bwiencek

I've been doing a lot of reading and searching here on repowering, cam choices, 355 vs. 383's, auto engines vs 'marine' engines, etc., so I've got myself thouroughly confused

My question is this - I've got a 383 rotating assembly that I bought for another project but decided on a 406 for that one instead. I'm thinking about putting it together for the boat instead and was wondering if there are any major concerns with the combo or anything that stands out as something to change in the combo before even wanting to run it in a marine application

Block is a 2pc seal, 2-bolt main 010 block, it's been bored/honed .030 over and honed with torque plates. Block was clearance checked for the setup, tanked, line honed, new bearings/freeze plugs, deck was checked but not cut
Rotating assembly consists of a summit racing 383 "kit" - cast crank, 4340 I-beam rods, KB135 pistons, clevite bearings. Assembly was balanced to a stock 400 balancer and flexplate

Heads are 64cc world products sportsman II assemblies that come with springs for a flat tappet cam good for .560 lift. and Manley Street Flo valves. Compression is 9.7:1 advertised, but with the headgasket at .041 and a below deck .010 it brings it down to around 9.5:1

Camshaft choice is up in the air right now - I've got an XM262H in the 350 right now and think it runs out of breath on the top end so I'm wanting something that runs more RPM's there. and I'll re-use the holley street dominator high-rise dual plane intake and edelbrock 750 carb that's on the 350 right now.

Exhaust is all stock right now - although I'm leaning towards a set of GLM aluminum manifolds with their aluminum risers running thru-prop on an alpha one outdrive (I know no big holeshots with the 383... I'm willing to take a chance on it ) Only boating is in freshwater and it's raw-water cooled.

Here's the questions -

Right now the Piston-to-wall clearances were set for street/strip use at .002-.0025" - which I'm thinking I need to open them up a bit. - how far to tell the machine shop to go?? .0030 enough?

What would be a good cam to run with this combo?

Are the GLM aluminum manifolds worth the cost (HP wise?)

Do I need to change out the exhaust valves to their severe duty valves or just widen the seat contact to something around .100" (world says they grind them around .060 wide)

Where can I get a 400 (ext. balance) flywheel for the marine application or can I run a 'regular' car/truck flywheel?

Any glaring holes in this combo??

Any help from the pro's here is greatly appreciated....

excalibur32

set up the mains and rods to.003 the exhaust valve guides need to be opened up since they run cooler than a car, have them put 4 bolt main caps on, should use a steel crank. Cam Teqniques has the cam you need. the exhaust is worth it I like the eddie marine thunder.

excalibur32

Oh the alt, starter, and carb and distributer must be coast guard approved.

bwiencek

I'll check the rods/main clearance - can't remember what they're at. I'm not a fan of 4-bolt caps unless doing a splayed main cap but at the RPM's that I'm talking about turning I've never had a stock main cap fail. I've spun my circle track engine with stock 2-bolt mains up to 65-6700 for 3 seasons without a failure.


Only thing left I can think of is the flywheel - can I use a replacement flywheel from a pickup with a 400 and manual tranny - or is there a marine specific 400 flywheel??

David Stotz

You did not mention if you had a budget but here goes. I would change the pistons to forged if they are not. If you have the stock exhaust reuse it. The GLM is not much different, just a littlt lighter. If you have to buy new exhaust go to something with internal runners like Stainless Marine or similar. Be careful of the cam you use with the thru prop exhaust, do not get too long on duration. I like hydraulic roller cams. The two bolt block will be fine.

excalibur32

Boat engines are under constant load steel crank and 4 bolt mains really are a necessity. Pin them too. Merc has a 383 now have somebody look up the cam choice for you. They also made a 377 smallblock. contact mrhorsepower on here he builds good engines as does Tyler Crockett and they are pretty visiable.

bwiencek

Of course there's a budget - it's whatever the "boss" says I can spend If I don't buy the lighter exhaust setup that will free up some cash. I'd do the roller cam if it was a late model block that was already set up for it. I've got a line on a good '98 vortec pickup engine that is supposed to be a 4-bolt main and I can pick up and it's already fitted for stock hydraulic roller stuff - I'd just have to get it built with other internal components...

If I've got to go steel crank and forged pistons I might as well build something else... When yoy say "Pin them too" - are you referring to rocker studs?? (the heads already have screw in studs with guideplates)

I guess I should say that I'm not looking for huge HP - 325hp would probably be fine which is 25% more or so above the stock mercruiser engine - something a little stronger than a stock but don't want to put a $10k engine into it.

How much are those 377/383's? Can they be had in a long-block form?

excalibur32

If you put 4 bolt main caps on you can dowl pin them too, like on the outside of the cap to the block just machine straight down and then pin it stops forward and back movemnet of the caps, or you can use the splayed caps but pinning is cheaper. Merc rebuild I think sells the 383, the stinger 377 was new and no longer in production, but the are some around with warranties, google them.

1BIGJIM

You say that I'm not looking for huge HP - 325hp
You will be perfectly fine with a cast crank, and two bolt mains, and Hyper Pistions. I think I read you are using KB pistons. Make sure you follow the end gap instructions. The top ring gap is huge, If I remember its around .022. I have used them on mild builds several times. My spare 454 has KB pistons. You might want to reconsider using a roller cam. Keep the stock exhaust and put the money to something else.
Good luck it sounds like you are on the correct path.

Ryan00TJ

I've ran those same piston clearances before on previous marine SBC's with no problems. I put 365 hours on a 360ci SBC with a cast crank, rods and cast pistons 2 bolt 010 block also. Revved to 5500-5700rpms with no problems. Upon teardown everything looked fine. I have it in the garage as a spare shortblock in case I ever need one.

I've ran a 224/224 .465/.465 114+5 flat tappet before with stock manifolds and no reversion but with thru hull. Going thru the Y pipe could be different. As to any cam you choose make sure to pull the manifolds and check for signs of reversion. You'll be fine with your setup and meet your power goals pretty easily even with the stock exhaust. Just watch for reversion and read the plugs to prevent detonating the hyper pistons as they are very brittle and do not tolerate detonation well.

I know a few guys on here liked the XM270 226/236 in their 383's but they were running thru hull and better manifolds.