 stroker, so long as your ready to change some items like alternator and power steering ump items

 

[Nextelbuddy]

Ayuh,..... To go to a Vortec 350, you'll need a new intake manifold,......
Vortec motors have no center bolts in the intake,....
Only larger motor would be a 383 stroker,....

I'm guessin' the cam in yer bud's motor will be to hot for a boat, so you'll needs to swap out the cam,......

I already have an edelbrock performer intake manifold so that should fit even on a vortec engine right?

May I ask why a cam would be too hot/aggressive for marine application? What would happen running an aggressive cam

 

[Nextelbuddy]

I found a Volvo Penta 5.7 GSi engine for 1300 locally. Since that's still a gm 350, could I get that engine and swap over my mercruiser parts and drop the engine into the boat?

If I get an Auto engine, i looked online and saw that non marine 350 engines do not have the mechanical fuel pump boss drilled out. Since I have a mechanical fuel pump, does this mean I can drill out and tap the boss if it's missing?

 

[nola mike]

A too hot cam will draw water into the engine. Also generally for high rpm, rather than low end torque which is what you want in a boat. You'll need an electric fuel pump. Should be able to use the VP if you swap everything over I would think, but I'll let others correct me if I'm wrong...

 

[Rick Stephens]

The way a cam makes more power is by virtue of added overlap of intake and exhaust valves. What this induces is water getting sucked in from the wet exhaust. Mike is also right, you need full torque from idle to wide open. Performance cams give extra power by jumping the high rpm curve at the expense of low end. Kind of like watching a pit crew push a 600 HP stock car to get it rolling.

 

[alldodge]

I found a Volvo Penta 5.7 GSi engine for 1300 locally. Since that's still a gm 350, could I get that engine and swap over my mercruiser parts and drop the engine into the boat?

Yes, but some things may need new brackets to bolt things up

Don't mess with a auto (car) motor unless it came out of a truck. If using a truck motor would need to replace core plugs with brass or stainless and new head gasket

 

[Nextelbuddy]

So I've been doing a lot of searching for engines and I decided that I would like to just get another 350 5.7 engine.

I know that my current engine is a non vortec engine as I counted the intake manifold bolts on my intake manifold and I have 12 intake manifold bolts in total and it looks like if it was a vortec engine I would only have eight bolts in total two in each corner.

I figured now is as good as any time to upgrade to a vortec engine. So I'm curious what would be involved to upgrade to a vortec engine besides the obvious of changing head gaskets, camshaft etc...

I was hoping that I could find a used well-documented vortec truck engine, if that's the case what I still be able to successfully transplant all of the marine specific parts from my non-vortec 5.7 besides the mechanical fuel pump which I read that I would just need to convert to an electric fuel pump at that point since the newer 350 5.7 engines do not have a mechanical fuel pump mounting boss drilled out.

I should be able to swap over my exhaust manifolds, starter, flywheel, drive coupler, all of the cooling components, all the accessory brackets and accessories, and the distributor? And I figure that I would just need to upgrade the carburetor to a marine grade carburetor like the Edelbrock 1409 as my Rochester four-barrel car would probably not fit onto a vortec intake manifold and my current Edelbrock performer intake manifold which is for a non vortec engine probably won't fit either onto a vortec engine.

Is there anything else I'm forgetting that anybody else can think of?


would I need to make sure that I find a vortec engine that has cast iron heads and not aluminum heads?

 

[alldodge]

No need to change cam if motor came from a truck. They should all have cast heads unless someone changed, but I would stick with cast in any case

 

[Scott Danforth]

switching from non-vortec to vortec means you need a vortec intake manifold.

you CAN NOT use your existing Edelbrock manifold.

you need an Edelbrock 2516 or similar marine intake manifold for vortec heads. https://www.summitracing.com/parts/edl-2516

you can use your existing carb.

I would build a motor myself. however reman 5.7's are cheap.

 

[Nextelbuddy]

No need to change cam if motor came from a truck. They should all have cast heads unless someone changed, but I would stick with cast in any case

switching from non-vortec to vortec means you need a vortec intake manifold.

you CAN NOT use your existing Edelbrock manifold.

you need an Edelbrock 2516 or similar marine intake manifold for vortec heads. https://www.summitracing.com/parts/edl-2516

you can use your existing carb.

I would build a motor myself. however reman 5.7's are cheap.

thanks so much i appreciate the advice guys

Yes i will make sure to get a truck 5.7 vortec engine if i go that route.


i did find someone selling a boat locally that had a complete 7.4 alpha 1 setup for less than 2k, i have read all about the issues with 7.4 engine tq and alpha 1 issues and thus being why 7.4 alpha 1 combos were very limited however i wouldn't mind the increase top end if it meant i would need to make sure to always ease into throttle and never go 100% WOT from stand still


if i did choose to go that route, besides the obvious other parts id need to source such as 7.4 specific intake manifold carb combo and flywheel, starter and drive coupler... I'm guessing i would also need to be concerned with engine alignment being grossly off as well? if i found another boat with a 7.4/aplha setup already then i could reuse transfer several parts over and reuse my 1.61:1 drive as well.

for my 5.7 i planned on taking pictures of the engine mounts and shims making sure when i put another 5.7 back in tat the mounts and shims would be exactly as they were then checking alignment and adjusting from there.

with the 7.4 i assume it wouldn't matter if i got the shims and mounts like they were because 7.4 engine placement would be now changed making engine alignment more difficult?

 

[alldodge]

Going to a big block the front mounts need to be moved further forward and out. Transom mount is of no ossue

 

[Nextelbuddy]

Going to a big block the front mounts need to be moved further forward and out. Transom mount is of no ossue

do you mean that the engine mount arms on the engine need to be moved to a different mounting location on the block or they need to be mounted to a different location on the stringers meaning modifying the stringers?

I know with BMWs I do a lot of engine swaps and several BMW engines have different combinations of threaded holes on the engine block so that you can mount engine arms in different locations depending on the chassis that's being mounted into.

 

[Scott Danforth]

I know with BMWs I do a lot of engine swaps and several BMW engines have different combinations of threaded holes on the engine block so that you can mount engine arms in different locations depending on the chassis that's being mounted into.

your comparing a highly engineered automobile with a piece of wood with fiberglass over it and a motor mount lag-bolted in place with an impact gun.

not only is the big block longer, the mounts go out wider.

you have to do work.

also, the BBC/Alpha combo was only for the 88/89 years, the warranty of the drives being torn up prevented that combo going forward. that drive also shares very little with your 1995/1996 drive. remember, the Alpha drives changed in 1991

your best bet if you want more power.

take your existing block to your local machine shop. prep the block for a 3.75" stroke crank. build a 383/387. source a set of used vortec heads (about $200 without the machine work done, about $400 after the machine work done). install a set of 9:1 LCQ style pistons

if you go cast crank then you are into an honest 350hp crank hp or 320 prop hp for about $2300-$2500 depending on the prep work your block needs.

 

[Nextelbuddy]

your comparing a highly engineered automobile with a piece of wood with fiberglass over it and a motor mount lag-bolted in place with an impact gun.

not only is the big block longer, the mounts go out wider.

you have to do work.

also, the BBC/Alpha combo was only for the 88/89 years, the warranty of the drives being torn up prevented that combo going forward. that drive also shares very little with your 1995/1996 drive. remember, the Alpha drives changed in 1991

your best bet if you want more power.

take your existing block to your local machine shop. prep the block for a 3.75" stroke crank. build a 383/387. source a set of used vortec heads (about $200 without the machine work done, about $400 after the machine work done). install a set of 9:1 LCQ style pistons

if you go cast crank then you are into an honest 350hp crank hp or 320 prop hp for about $2300-$2500 depending on the prep work your block needs.

Thanks a lot for the explanation I will stick with the 350 power plant because ideally I'm looking for something that's more drop in and ready to go which at this point I'm not really looking to rebuild my current engine either.

I I found locally a 1999 suburban 350 vortec engine with 120,000 mi with a video of the engine running before it was pulled. They're asking $900 for it.

Since it's from a suburban does that count that it comes from a truck and has an appropriate or acceptable camshaft profile?

And and besides swapping over all of my marine specific accessories like the manifolds alternator starter flywheel etc.

What else do I need to swap over do I need to also swap over my oil pan and pick up from my mercruiser motor to the truck engine?

Thank you very much for the help sorry for going on and on about something that should be something simple I just want to make sure I do all of my research as much as possible before I dive into this.

 

[alldodge]

Yes a Suburban is a truck and will work
Do swap the pan so you can use the dip stick tube to suck the oil out, and puts it in a better location most times

Intake should be fine so long as its a carb, but don't use the Sub carb, marine only

 

[Nextelbuddy]

Yes a Suburban is a truck and will work
Do swap the pan so you can use the dip stick tube to suck the oil out, and puts it in a better location most times

Intake should be fine so long as its a carb, but don't use the Sub carb, marine only

gotcha, given that it is a 99 truck engine then more than likely it is fuel injected so i would need to purchase a new intake manifold to bolt on a carb right? i cant bolt a carb to the current manifold that is on it?


i know you said and linked the edelbrock 2516 marine intake manifold.. its so expensive compared to the 2716 which is for auto applications.

do i have to use marine specific intake manifolds? no way to use an auto intake manifold and use a marine carb?

 

[alldodge]

You can get away with an auto intake so long as your in fresh water

Don't see being able to use the intake but could look

Suggest going to Offshore only and ask for a cast iron or other marine used intake in their wanted section. Can also look in the swap shop for them or even a motor

 

[Nextelbuddy]

You can get away with an auto intake so long as your in fresh water

Don't see being able to use the intake but could look

Suggest going to Offshore only and ask for a cast iron or other marine used intake in their wanted section. Can also look in the swap shop for them or even a motor

ok great, yes i'm definitely in fresh water, lake lanier in atlanta ga.

so the last piece of the puzzle then will be hopefully my flywheel and bellhousing and drive coupler will bolt to the 99 vortec engine with out issue as well as the thunderbolt V distributor system.

seems like now i just need:

- 99 vortec engine
- vortec carb intake manifold
- new manifold and riser gasket kit (ordered and delivered 2 days after engine blew)
- new thermostat kit (ordered and delivered 2 days after engine blew)
- exhaust flappers for the y pipe (ordered and delivered 2 days after engine blew)
- electric fuel pump conversion
- swap all engine mercruiser specific parts... starter, alternator, PS, hoses, manifolds/risers, valve covers, oil pan/pickup/dipstick tube, shift cable brackets, engine mounts

now the picture is starting to get a lot more clearer.