Mercruiser 5.7 repower options - the day has come

[Devil_Inside]

Well, it finally happened. My 1995 (pre-Vortec) Mercruiser TBI gave up the ghost yesterday, right in the middle of our short boating season. Not a huge surprise considering it was a 24 year old raw water cooled motor with approximately 1100 hours on it.

The question now is what to do next? I am analyzing (probably over-analyzing) all the different options, trying to figure out time vs $$$ vs keeping my sanity. Do I go buy a complete drop in (not likely considering the $, but still an option nonetheless)? Do I hunt for a used motor (or an inexpensive boat with one in it)? Do I go the long block route? If I go with a long block, what other crap I will have to buy to go along with it, and what would it all cost in the end?

This forum has always steered me in the right direction so I am very interested in hearing your advice and suggestion. I am especially interested hearing from people who have gone through this already. Also, if you know where I might be able to find a good used engine, or anyone with a good price on long blocks or complete engines please let me know. Everything is on the table right now.

 

[Yegboats]

Great question. Any chance you got your serial number?

 

[Scott Danforth]

1100 hours is low hours for an SBC. are you sure the motor is toast? normally with proper maintenance, 3000-4000 hours is the norm.

not sure of your wrench turning skills, however the cost of a 5.0, 5.7, or 6.2 as a motor is about the same

however if you want to keep the TBI setup, then like-for-like displacement long-block swap

a rebuild of a small-block from your local machine shop will be in the $1500-$1800 range
you can buy a GMPP block, a SCAT/K&B rotating assembly, a complete cam and valve train kit, and new cylinder heads in the $3500 range

your local GM dealer will also have long-blocks

however prior to spending money, I would pull your motor and go over it to determine what the issue is.

 

[kenny nunez]

In addition to Scott’s suggestion check with Marine Power in Ponchatoula, La. 985 386 2081

 

[Devil_Inside]

1100 hours is low hours for an SBC. are you sure the motor is toast? normally with proper maintenance, 3000-4000 hours is the norm.

not sure of your wrench turning skills, however the cost of a 5.0, 5.7, or 6.2 as a motor is about the same

however if you want to keep the TBI setup, then like-for-like displacement long-block swap

a rebuild of a small-block from your local machine shop will be in the $1500-$1800 range
you can buy a GMPP block, a SCAT/K&B rotating assembly, a complete cam and valve train kit, and new cylinder heads in the $3500 range

your local GM dealer will also have long-blocks

however prior to spending money, I would pull your motor and go over it to determine what the issue is.

The motor hydrolocked. Upon inspection I discovered water intrusion in all four cylinders on the starboard side only; port side was fine. A little bit of “milkshake” visible under the valve cover on the starboard side, the oil in the pan looks fine and at the correct level. The exhaust manifolds and risers (OEM) were new as of this season, so I am guessing a cracked head or bad head gasket....not sure what else it could possibly be. I haven't pulled the head yet, but I am plan on doing so after I remove it from the boat because I want to determine with certainty what caused the failure. One thing is for certain, it wasn't lack of maintenance or proper care...

The motor can possibly be saved, however considering it's age, and the cost of a rebuild, I personally think a new long block is the way to go. Possibly a reman, but leaning towards new. I called several places and the going rate for a new, pre-Vortec, base block with roller cam/lifters appears to be ~$2900. The re-man version is about $2300. I am not sure if going through GM would be cheaper, and I also don't know what (if any) parts would have to be swapped over - I remember reading something about marine cams, marine head gaskets, bronze "freeze plugs", etc but I could be mistaken.

 

[Scott Danforth]

I would pressure test the block, however if it is only on one side, my first place to look would be the manifolds

If your going new, go vortec. ($90 more)

so much better flow wise (power wise). you will need a new intake.

if you are leaning new..... your two choices for GM are GM dealers or the GM Performance Parts line. otherwise there are the aftermarket block suppliers

If I was going to spend $2900 for a long block, I would not buy a GM long block, however assemble it myself.

I would buy a GM PP block, a new set of GM vortec heads and a Scat/KB rotating assembly and build a 377 stroker with better parts for about the same money and have about 380-450hp available. granted you have to ditch the TBI

 

[Devil_Inside]

I would love to go vortec however, wouldn't this also require me to ditch the TBI? Alternatively I have heard that there are companies in AZ and CA that can flash my ECM, but I am not too familiar about the process.

Building an engine sounds fun and it is something that I have always wanted to do, so definitely something to consider.

Btw does anyone know what is the difference between the Mercruiser/Quicksilver long blocks vs let's say Michigan Motorz, etc. I can't figure out why the Merc/Quicksilver long block costs over $4k

 

[garbageguy]

Long block..

I'm on 3rd season of that done for a carb'd GM 5.7 in 1998 25 ft small cruiser. Sure, we had some hiccups, but pretty glad we did it that way. Had some unique circumstances as my son was a budding marine mechanic being taught by a seasoned marine mechanic using shop very close to us. Source of long block was local machine shop wanting to get rid of it b/c they were going to all-diesel work.

 

[porscheguy]

I called several places and the going rate for a new, pre-Vortec, base block with roller cam/lifters appears to be ~$2900. The re-man version is about $2300. I am not sure if going through GM would be cheaper, and I also don't know what (if any) parts would have to be swapped over - I remember reading something about marine cams, marine head gaskets, bronze "freeze plugs", etc but I could be mistaken.

A brand new exact replacement base engine from Michigan Motorz is $2900. It will have proper head gaskets, cam, freeze plugs, etc. IMO it’s worth the extra $600 to eliminate the guesswork and need to partially tear down a brand new engine so you can make it marine suitable. And it will include a brand new circulation pump.

a brand new vortec base engine with roller cam is $90 more. But the only cost effective way to make it work is to find a donor engine That’s ruined but with all accessories, wiring, ignition, etc still intact. This obviously adds more expense, and is dependent on availability. If I went this route I’d look for a donor with MPI or a 4 barrel. I would understand the reluctance to switch from fuel injection to a carb, but the TBI barely qualifies as fuel injection. In addition, a carb fed by an electric fuel pump starts almost as easily as FI.

one thing you didn’t mention is your outdrive. Alpha or Bravo? If an alpha, keep things fairly stock. There’s no reason to spend the money on a 400hp stroker if you’ve got to nurse it along gently so you don’t trash the drive.

 

[hnt]

I converted my 1996 5.7LX EFI to a Vortec motor which made it into a 5.7LX EFI Gen+. Went from 250hp to 280hp. This the TBI set up with a low pressure fuel pump feeding the VST

In 1996 the 250hp model used the 880 casting block but the non-vortec heads (story is that the heads were not ready) half way through the model year they started using the Vortec heads (Gen+). I went through each part number for all engine parts on both models by serial number and found out the only difference was the heads and the intake manifold. The ECU even was the exact same part number (same programming). I bought a set of rebuilt Vortec heads and new cast iron marine Vortec intake manifold online and made the switch. I picked up 30hp for a total cost of about $750 and went from a 22P propset to a 24 propset with the same WOT rpm with my Bravo III. I picked up 3.5mph top speed and 3mph at cruise with the same rpm which translated to about a 15% increase in mpg.

I can give you more information if you are interested.

 

[Rick Stephens]

If yer gonna stay TBI, build a SCAT stroker and enjoy! I'm with Scott there, pressure test, decide whther to buy a new block or rebuild your own. Too many things to change to go Vortec.

 

[Devil_Inside]

I found a used 5.7 Horizon MPI FWC engine with ~500 hours for $3500 locally. The engine was coupled to a Bravo drive so it's already setup with everything I need... I think that's the route I am going to take. Hopefully I am making the right decision.

 

[Rick Stephens]

Wow.... what could I do with $3500 in my engine compartment?......my first thought would not have been a used motor. That's me though. Whatever floats your boat again.

 

[kenny nunez]

If you use this engine be sure to add a through hull fitting with a sea ****, the drive pump will not supply enough water to keep the engine cool as the engine will pull a vacuum from the drive pump and run dry. Then the Gaurdian kicks in.
You can connect the drive pump out put to the through hull suction line. Good luck.

 

[porscheguy]

I found a used 5.7 Horizon MPI FWC engine with ~500 hours for $3500 locally. The engine was coupled to a Bravo drive so it's already setup with everything I need... I think that's the route I am going to take. Hopefully I am making the right decision.

Go for it. You’ll likely get a small bump in power/performance and fuel economy. Not everyone is comfortable building an engine from scratch. The swap should be plug and play simple.

 

[hnt]

It would great if the seller could run the engine for you on the ground. At least they should be able to rig power to the starter so you can do a compression check...That will tell you a lot about the health of the engine. You could also do a leakdown test on each cylinder to confirm compression. Then you just need the differential tester, an air compressor and a way to turn and hold the crankshaft at top dead center for each cylinder being tested. Regardless knowing you have good compression takes some mystery out of buying a used motor

Good luck!!

 

[Devil_Inside]

Wow.... what could I do with $3500 in my engine compartment?......my first thought would not have been a used motor. That's me though. Whatever floats your boat again.

The goal here is to get back on the water as soon as possible, as our season here in New England is pretty short as it is. My slip is already paid for the year, insurance is paid for the year, water tax is paid for the year, I go on and on. Building an engine is fun, and something that I absolutely would love to do one day, but I don't have the time right now and I am also not properly equipped with tools and knowledge.

 

[Devil_Inside]

If you use this engine be sure to add a through hull fitting with a sea ****, the drive pump will not supply enough water to keep the engine cool as the engine will pull a vacuum from the drive pump and run dry. Then the Gaurdian kicks in.
You can connect the drive pump out put to the through hull suction line. Good luck.

I will look into that, but the Bravo drive doesn't have an internal impeller, instead there is a belt-driven sea-water pump on the motor itself, which sucks water through the drive. Thank you.

 

[kenny nunez]

I would still add a through hull set up. This way there is no way you will ever have problems with any restrictions with the in coming supply. Several posters in the past mentioned problems with foreign material being found in the supply hose between the drive and gimbal housing. Fresh water needs everything you can give it. This would be a good time to inspect the raw water side of the cooler’s tubes by removing the end caps and blowing air through each tube.
This engine looks good, but what and why is it being replaced, did the seller say why? Always a good question.