marine 350

[vervepipes]

Is there anything special or different with a marine application 350?  I may get my hands on a used one that is spotless, doesnt look like it has a drop of oil leaking, and the best part, it's free!

[Captkaos]

depends on what year.

[vervepipes]

OK, I'll try to get more info and stampings tomorrow evening

[vervepipes]

so it turns out that after all it's a 1969 210HP 307, it is rated at higher HP than the stock '86 350 and it is in very clean shape, no drips or leaks.  Here's the info on it:

Outboard Marine Corp.(OMC) stern drive model TUFM-69B, serial number J0117532
Block casting 3956632, intake manifold 392 7184 GM5.

So now the question, in a week or two  when the owner's time is up and the engine is destined for the dump, would it be worth replacing my 280,000 Km 160 HP 350 with a 210 HP 307?  Either one will be mated to some headman 4 into 1 headers that I got at the pick n pull.  I believe that 307's only had 2 bolt mains, but this will be far from a 500HP race car so I'm not concerned with that.  Ideas?  I definately like the idea of having a different powerplant than normal, but I can feel the size of what's filling my pants shrinking when I think of the low displacement for a crew cab lol

Ideas?

[Stewart G Griffin]

The good thing about these trucks (what yr is yours? The older the better/easier.....) is that smallblock engines can be swapped in and out with no big deal.  Maybe 8 hours or less depending on year of truck.  i wouldn't replace the 350 until it stops running.  But that's just me.

i think the smallest engines installed in crew cabs was 292 so........

[jdl71]

I thought the marine engines were reverse rotation.

[vervepipes]

I know in the 70's the rating changed from gross HP to net, but would that really account for 50HP difference between a 307 and 350?  the internals are not going to be changed at all, so build up for max power is no issue, it will be stock-ish with only headers and if I can find  one cheap used, an intake manifold.

[autorepr]

Go for it. I would just be concerned about rust and mud setimate in the bottom of the water jacket. To cool the engine in the boat the lake/river water is sucked up and pumped thru the engine then out thru the exhaust. Silt falls and collects in the bottom of the jacket so you may end up with it coming loose and collecting in the radiator plugging it up and giving you overheating issues.  Also the freeze plugs may have rusted thin since it's just water in there.  I'd knock out the freeze plugs and blast out the water jackets and install new plugs before putting it in. It may head off a problem later and it'llbe harder to replace the freeze plugs then. As far as reverse rotation... I think all you would need to do is change the camshaft?

[vervepipes]

Some boats use a heat exchanger though, where a separate water reserve is used for the radiator and the heat is exchanged through lake water

[Big Katz]

The 3 biggest differences between marine and automotive engines. They are the exhaust vales, camshaft, and compression. A marine engines use either SS or sodium filled vales. The camshaft grind is different for marine, I don't know the exact difference but you may not even notice the difference from a stock automotive cam. And marine engines tend to run lower compression ratio's ( 8/8.5 to 1 is common)to prevent detonation and high heat. I would install a new cam shaft and lifters, and make sure and check the rod and main bearings. Boats that are ran hard tend to eat up the bearings. Better to check it on a engine stand than after it is in the truck with oil dripping on you!

[bobcooter]

Something to keep in mind. 307 parts are not that plentiful and they generally cost more than 305/350 parts when you can find. If you just want a free engine to run until it dies, I say go for it. If you want to make some mods, like cams and things, I would reconsider. Look through Summit and Jegs catalogs for 307 parts. Hardly any that I remember. Just  sayin...

[bake74]

Something to keep in mind. 307 parts are not that plentiful and they generally cost more than 305/350 parts when you can find. If you just want a free engine to run until it dies, I say go for it. If you want to make some mods, like cams and things, I would reconsider. Look through Summit and Jegs catalogs for 307 parts. Hardly any that I remember. Just  sayin...

     That is a very good point, they stopped making the 307 I believe in the late 60/ early 70's.  Parts might be hard to find unless a 305/350 parts will swap.

[vervepipes]

That would be the point, a drop in engine needing only new head, thermostat and water pump gaskets (to make sure they are glycol compatible) to run until I can find a 454, I would not change any of the internals.  The 350 in my truck is quite a leaker from just about everywhere and for just a few dollars I could have a turn key engine.  Keeping in mind also that at first I thought it was a 350 so  I'm still on the fence.  My time is free, I work at the base auto club so I don't have to pay for any of my work hours.  Still wondering about the HP difference between gross and net though, I wish I knew what both engines are gross and net to see if I would in fact be taking a HP hit...

[muddpuppy01]

gross is brake hp and net is to the wheels

I would guess look at the cameros for that info

[Captkaos]

Any motor from 1969 isn't going to be running at peak horsepower, so if you are thinking you are going to gain power by putting in an old worn out motor you may want to lower your expectations, A LOT.

ALL Small blocks will interchange parts, the only caveat is the older heads with no accessory hole, and hopefully non one is using those old dinosaurs now.  Pre 1968 cranks were small journals which is the other difference.  Everything else it the same. (until you get to 1987 with the manifold bolts changing, still nothing a head change won't fix) 

A 307 is a block with a 283 bore (3.875") and a large journal 327 crank.  The crank will go any any post 1968 large journal block (any.... 305, 327, 350, 400) Rods are the same as any SBC, the mains will be 2 bolt, the heads are the same as any SBC out there with the same bolt pattern.  If you want to wake it up, put some Vortec heads on it.

There is nothing special about a 307 that you can't find parts for them.  If you are wanting 307 heads specifically sure, by that would be trying to find a 2 bbl manifold for a performance  SBC.  With that said there is nothing specail about a 350 for that matter.  If you pulled one and the casting number says it came out of a Corvette, who cares, it is still JUST and SBC, you aren't gaining anything by the block being out of a Corvette...  You could do the same exact power levels with one from a pickup truck.