Rebuilding my 350 Mag, Need opinions

[lenoble22]

Hey Everyone,
Well I will start at the top, I boat a 89 Wellcraft Scarab Excell 21ft with the 350 mag in it. When testing the boat it ran perfect. So I bought the boat and the first time I took the boat out, not 20 mins later I put a rod through the side of the oil pan. So I went back to the previous owner and he felt bad that it took a crap right after I bought it so he decided to give me another 350 that he was building for his corvette. Well since the motor is out I want to make sure everythings done right and the right parts are used. I would like the build the motor a bit but i'm not looking at spending alot of money. I plan on using the cams, heads, intake from the 350 mag that went on me. I was just wondering if anyone had any ideas on the best parts to use or what combination of parts to use. Anything will be a help. The previous owner is gonna help me build and swap the motors out so any input is greaty appreciated. Thank You

 

[Bondo]

Re: Rebuilding my 350 Mag, Need opinions

so he decided to give me another 350 that he was building for his corvette.I plan on using the cams, heads, intake from the 350 mag that went on me. I was just wondering if anyone had any ideas on the best parts to use or what combination of parts to use.

Ayuh,....

You've got the 350 Mag parts,... But Exactly What was used to assemble the replacement motor,..??

I would like the build the motor a bit but i'm not looking at spending alot of money.

And That is an Oxymoron.... Hor$epower co$t$ Money,... Lot$ of Money....

 

[mtnrat]

Re: Rebuilding my 350 Mag, Need opinions

If you could give us rundown of what was used in the engine for the corvette you will likely get some good advice. An engine is a mix of matching and complementary parts that work together to reach a goal. The sum of the parts of a good build is greater than the parts added up separately. Usually what makes a good car engine does not make a good boat engine. You are in the position to take the parts you have and taylor them for marine use.

 

[CharlieB]

Re: Rebuilding my 350 Mag, Need opinions

We just about need model and serial # from BOTH engines in order to look up what parts were used in each.

Marine/industrial motors are generally built using truck/industrial block, often pounds heavier than standard HP automotive blocks.

Same with cranks, rods, and pistons.

Soft plugs are brass, water pump impellers, brass or stainless, cam shafts of less HP but more torque than 'standard' automotive.

Heavy stem valves capable of sustained high heat of full load operation.

Car engines don't last very well under the rigors of marine use.

Personally, if I had to run an automotive engine, I would start looking at a 350 that belongs in a 2 1/2 ton flatbed truck.

 

[wca_tim]

Re: Rebuilding my 350 Mag, Need opinions

give a run down of what you've got and see what people say...


Charlie, Are you sure about all that?

the 1989 350 mercruiser that I used as a starting point in my current engine build, was same casting number as car block, had standard auto heads (for 300 hp crate motor) on it and 2-bolt mains, hydraulic lifters cast crank, same number as car and truck cranks.

I think the assertion that marine engines are built a lot heavier from the factory is largely a myth - especially in more recent years.

the cams are different more aggressive on both lift and duration, higher horsepower and torque normally than standard auto, truck or rv. Same heads, block, crank, rods, pistons, etc... different freeze plugs and head gaskets, at least in the run of the mill mer cruiser engines

The builder that set up my 383 verified that and said that block was plenty strong for over 500 horsepower, if the engine was built right....

Just my experience...

We just about need model and serial # from BOTH engines in order to look up what parts were used in each.

Marine/industrial motors are generally built using truck/industrial block, often pounds heavier than standard HP automotive blocks.

Same with cranks, rods, and pistons.

Soft plugs are brass, water pump impellers, brass or stainless, cam shafts of less HP but more torque than 'standard' automotive.

Heavy stem valves capable of sustained high heat of full load operation.

Car engines don't last very well under the rigors of marine use.

Personally, if I had to run an automotive engine, I would start looking at a 350 that belongs in a 2 1/2 ton flatbed truck.

 

[Mkos1980]

Re: Rebuilding my 350 Mag, Need opinions

For a few bucks more you could get a set of stock 906 Vortec heads, ramjet /Mercruiser roller cam and Vortec intake and make awesome reliable power.

 

[lenoble22]

Re: Rebuilding my 350 Mag, Need opinions

So far nothing has been built or swaped yet, my 350 mag is still dead in the boat and the guy that I bought it from is going to get the 350 this weekend. But i will see if I can get the serial numbers from each engine today or tomorrow

 

[Bondo]

Re: Rebuilding my 350 Mag, Need opinions

and the guy that I bought it from is going to get the 350 this weekend.

Ayuh,.... That's the 1 you need a History on,... More so than the serial #s....

 

[lenoble22]

Re: Rebuilding my 350 Mag, Need opinions

The 350 that hes getting is a 1970 350, so tomorrow we are going to take out he 350 mag thats in the boat right now and tear it apart, I'm assuming that because it threw a rod we are not going to able to salvage the block, so pretty much that is what the donar 350 will primarlily be used for.

 

[wca_tim]

Re: Rebuilding my 350 Mag, Need opinions

uh... what year is the boat... it may not work...

 

[Mkos1980]

Re: Rebuilding my 350 Mag, Need opinions

Its an 89. I dont think it will bolt up being its setup for a 1 piece.

 

[wca_tim]

Re: Rebuilding my 350 Mag, Need opinions

sorry... when went back reading, missed it blatantly in the first post...

yea, 89 is one piece reae main seal and different crank. needs at minimum different flywheel and I think coupler. Bond-o will know off the top what all it takes. I know (from personal experience) that the earlier two-piece seal was much more prone to leak...

 

[Uraijit]

Re: Rebuilding my 350 Mag, Need opinions

Yeah, don't waste all that money and effort with the older block. Go get a post-'86 block, and build it with a truck or marine cam. The Vortec heads aren't a bad idea, but if you do that, you're going to have to get a different intake, and probably do some mods, if you're running a cam with more than .450 lift. Stock Vortec heads are NOT generally just a bolt-on mod.

You'll also have to use self-centering rockers, and center-bolt valve covers.

 

[J. Mark]

Re: Rebuilding my 350 Mag, Need opinions

One word of warning. It has always been my understanding that if you use the old cam you need to use the old lifters and keep them matched to the cam lobes in order to prevent excessive wear. I would not reuse a cam for this reason.

Tear the old one down, your block may or may not have damage.

 

[Uraijit]

Re: Rebuilding my 350 Mag, Need opinions

You can use an old cam with new lifters. You just have to break it in properly.

20 min. at 2000RPM or higher (it's got to vary the speeds a bit) just don't let it drop below 1500RPM.

 

[wca_tim]

Re: Rebuilding my 350 Mag, Need opinions

if the "new" engine is being built for another car, it should have NEW cam bearings and lifters. I would strongly recommend adding a NEW cam to the mix for the max 150 we're talking here...

that's IF you do wind up going with the older 2-piece rear main shortblock. Still need to know more about that set-up... a lot more...

if you don't plan to rag on this boat too awful much, you would most likely be best off to bite the bullet and buy a fresh reman shortblock or longblock and be done with it. Add a little more cam if you want to, but if a marine reman, the installed cam will get you pretty good performance.

In my experience, cobbled together messes usually wind up being more expensive than starting from scratch before all is said and done...

Paddling sucks unless you're in a kayak

 

[lenoble22]

Re: Rebuilding my 350 Mag, Need opinions

well we just got done pulling the engine, found out #6 cylinder rod broke and it did damage the block some. The donar 350's not gonna work because it was a 2pc rear main seal and a 4 bolt main and the 350 mag that was in the boat was a 1pc rear main seal and its a 2 bolt main. So right now we are going to pick up a block that will work. Oil was extremely milky with about 3 quarts in the oil pan alone and every cylinder had water in it. So we are starting fresh, i'm looking at getting a new 383 strocker crank, possibly a new cam...Right now the only thing i'm going to reuse is the heads and intake. I am not sure what the factory specs are on the cam but we are going to take it in to find out for sure. So thats where we sit right now.

 

[Uraijit]

Re: Rebuilding my 350 Mag, Need opinions

The mains don't matter. Get a 4-bolt if you can. The only thing you really need to worry about, though, is whether it's a 1-piece, or 2-piece main seal.

If the oil's milky, it's likely that you hydrolocked the engine, and that's why you threw a rod through the engine. You need to find out WHY it hydrolocked, before you install the new engine, or you'll soon be replacing that one as well.

While you've got things apart, do a pressure test of your exhaust manifolds and elbows. My money says your starboard riser and/or manifold has had it. The other one's probably not too far behind.

 

[lenoble22]

Re: Rebuilding my 350 Mag, Need opinions

Thats what we were figuring it was probally going to be, we will be pressure checking the exhaust manifolds this week

 

[lenoble22]

Re: Rebuilding my 350 Mag, Need opinions

Finally have an update on the boat. Took the heads in to see what we had. We thought we had 76cc heads but it turns out that they are 63cc heads which is great. Also the intake it a taller one which the Mercury guy said is a high performance intake manifold. Still planning on stroking it. We are still looking at different crank possibilities but we are kinda stuck on the pistons. We want to get a dished shaped piston but we are having difficulty finding the right ones that will keep the compression ratio down. If anyone knows of a good place to find some please let me know. As things come in I will post. Any questions and feedback/input is greatly appreciated. Thanks everyone